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• Capture zone distributions (CZD) were plotted for 2D Ge islands nucleated on Si(111)-(7 × 7) terraces at 550–650 °C. • Obtained CZDs were described by generalized Wigner distribution. • Critical nucleus size of 2D Ge island was found to consist of 3–5 particles. • CZD analyses indicates on AL kinetics of 2D Ge nucleation at elevated. T Recently we have studied the concentration N 2 D of 2D Ge island nucleated on large-scale Si(111)-(7 × 7) terraces at 550 − 650 °C as function of the substrate temperature T and Ge deposition rate R [J. Cryst. Growth. 531 (2020) 125347], where we have shown that N 2 D (R) dependence is characterized by a power law with scaling exponent χ = 1 ± 0.1. However, in the frames of classical Venables rate-equation approach, the obtained range of χ values do not allow one to unambiguously determine the critical nucleus size i , since χ = 1 ± 0.1 can be attributed to both diffusion limited (DL) and attachment limited (AL) growth regimes. In order to determine an exact i size and growth kinetics, in this work, we have investigated the scaled capture-zone distribution (CZD) of nucleated 2D Ge islands on the same Ge/Si(111)-(7 × 7) samples and described it by the generalized Wigner distribution P β = a β A β exp - b β A 2 , where P β is the probability density of getting into some region of capture zone values, A is normalized Voronoi cell area for 2D island, β = i χ is scaling parameter directly related to the critical nucleus size i. It has been shown that the kinetics of 2D Ge island nucleation on the wide Si(111)-(7 × 7) terraces at elevated temperatures should procced under AL growth kinetics with i = 3–5 particles. [ABSTRACT FROM AUTHOR]

• Al 0.9 Ga 0.1 N alloys grown by PA-MBE show clear evidence of phase segregation in XRD. • XRD peak shows splitting: Peak separation changes with varying growth parameters. • Weighted averages of XRD peaks remain the same: Overall composition is unchanged. • Long-range atomic ordering is observed in alloys with minimal phase segregation. • Route to efficient deep-UV emitters through carrier localization at bandgap minima. AlGaN alloys with very high AlN mole fraction (∼90 %) were grown by plasma-assisted molecular beam epitaxy (PA-MBE) and their alloy properties were investigated by high-resolution X-ray diffraction (HR-XRD) measurements. Growth was carried out employing a series of group III/V ratios and for samples grown under a high group-III regime, phase-segregation in the alloy was evident from a characteristic splitting of the AlGaN (0002) peak in the HR-XRD pattern. With decreasing excess group-III conditions the separation of peak positions continuously reduced, till a single peak was observed. However, for samples where such splitting was absent, spontaneous superlattice peaks were seen at lower incident angles of the XRD patterns indicating the presence of long-range atomic ordering (LRAO). Thus, for AlGaN alloys with extremely high Al content, effects of phase-segregation, or of LRAO were observed, depending on the kinetics of growth. These results on phase-segregation effects are expected to promote the development of high-efficiency deep ultraviolet emitters for skin-safe germicidal action by mitigating the detrimental effect of dislocations and related non-radiative recombination centers through carrier localization processes at potential minima. [ABSTRACT FROM AUTHOR]

• Amorphous SnSe 2 layer was crystallized by heating to 250 °C to initiate vdW epitaxy. • SnSe 2 film screw dislocations density is ∼18 and ∼2 μm−2 for Si and Bi 2 Se 3 substrates. • SnSe 2 film has a hexagonal lattice structure (space group P 3 ¯ m 1 (no. 164)) • Decrease in Se:Sn flux ratio switches SnSe 2 epitaxy to nucleation of SnSe 3D islands. We have studied the structural and morphological features of SnSe 2 films grown on Si(111) and Bi 2 Se 3 (0001) surfaces in an in situ reflection electron microscope. On both substrates, the SnSe 2 growth started at 100 °C as an amorphous layer, and when thickness reached 1 nm, crystallized by raising the growth temperature to 250 °C without interruption of Sn and Se fluxes. The introduction of this growth-initiating stage has decreased the concentration of screw dislocations on films' surfaces to ∼18 and ∼2 μm−2 for the Si(111) and Bi 2 Se 3 (0001) substrates, respectively. High-resolution transmission electron microscopy investigation has shown that the layered SnSe 2 film has a hexagonal lattice structure corresponding to the space group P 3 ¯ m 1 (no. 164) with lattice parameters a = 0.38 nm and c = 0.62 nm. Raman spectroscopy has shown vibrational modes corresponding to the 1T-SnSe 2 phase. We have shown that the decrease in Se:Sn flux ratio switches growth mode from Frank—van der Merwe type SnSe 2 epitaxy to Volmer—Weber type nucleation of SnSe 3D islands. [ABSTRACT FROM AUTHOR]

• Impurity-induced 2D phase forms on Bi 2 Se 3 surface during submonolayer In deposition. • Islands of indium-induced surface phase have a height of 0.4 nm. • During indium deposition, area of the surface phase increases until complete coverage. • The phase locally suppresses sublimation, which creates multilayer star-shaped islands. Using in situ reflection electron microscopy, transformations of Bi 2 Se 3 (0001) surface during In deposition have been studied. We first report the formation of an In-induced surface phase that precedes nucleation and growth of a layered In 2 Se 3 at substrate temperatures around 400 °C. The surface phase nucleates on Bi 2 Se 3 (0001) terraces as islands having high In content and a height of 0.4 nm. During continuous In deposition, the area of these islands increases and suppresses Bi 2 Se 3 sublimation from the regions covered by the In-induced surface phase. This locally suppressed sublimation and sublimation-induced ascending motion of Bi 2 Se 3 atomic steps create multilayer triangular star-shaped islands. [ABSTRACT FROM AUTHOR]

Abstract In this report, ferromagnetic interactions in modulation-doped GaMnN nanorods grown on Si (111) substrate by plasma-assisted molecular beam epitaxy are investigated with the prospect of achieving a room temperature ferromagnetic semiconductor. Our results indicate the thickness of GaN layer in each GaN/MnN pair, as well as Mn-doping levels, are essential for suppressing secondary phases as well as enhancing the magnetic moment. For these optimized samples, structural analysis by high-resolution X-ray diffractometry and Raman spectroscopy verifies single-crystalline modulation-doped GaMnN nanorods with Ga sites substituted by Mn atoms. Energy dispersive X-ray spectrometry shows that the average Mn concentration can be raised from 0.4 to 1.8% by increasing Mn fluxes without formation of secondary phases resulted in a notable enhancement of the saturation magnetization as well as coercive force in these nanorods.

• MBE growth of Cd 1−x Mn x Te films on Si (1 1 1) substrate. • AFM for the surface morphology and roughness. • XRD and PL spectra to estimate the Mn concentrations. • Room temperature Raman spectra to obtain the vibrational modes. Semiconductors structures with high quality and low cost have been developed and applied in industry on a large scale. The knowledge of basic properties of semiconductor materials growth is important for many technological applications. Cd 1-x Mn x Te films have been used successfully in optoelectronic, solar cells and high energy detectors applications. However, despite the high potential for application of these films, fundamental growth studies on Si(1 1 1) substrate are not extensively explored. In this study, two Cd 1−x Mn x Te (CMT) films (with different Mn concentrations) were successfully prepared on Si(1 1 1) substrate employing molecular beam epitaxy. The morphology and surface roughness of the films were investigated using atomic force microscopy (AFM). X-ray diffraction was used to investigate the structural quality and to determine the Mn concentration of the samples. It shows that the films have only (1 1 1) orientation despite a lattice mismatch of almost 19%. Room temperature micro-photoluminescence (µ-PL) spectra shows a high intensity band edge emission and very low intensity defect related emission. Raman spectroscopy of the samples was carried out in order to obtain the vibrational modes. First, second and third order CdTe-like and MnTe-like longitudinal-optical (LO) phonon modes were observed. These results demonstrate the potential of these structures for room temperature applications. [ABSTRACT FROM AUTHOR]

• Capability to monitor growth rate of III-Nitrides, by MBE, at any point during the growth of the film or device structure. • Innovative differential analysis method which increases accuracy (reduces error) by more than 2x over previous methods. • Measurement of the Ga adlayer thickness made by RHEED Intensity analysis for the first time. The standard method for growth rate determination in semiconductor thin films, by Molecular Beam Epitaxy (MBE), is through RHEED intensity oscillations prior to device layer epitaxy. High quality III-Nitride epitaxy occurs with metal-rich surfaces and under step-flow growth conditions, which do not produce RHEED oscillations. This article demonstrates the capability to monitor the growth rate of gallium nitride (GaN), at any point during film growth with high fidelity, under step-flow growth conditions. RHEED intensity vs. time measurements determine the growth rate by Metal Modulated Epitaxy (MME). Utilizing differential analysis, a factor of 2x improvement in accuracy is demonstrated, with a Standard Error less than 4%. Complementary analysis with X-Ray Diffraction and RHEED identify the Ga bilayer thickness as 2.34 ML ± 0.08 ML, representing the first time RHEED analysis has been used to characterize the thickness of the Ga bilayer on GaN. [ABSTRACT FROM AUTHOR]

Highlights • Epitaxy of high Bi content GaSbBi alloys investigated by combinatorial MBE. • Epitaxial phases with distinct structural and Bi incorporation characteristics established. • Phases are mapped by Sb/Ga ratio and growth temperature over broad parameter space. • Phase with optimal structural quality is suppressed by increase of Bi/Ga ratio. Abstract GaSbBi alloys have recently emerged as attractive materials for mid-infrared optoelectronics owing to strong band gap reduction enabled by Bi incorporation into the GaSb matrix. The fundamental understanding of the epitaxial process required to demonstrate high quality crystals is in an early-developmental phase. From this perspective, we report on the key role played by the Sb/Ga flux ratio in controlling the structural quality and incorporation of high Bi content GaSbBi (up to 14.5%-Bi), revealing three distinct epitaxial phases. The first phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low crystal quality, and reduced Bi content. At the second phase (above stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent crystallinity with efficient Bi incorporation. The last phase corresponds to exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets and degraded crystallinity. This threshold value that defines the optimal growth window is controlled by the temperature as well as the Bi/Ga ratio. Increasing temperature increases the threshold, albeit simultaneously reducing Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi incorporation, while narrowing down and ultimately closing the window. This study provides a general framework enabling development of high quality GaSbBi heterostructures for emerging mid-infrared optoelectronics. [ABSTRACT FROM AUTHOR]

Highlights • PL emission properties of RTA treated TI samples are a combination of the QW and QDs behavior. • Samples treated with higher RTA temperatures show improved emission properties. • Static parameters of QD lasers drastically improve with higher RTA temperature. • Prediction of TI QD lasers performance change after RTA temperature difficult, due to competing processes. • Material quality improvement and band alignment changes have to be considered for appropriate RTA treatment of TI QD lasers. Abstract An InP based tunnel injection quantum dot (QD) laser and a reference quantum dot laser designed to emit at 1.55 μ m were grown by molecular beam epitaxy. The lattice matched tunnel injection (TI) structures consist of an InGaAs quantum well (QW), an InAlGaAs barrier and multiple InAs quantum dot layers. Quantum well and quantum dot test structures as well as the actual laser structures were treated with rapid thermal annealing (RTA) at varying temperatures (680–780 °C). Photoluminescence measurements were performed at 10 K on all samples and a strong effect of this annealing process on the emission properties is observed. The laser structures were processed into broad area lasers. Power-current characteristics were measured and evaluated. A strong improvement in device performance is observed after annealing for QD lasers while for TI-QD lasers no significant improvement was obtained, which might be caused by detuning of band energy alignment and different impact of the RTA process on the material quality of QW and QD layers. [ABSTRACT FROM AUTHOR]

Highlights • A fast algorithm for the study of reflectance anisotropy (RA) spectra is developed. • Detection of two fundamental components of RA spectra during GaAs homoepitaxy. • Application of RA spectroscopy to surface stoichiometry prior to homoepitaxy of GaAs. Abstract We report on a computer algorithm for the in situ analysis of reflectance anisotropy (RA) spectra in a time frame compatible with the epitaxial growth of cubic semiconductors. This algorithm allows for the in situ acquisition of RA spectra and their decomposition into two components whose amplitude depends on the As coverage of the semiconductor surface. One of such components is associated with the surface orthorhombic strain due to the surface reconstruction and has an amplitude that strongly depends with surface reconstruction and thus As coverage. This fact opens the possibility of using reflectance anisotropy spectroscopy (RAS) as an optical probe to characterize the As surface coverage in real time. To demonstrate the performance of the algorithm we report on RA measurements carried out during the homoepitaxial growth of GaAs (0 0 1). We show that the algorithm is capable of analyzing a set of 500 RA spectra in a time span of about 10 s. This allows for a range of applications for the developed algorithm, including the surface characterization and fine tuning of the substrate stoichiometry just before epitaxial growth, during the growth of the buffer layer. [ABSTRACT FROM AUTHOR]

Highlights • The multi-junction solar cells were grown by MBE. • A higher growth temperature is good for GaInP and InGaAsP. • Multi-junction solar cells were fabricated by wafer bonding technique. • The optimiztion process of four-junction solar cell was discussed. Abstract We report on the room-temperature wafer-bonded InGaP/GaAs//InGaAsP/InGaAs four-junction solar cell grown by all solid-source molecular beam epitaxy (MBE). The material growth and structure optimization of multi-junction solar cell were investigated. The effect of growth temperature on phosphide-related material of the solar cell was discussed. The lattice-matched InGaP/GaAs tandem cell on GaAs substrate and InGaAsP- or InGaAsP/InGaAs-tandem cell on InP substrate were grown separately by MBE. Room-temperature wafer bonding technique was used to integrate the subcells into multi-junction solar cells. The current limiting of multi-junction cells was analysed and the device structure of four-junction solar cell was optimized. The best wafer-bonded four-junction solar cell reached a conversion efficiency of 42% under concentration. [ABSTRACT FROM AUTHOR]

Highlights • Ga nanodroplets on SiO 2 /Si substrate are studied by XPS. • Ga oxides are formed due to the Ga/SiO 2 interaction. • Ga nanoparticles induce the formation of nanoholes in the SiO 2 layer. • GaAs nanowires are grown from these nanoholes and studied by XPS. Abstract In this paper the early stages of the self-catalyzed Vapor-Liquid-Solid (VLS) growth of GaAs nanowires on Si substrates by Molecular Beam Epitaxy (MBE) are studied. The interaction of Ga nanodroplets (NDs) with the silica overlayer is investigated by X-ray Photoemission Spectroscopy (XPS) and Atomic Force Microscopy (AFM). We show how Ga NDs drill the silica overlayer and make contact with bulk Si to allow GaAs nanowires (NWs) epitaxial growth by studying each of the three steps of the NW growth process sequentially: Ga NDs pre-deposition, post-deposition annealing to reach the NW growth temperature, and finally NW growth itself. The pre-deposition temperature allows to control the density and morphology of the NDs. A high enough annealing temperature enhances the reduction of SiOx by Ga oxidation and leads to the formation of holes which is seen by a new component in XPS spectra, assumed to be the consequence of the Ga Si interaction. Finally, these nano-holes act as nucleation sites for the epitaxial GaAs VLS growth. During the GaAs growth, three different chemical environments of Ga are identified in Ga2p core level: metallic Ga due to the droplets at the top of the NWs, Ga oxide in contact with the SiOx overlayer and Ga arsenide from NWs. [ABSTRACT FROM AUTHOR]

Highlights • Slight variations in ultrathin AlN prelayers result in drastic GaN NW changes. • Increasing the AlN nominal thickness between 0 and 0.5 nm, doubles NW heights. • Simultaneous increase in NW height and decrease in diameter and density is found. Abstract The effects of ultrathin AlN prelayers, with nominal thicknesses between 0 and 1.5 nm, on the spontaneous growth of GaN nanowires (NWs) on Si (1 1 1) substrates were investigated. The morphological and structural characteristics of GaN NWs were analyzed by electron microscopy and X-ray diffraction techniques. The results quantify how the AlN prelayer thickness affects GaN NWs. The increase of AlN thickness gradually limits nitridation of the substrate surface and accelerates 3D GaN nucleation. The formation of amorphous Si x N y by Si nitridation is completely avoided for 1.5 nm of AlN that fully covers the Si surface. The dependence of the height, diameter and density of GaN NWs on the AlN thickness was also determined. The 1.5 nm AlN provided the optimum condition for GaN NW nucleation and growth; the NWs exhibited a large homogeneous height with almost no parasitic GaN formation between them. High resolution transmission electron microscopy showed the full relaxation of misfit strain of AlN on Si (1 1 1) and of GaN NWs on AlN. In-situ reflection high energy electron diffraction during AlN nucleation revealed the immediate relaxation of the AlN prelayer before GaN NW nucleation. Formation of β-Si 3 N 4 before AlN nucleation was also observed. [ABSTRACT FROM AUTHOR]

Highlights • Nanocolumn selective-area growth was achieved by nanosphere lithography and etching. • The shadow effect and Ti growth suppression contribute to selective-area growth. • InGaN sections selective-area grown could be beneficial to uniform In distribution. Abstract In this paper, the selective-area growth (SAG) of GaN-based nanocolumns (NCs) on silicon (Si) has been investigated experimentally. A low-cost and facile method has been proposed and implemented to fabricate the SAG NCs, which contains the processes of nanosphere lithography (NSL) and plasma-assisted molecular beam epitaxy (MBE). SAG NCs grown by this method indicates a higher ability to modulate the NC distributions than those grown by the conventional patterned method. According to photoluminescence results, InGaN/GaN NCs grown on Si nanopillars produced by NSL and etching show the more uniform indium (In) distribution than those grown on the openings of patterned Si substrate. Furthermore, according to the kinetic processes during MBE growth, it is proposed that the SAG of NCs results from the combination of the shadow effect of Si nano-pillars and the growth suppression of titanium (Ti) film. [ABSTRACT FROM AUTHOR]

Highlights • Modelled the thermal dynamics of an Al effusion cell as a linear system. • Grew smooth parabolic quantum wells in AlGaAs with molecular beam epitaxy. • Obtained excellent control over Al composition at typical growth rates. • Developed a general method which could be extended to other structures or materials. Abstract Parabolic quantum wells have unique properties that make them attractive for certain applications. However, growing them with molecular beam epitaxy is much more difficult than growing standard rectangular wells, as parabolic wells require a smooth, precise variation of the composition during growth. Typically, such composition variations have been approximated using the digital alloy technique, but there are limits on the quality of wells that can be produced this way. In our approach, we instead create a smooth parabolic potential in Al x Ga 1 - x As by varying the Al cell flux as a function of time. To compensate for thermal lag in the effusion cell, we develop a simple linear dynamical model, which can be inverted to find the temperature input required for a desired composition profile. With this approach, the composition in a 3 THz Al x Ga 1 - x As parabolic quantum well can be controlled to a root-mean-squared error of 0.4% Al. This approach can be easily generalized to other structures, and, importantly, can be used at typical growth rates (1.5 - 2.5 Å / s), which allows for the growth of parabolic well arrays. [ABSTRACT FROM AUTHOR]

Highlights • Si doped GaAsN has smaller electron concentration than Si doped GaAs. • Large electron activation energy is observed to be 71 meV. • Localized band in GaAsN is the cause of large electron activation energy. • Localized band in GaAsN has small density of states. • The main factor of decreased Si activation ratio depends on both [Si] and [N]. Abstract The Si doping mechanism is systematically investigated in dilute nitride GaAsN grown by radio frequency plasma assisted molecular beam epitaxy (RF-MBE). We change growth temperature, Si impurity concentration ([Si]), and nitrogen composition ([N]). The relationship between Si activation ratio (α) and [N] are evaluated using X-ray diffraction (XRD) 2θ-ω and Hall effect measurement. As [N] in GaAsN increases, α drastically decreases, which is ascribed to mechanisms of inactive Si donors such as a cluster of Si and N at an As site ((Si-N) As). We find that the main factor of inactive Si donors in GaAsN depends on both [Si] and [N]. [ABSTRACT FROM AUTHOR]

Highlights • Thin Ge buffer layers on Si as an alternative to thick GaAs buffers on Si. • TDD density in 270-nm-thick Ge buffer layers comparable to 1300-nm-thick GaAs buffers. • Overall thickness reduced by at least 1 μm without impact on crystal quality. • Lower thickness prevents cracking and reduces cost of III-V integration on silicon. Abstract Development of Si-based lasers is considered as the key to the realisation of fully integrated Si photonic circuits. Monolithic growth of III-V lasers on Si substrates is one of the most promising solutions for developing a commercially viable Si-based laser. However, the performances of current devices are still hindered by defects, hence the optimisation of crystal quality of the laser structures is of paramount importance. This paper reports on growth optimisation of thin Ge buffer layers on Si as an alternative to thick GaAs buffer layers. This method reduces the overall thickness and lowers the threading dislocation density in III-V semiconductors integrated on silicon platform. [ABSTRACT FROM AUTHOR]

Highlights • Design and growth of broadly tunable hetero-cascading quantum cascade lasers. • Influence of electric field and interface roughness on the gain spectra. • Interface roughness is shown to play an important role for broadband lasers. • External cavity configuration has been used to extract narrow-band emission. • Single-chip tuning range of 400 cm−1 by using tri-stack active regions. Abstract Design and growth characteristics of broadly tunable hetero-cascading quantum cascade lasers are discussed. We show the influence of electric field variation, and interface roughness on the gain spectra. Interface roughness is shown to play an important role for these broadband lasers. External cavity configuration has been used to extract narrow-band emission, thus rendering wide tuning range of the device. We achieve a single-chip tuning range of 400 cm−1 (from 1030 cm−1 to 1430 cm−1, namely 7.0–9.7 µm in wavelength) by using tri-stack active regions. [ABSTRACT FROM AUTHOR]

Highlights • The InGaAs DWell solar cell of 15-nm spacer has the best photovoltaic performances. • A study of DWell and QDs solar cells has been reported. • The photovoltaic response of the DWell solar cell is improved by Al 2 O 3 /HfO 2 AR coating. Abstract To improve the performance of self-assembled InGaAs quantum dots (QDs) solar cells, we introduce a 2-nm In 0.1 Ga 0.9 As quantum well underneath each In 0.75 Ga 0.25 As QDs layer to form an InGaAs quantum dots-in-a-well (DWell) structure. The coupled DWell solar cell consists of nine DWells spacing by GaAs layers. We change the GaAs spacer thickness to optimize the photovoltaic performance. The solar cell of 15-nm GaAs spacer shows the best results, including the open-circuit voltage (V OC) = 0.67 V, the short-circuit current density (J SC) = 17.4 mA/cm2, and the power conversion efficiency (η) = 8.7%, compared to the coupled InGaAs QDs counterpart of V OC = 0.59 V, J SC = 18.6 mA/cm2, and (η) = 8.0%. The enhancement of V OC for the DWell solar cell is attributed to the lower dark saturation current, which is caused by stronger carrier confinement and lower strain-induced defects in the active region. The DWell solar cell is further improved by Al 2 O 3 /HfO 2 anti-reflection coating, and reaches η = 11.8% as J SC increases to 23.5 mA/cm2. [ABSTRACT FROM AUTHOR]

Highlights • High quality ZnTe layers were prepared on the sapphire substrates. • S-, c-, a-, and r- sapphire showed step terrace structure after the annealing. • Nanofacet structure was observed from the m- sapphire surface after the annealing. • Those structures were very effective to improve the crystal quality of ZnTe layers. • ZnTe layers on sapphire were doped using nitrogen. High p-type doping was confirmed. Abstract ZnTe layers were grown on various orientation surfaces of sapphire substrates, namely c-, a-, r-, and S-planes. Single domain dominant layers were achieved by carefully controlling the substrate orientation and introducing the thin buffer layer. The substrate surfaces were annealed at approximately 1000 °C to achieve an atomically smooth surface with step-terrace structures. Single domain layers were achieved by employing the step-terrace structured substrates. A nanofacet structure of the substrate surface consisting of the r-plane and the S-plane was obtained by annealing the m-plane substrate surface. Nucleation of ZnTe occurred along the nanofacet. It was confirmed that preferential nucleation of ZnTe on the S-plane of the nanofacet took place. Nitrogen doping of the ZnTe layer was performed, with the doping efficiency confirmed as being as good as ZnTe layers prepared on GaAs substrates. This is another indication of the high crystal quality for the prepared ZnTe layer. [ABSTRACT FROM AUTHOR]

Highlights • Successful growth of crystalline CFS/MgO/GaAs heterostructures by MBE. • MgO interlayers act as diffusion barriers in CFS/MgO/GaAs hybrid systems. • MgO interlayers suppress the diffusion of Co and Fe atoms into the GaAs layer. • MgO interlayers suppress magnetic interaction of the CFS/GaAs interface. • In-plane rotation of the easy axis by 90 degree for samples with MgO interlayer. Abstract We demonstrate the growth of crystalline Co 2 FeSi/MgO/GaAs(0 0 1) hybrid structures of different MgO interlayer thicknessess by molecular beam epitaxy. The MgO layer thickness was verified by X-ray reflectivity measurements and high-resolution transmission electron microscopy images. Secondary ion mass spectroscopy confirmed that the MgO layer works successfully as a diffusion barrier. Co and Fe defect densities in the GaAs layer could be reduced by three orders of magnitude using a 1.3 nm thick MgO film. High-resolution transmission electron microscopy images together with X-ray diffraction phi scans also revealed an in-plane rotation of the Co 2 FeSi layer by 45 ° for samples with MgO interlayers with respect to the GaAs substrate. Investigations of the magnetic properties revealed that the MgO interlayers do not affect the value of the magnetic moment of the Co 2 FeSi layer. Further, an in-plane rotation of the easy axis of the Co 2 FeSi layer by 90 ° for all samples with MgO interlayers was observed and will be discussed. [ABSTRACT FROM AUTHOR]

Highlights • Deep-UV emission at 260 nm has been obtained from AlGaN-based MQW structures. • High AlGaN and AlGaN/AlN MQW structures has been grown by PA-MBE. • Larger Al flux ratio and higher growth temperature contribute to increasing Al content of AlGaN. • The emission wavelength was tuned by controlling the thickness of AlGaN quantum well. Abstract Deep ultraviolet (UV) emission at 260 nm has been obtained from high Al content AlGaN/AlN multi-quantum well (MQW) structures by plasma-assisted molecular beam epitaxy (PA-MBE) on AlN template on sapphire substrates. The effect of III/V ratio and growth temperature on structural and optical properties of AlGaN was studied. It was observed that Al content in AlGaN material increased with increasing Al flux ratio or growth temperature. By altering growth conditions, AlGaN with high Al content of 47–80% was obtained. Further studies indicate that AlGaN layers have excellent surface morphology and optical properties grown in slightly metal-rich condition. As for AlGaN/AlN MQW, the emission wavelength was tuned by controlling the thickness of AlGaN quantum well, and deep ultraviolet emission below up to 260 nm was obtained from AlGaN (2.4 nm)/AlN(6.9 nm) MQW at room temperature. [ABSTRACT FROM AUTHOR]

Highlights • Interdigitated type-I and type-II quantum dots are grown by molecular beam epitaxy. • Type-I InAs/GaAs and type-II GaSb/GaAs quantum dots are utilized. • The interdigitated quantum dots are incorporated into a heterojunction solar cell. • By comparing with the homojunction cell, V OC is improved by 20.6%. Abstract Interdigitated quantum dots, which are multiple stacks of type-I InAs/GaAs quantum dots and type-II GaSb/GaAs quantum dots, are grown using molecular beam epitaxy. By incorporating the interdigitated quantum dots into a p - i - n AlGaAs/GaAs heterojunction solar cell structure, we demonstrate a photovoltaic effect with a 20.6% improvement in open-circuit voltage, when compared to that of another cell incorporating the same quantum dots but with a p - i - n GaAs homojunction architecture. A transmission electron microscopy is performed to analyze strain-induced defects created in the multi-stack quantum dot structures. The heterojunction solar cell incorporating the interdigitated quantum dots realized in this work would find potential applications in high-efficiency single-junction intermediate band solar cells operating under concentrated sunlight. [ABSTRACT FROM AUTHOR]

Highlight • The planar Hall resistance measurements revealed two GaMnAs layers have opposite sign of AMR. • Alignment of magnetizations between GaMnAs have been identified form Hall measurements. • GaMnAs trilayer showed GMR-like effect that arises from the noncollinear configurations. Abstract The magnetotransport properties of a GaMnAs trilayer in which two GaMnAs layers are separated by a nonmagnetic GaAs:Be spacer has been investigated during the magnetization reversal process. Interestingly, the planar Hall resistance (PHR) reveals that the two GaMnAs layers in a trilayer structure have opposite signs of anisotropic magnetoresistance (AMR). The magnetoresistance is observed to be significantly different for the collinear and noncollinear magnetic alignment, which indicates that the presence of the giant magnetoresistance (GMR)-like effect in the system. This GMR-like effect was systematically investigated during the process of magnetization reversal using field and angle scans of MR measurements. [ABSTRACT FROM AUTHOR]

Highlights • In-LDE is suited for etching of very deep nanoholes. • High thermal stability of In-etched nanoholes. • Intermixing between etching and substrate material. • Integration of In-LDE inside AlGaAs material-system possible. Abstract In contrast to Indium droplets the usage of Ga or Al droplets for the local droplet etching (LDE) technique is well established. It has been shown previously that In-droplets or In-alloys can be used for LDE with focus on small hole-depths at low etching temperatures. With our recent experiments we reveal that In-LDE is also well suited for the creation of very deep nanoholes (exceeding 100 nm) and very low densities in the range of 106 cm−2 for large average distances of several micrometers. The unexpected high thermal stability of the etching process itself as well as the formed wall-like structures clearly points to an intermixing between etching and substrate material during the LDE-process. This can be related to the lack of As during LDE. Additional experiments with capping layers also reveal high surface-roughness probably caused by a lattice mismatch, which can be also explained by intermixing. A second LDE step with Al can be applied to avoid roughening effects. [ABSTRACT FROM AUTHOR]

Highlights • Cu 2 O epilayers with orientations from 〈1 1 0〉 to 〈1 1 1〉//ND were grown successfully by PA-MBE on Cu. • The Cu 2 O epilayer and Cu substrate follow a cube-on-cube orientation relationship. • The epitaxial growth of Cu 2 O is more sensitive to the oxygen pressure than plasma power. • The roughness of the substrate surface plays no effect on the epitaxial growth. Abstract Cuprous oxide (Cu 2 O) films were grown on polycrystalline and singlecrystalline copper substrates by plasma-assisted molecular beam epitaxy (PA-MBE) to evaluate the effects of substrate temperature, grain orientation, oxygen pressure and plasma power on the epitaxial growth of Cu 2 O. The copper substrate was annealed and electro-polished prior to the epitaxial growth. Following the MBE growth, the deposited films were analyzed by X-ray diffraction and electron backscatter diffraction equipped in a scanning electron microscope. The results indicate that Cu 2 O grows epitaxially on substrate grains with orientations distributed from 〈1 1 0〉//ND to 〈1 1 1〉//ND (here ND represent the normal direction of the sample) within a processing window of proper oxygen pressure and plasma power at 650 °C substrate temperature. [ABSTRACT FROM AUTHOR]

Highlights • Sublattice reversal from (1 1 3)B to (1 1 3)A was realized in GaAs/Ge/GaAs. • Sublattice reversal from (1 1 3)A to (1 1 3)B was realized in AlAs/Ge/AlAs. • Self-annihilation of antiphase domains was responsible for sublattice reversal. Abstract GaAs/Ge/GaAs and AlAs/Ge/AlAs heterostructures were grown both on (1 1 3)B and (1 1 3)A GaAs substrates by molecular beam epitaxy. Sublattice reversal in these heterostructures were identified by comparing the anisotropic etching profile of the epitaxy sample with that for reference (1 1 3)B and (1 1 3)A GaAs substrates. Sublattice reversal in GaAs/Ge/GaAs heterostructures was achieved on (1 1 3)B GaAs substrate. On the other hand, sublattice reversal on (1 1 3)A GaAs substrate was obtained by using AlAs/Ge/AlAs heterostructures. [ABSTRACT FROM AUTHOR]

Highlights • Experimental Estimation of diffusion length of Ga adatoms on GaP (0 0 1) • Correlation between the behavior of diffusion length and surface morphology as a function of the temperature. • Observation of anisotropy along < 1 1 ¯ 0 > and < 1 1 ¯ 0 > directions. Abstract In this work Ga adatom incorporation diffusion length was quantified in two different directions, 〈1 1 0〉 and < 1 1 ¯ 0 > , during MBE growth of a GaP layer. Thickness distribution was measured for the GaP layer grown on striped patterned GaP substrate and the data was analyzed based on a one-dimensional diffusion growth model between two different adjacent facets. It was quantitatively revealed that the diffusion length of the Ga adatoms increased with growth temperature and an anisotropy in the diffusion length was observed along < 110 > and < 1 1 ¯ 0 > directions. The influence in the morphology due to the diffusion length anisotropy was discussed with the RHEED patterns. [ABSTRACT FROM AUTHOR]

Highlights • MBE growth of carbon doped GaAs-(1 1 1)B layers on a miscut substrate. • Carbon doping concentration from 10 16 c m -3 to 10 20 c m -3 • Smooth GaAs(1 1 1)B surfaces (RMS 0.3 nm) up to N C 10 20 c m -3 were achieved. • p-type behavior and electrically active donor incorporation up to N C ≤ 10 19 c m -3. • The carbon ionization energy in GaAs(1 1 1)B was determined to E A = 26.3 ± 0.1 meV. Abstract Here we present a study of the solid source molecular beam epitaxy growth of carbon doped GaAs(1 1 1)B oriented layers in a wide doping concentration range from 10 16 to 10 20 cm - 3 . The layers have been fabricated on GaAs(1 1 1)B substrates with a 1° miscut towards (2 1 1) and carbon was supplied by a heated graphite filament source. Atomic force microscopy revealed smooth surfaces (root mean square roughness 0.3 nm) up to the highest carbon concentration. The carbon concentration was determined by secondary ion mass spectroscopy. All samples exhibit p-type conductivity and temperature-dependent Hall- and resistivity measurements show carrier freeze out for doping concentration in the 10 16 cm−3 and 10 17 cm−3 range, whereas we observe degenerated behavior for carbon concentrations above ca. 1 × 10 19 cm−3. The hole mobility decreases with increasing carbon concentration. The acceptor ionization energy for carbon was determined via low-temperature photoluminescence measurements to 26.3 meV. From the free hole density determined from Hall-measurements at 300 K and the overall carbon concentration, we estimate that approximately 100% of the carbon atoms are electrically active acceptors for carbon concentrations below 1 × 10 18 cm−3. For concentrations above 1 × 10 19 cm−3 compensation sets in and the doping efficiency is well below 100%. For comparison, samples in the standard (1 0 0)-orientation have been produced and carbon incorporation behavior during growth is very similar. [ABSTRACT FROM AUTHOR]

Highlights • In-plane InSb nanostructures are grown using atomic hydrogen assisted MBE. • InSb selective area epitaxy with respect to a SiO 2 mask is achieved. • Long in-plane nanowires are obtained despite lattice mismatch for narrow apertures. • InSb nanowire MOSFET with 1 µm gate length are fabricated without any transfer. Abstract The selective molecular beam epitaxy of InSb inside nanoscale apertures realized in a SiO 2 mask deposited on a highly mismatched substrate is studied. The substrate of interest is GaAs on which a 6.1 Å material (InAs or AlGaSb) has been grown accommodating part of the mismatch with InSb. For sub-100 nm wide aperture, several micron long in-plane InSb nanowires can be obtained. Different ways for measuring the electrical properties of these in-plane nanostructures are proposed. A 1 µm long gate length MOSFET is fabricated on a semi-insulating AlGaSb pseudo-substrate without any transfer on a host substrate. [ABSTRACT FROM AUTHOR]

Highlights • Lattice deformations in InGaAs/GaAs(1 1 1)A were studied by in situ RSM. • Anomalous lattice shrinkage along the c-axis was found in InGaAs/GaAs(1 1 1)A. • InGaAs/InAs/GaAs(1 1 1)A structure effectively improved crystal quality of InGaAs. Abstract Using in situ synchrotron X-ray reciprocal space mapping, this study investigates the evolution of lattice deformations in the InGaAs/GaAs(1 1 1)A structure with or without a thin InAs layer grown by molecular beam epitaxy. During the initial growth phase, InGaAs directly grown on GaAs(1 1 1)A showed an anomalous lattice shrinkage along the c-axis, with no change in the indium composition. Conversely, the InGaAs grown on InAs/GaAs(1 1 1)A showed no initial lattice distortion, but a variable indium composition. The evolution of the diffraction peak broadening was also monitored. The results confirmed that the thin InAs layer effectively improved the crystal quality during the initial growth of InGaAs. [ABSTRACT FROM AUTHOR]

Highlights • In 0.74 Ga 0.26 As detector structures with superlattice barrier are grown on InP. • The effects of barrier thickness and period number are investigated. • Dark currents are reduced for the moderate barrier thickness and period number. • Excessive barrier thickness and period number induce material deterioration. Abstract The effects of thickness and period number of In 0.6 Ga 0.4 As/InAs superlattice electron barrier on the performances of InP-based metamorphic In 0.74 Ga 0.26 As detectors have been investigated. The samples were grown by molecular beam epitaxy and characterized by high resolution X-ray diffraction reciprocal space maps, photoluminescence, atomic force microscope, plan view transmission electron microscopy and the device dark current measurements. Results show that the dark currents are reduced by insertion of an electron barrier with moderate thickness and period number in the absorption layer, but a superlattice electron barrier structure with excessive thickness and period number can lead to the deterioration of the material quality and device performances. [ABSTRACT FROM AUTHOR]

Highlights • Investigation of magnetic properties of GaMnAsP films with two different thicknesses. • The Curie temperature was higher in thicker GaMnAsP layer. • Annealing increases the Curie temperature of GaMnAsP layers. • The out-of-plane magnetic anisotropy becames stronger after annealing. • 3-D magnetic anisotropy energy diagrams show easy axes of GaMnAsP films. Abstract We have investigated the magnetic properties of ferromagnetic semiconductor GaMnAsP films with two different thicknesses. Temperature scans of the resistance revealed that the Curie temperature was higher in the 50-nm GaMnAsP layer than in the 16-nm layer, and was increased in both layers after annealing. The Hall effect was measured during the magnetization reversal process to identify the anisotropy of the films. The hysteresis observed from the as-grown samples in anomalous Hall resistance measurements implied the presence of out-of-plane magnetic anisotropy in both samples. The out-of-plane magnetic anisotropy in both samples became much stronger after thermal annealing. Quantitative values of the magnetic anisotropy of the GaMnAsP films were obtained from angular dependent Hall effect measurements. By constructing magnetic anisotropy energy diagrams for the films, we clearly show the change of magnetic anisotropy depending on the film thickness and thermal annealing in GaMnAsP films. [ABSTRACT FROM AUTHOR]

Highlights • In-plane InGaAs nanowires are grown using selective area molecular beam epitaxy. • Growth selectivity is achieved at 470 °C thanks to an atomic hydrogen flux. • High quality InGaAs thin films grown on InP without a buffer layer are achieved. Abstract We investigate the optical and electrical properties of InGaAs thin films and nanostructures grown directly on an InP semi-insulating substrate without any buffer layer using atomic hydrogen assisted molecular beam epitaxy. We confirm the positive influence of the atomic hydrogen flux during the deoxidization process as well as during the growth itself improving the photoluminescence properties of InGaAs quantum wells. We also study the effect of the atomic hydrogen flux on the electrical properties of buffer free undoped, Te or Si doped InGaAs epilayers. Eventually, we demonstrate that atomic hydrogen flux can be used to achieve InGaAs growth selectivity with respect to a SiO 2 mask for a growth temperature as low as 470 °C and obtain in-plane InGaAs nanostructures on InP with good transport properties. [ABSTRACT FROM AUTHOR]

Highlights • Nitrogen-rich growth of high quality and uniform nitride heterostructures in plasma-assisted MBE. • Use of high miscut angle bulk (0 0 0 1 ¯) GaN substrates to obtain atomically smooth interfaces in quantum wells. • Improved optical and crystal quality for epitaxy on higher miscut angle substrates. • Proof for much higher indium incorporation for N-polar than for Ga-polar quantum wells. • Cathodoluminescence, Photoluminescence, X-ray diffraction and atomic force microscopy data are compared. Abstract New growth window for N-polar nitride devices is reported for plasma-assisted molecular beam epitaxy (PAMBE). Nitrogen-rich growth conditions were employed to obtain good optical quality N-polar (0 0 0 1 ¯) InGaN/GaN heterostructures. Atomically flat interfaces were obtained for N-rich growth on (0 0 0 1 ¯) GaN substrates with high miscut angle of 4° and 7°. Ga-polar samples grown at the same growth conditions were rough and exhibit no indium incorporation. Obtained results point out significantly different growth kinetics on both GaN polarities and offer efficient way for fabricating N-polar devices by PAMBE. [ABSTRACT FROM AUTHOR]

Highlights • Systematical investigation of the crystal growth of BiSb thin films on GaAs(1 1 1)A, GaAs(1 1 1)B, and GaAs(0 0 1) substrates. • Non-trivial growth mode of BiSb. • Growth depends not only on the crystal orientation but also on the surface termination of GaAs. • Hints for future integration of BiSb thin films to realistic spin devices. Abstract We investigate the crystal growth of BiSb thin films on various GaAs substrates with different crystal orientation and surface termination. We found the non-trivial growth mode of BiSb which depends on the crystal orientation/surface termination of GaAs. While BiSb(0 0 1) can be grown epitaxially on GaAs(1 1 1)A, only textured BiSb(0 1 2) can be grown on GaAs(1 1 1)B even with the help of an ultrathin Bi buffer layer, indicating the critical role of surface termination of the GaAs(1 1 1) substrates. Meanwhile, only textured BiSb(0 0 1) thin films grow on GaAs(0 0 1) instead of BiSb(0 1 2), indicating that symmetry matching plays a little role on the growth of BiSb on GaAs(0 0 1). [ABSTRACT FROM AUTHOR]

Highlights • Two-dimensional (2D) film formation in group-III nitrides is theoretically studied. • There is faint charge between III-nitrides with 2D structure and Ag(1 1 1) substrate. • The lattice constraint is negligible for III-nitride with hexagonal structure. • The hexagonal structure is stabilized up to 15 monolayers due to interlayer interactions. Abstract The formation of two-dimensional (2D) ultrathin films in III-nitride compound on Ag(1 1 1) substrate is investigated using density functional calculations. The calculations demonstrate that there is faint charge distribution between III-nitrides with 2D hexagonal structure and Ag(1 1 1) substrate while metallic bonds are formed at the interface for III-nitrides with wurtzite structure. This indicates that the lattice constraint of Ag(1 1 1) substrate is negligible for III-nitride compound ultrathin films with hexagonal structure. Furthermore, the hexagonal structure is more stable than wurtzite phase for the films up to 15 monolayers due to interlayer electrostatic interactions. The results suggests that various 2D III-nitride compound ultrathin films can be formed on Ag(1 1 1) substrate. [ABSTRACT FROM AUTHOR]

Highlights • Direct growth of MnSe and MnTe on GaAs (0 0 1) only results in their stable phases. • Zinc-blende MnSe 1−x Te x thin films were fabricated via a ZnTe buffer. • The thin film effect on the distortion of the alloy lattice has been addressed. • A MnSe 1−x Te x /ZnTe heterostructure with perfect lattice match has been achieved. • It shines light for realizing a THz emitter based on a new lattice-matched system. Abstract We report studies on the role of a ZnTe buffer in determining the crystalline phase of MBE-grown MnSe 1−x Te x alloy thin films. It was found that MBE growth of MnSe and MnTe directly onto a zincblende GaAs substrate usually result in their corresponding stable phases, which are rocksalt and hexagonal, respectively. A set of zincblende MnSe 1−x Te x alloy thin films with Te composition covering from 0.27 to 1 were fabricated on zincblende ZnTe buffer layers. We have addressed the lattice distortion issue due to thin film effect for these films. A combination of several structural characterizations demonstrates that a perfect lattice matched MnSe 1−x Te x /ZnTe heterostructure can indeed be realized. The results of this study pave the way for realizing a double-barrier MnSe 1−x Te x /ZnTe/MnSe 1−x Te x resonant tunneling diode structure with perfect lattice match as a candidate for a promising THz emitter. [ABSTRACT FROM AUTHOR]

Highlights • Zinc blende MnS layers were grown on GaAs(1 0 0) substrates. • Zinc blende MnS layers up to 250 nm thick produced. • X-ray diffraction and interference techniques used for characterisation. • A phase diagram for ZB MnS giving zinc incorporation has been produced. Abstract MnS has been grown by molecular beam epitaxy in the metastable zinc blende (ZB) crystal structure on GaAs (1 0 0) substrates using ZnS as a sulphur source. MnS layers were grown over a wide range of growth conditions by varying the growth temperature from 220 °C to 300 °C and ZnS:Mn flux ratio from 5 to 20. Double-crystal X-ray rocking curves were used to determine the crystallinity and residual zinc content in the layers. This allowed a phase diagram to be produced for ZB MnS giving zinc incorporation as function of the growth temperature and the ZnS:Mn beam flux ratio. In turn, this allowed an optimum growth region to be identified at a growth temperature 240 °C and ZnS:Mn flux ratio 6 where ZB MnS with less than 1% residual zinc incorporation were obtained. Under these optimum growth conditions the maximum ZB MnS layer thickness obtained was double that obtained in previous studies, with layers up to 250 nm thick produced. [ABSTRACT FROM AUTHOR]

Highlights • Epitaxial growth of Fe delta-doped (In,Fe)Sb thin films. • Intrinsic ferromagnetism confirmed by MCD spectroscopy measurements. • T C lower than the uniformly-doped (ln,Fe)Sb with the same average Fe concentration. • Much higher Hall sensitivity of the δ-doped samples than those of uniformly-doped. • Very promising for highly sensitive anomalous Hall effect sensors. Abstract We have grown Fe δ-doped (In,Fe)Sb thin films by low-temperature molecular beam epitaxy for magnetic-field sensors with ultrahigh Hall sensitivity. Magnetic circular dichroism spectroscopy measurements indicate intrinsic ferromagnetism in the Fe δ-doped (In,Fe)Sb layers. Although the Fe δ-doped (In,Fe)Sb thin films have lower Curie temperature than the Fe uniformly-doped (ln,Fe)Sb with the same average Fe concentration, their anomalous Hall effect is much stronger. The Hall sensitivity of the Fe δ-doped (In 1−〈 x 〉 ,Fe 〈 x 〉)Sb sample with an average Fe concentration 〈 x 〉 = 17% reaches 1522 Ω/T at room temperature, which is much higher than those of Fe uniformly-doped (In,Fe)Sb, (Ga,Fe)Sb, and commercial InSb Hall sensors. [ABSTRACT FROM AUTHOR]

Highlight • III-V laser monolithically integrated on a CMOS-compatible Si substrate. • MBE-grown InAs/GaAs quantum dot laser on Si with low threshold current density (160 A/cm2) • Single facet output power of 48 mW at injection current density of 500 A/cm2 at room temperature. • Laser operation up to 52 °C under continuous-wave operation mode with characteristic temperature of 60.8 K. Abstract The concept of high-efficiency, high-reliability and low-threshold electrically pumped lasers monolithically grown on silicon has attracted great attention over the past several decades, as a promising on-chip optical source for Si photonics. In this paper, we report an electrically pumped continuous-wave (CW) 1.3 µm InAs/GaAs quantum dot (QD) lasers grown on a complementary metal-oxidesemiconductor (CMOS) compatible Si exact (0 0 1) substrate with reduced GaAs buffer thickness down to ∼2 µm. A threshold current density (J th) as low as ∼160 A/cm2 has been achieved at room temperature. The characteristic temperature (T 0) obtained is ∼60.8 K and laser operation is observed up to 52 °C under CW mode. These results suggest that an O-band InAs/GaAs QD laser could be very promising to develop a monolithically integrated on-chip optical source for Si photonics. [ABSTRACT FROM AUTHOR]

Highlights • Methodology to determine flux and temperature distributions for stationary MBE. • GaAsBi growth regimes determined in high resolution with respect to the As/Ga ratio. • Strong variation of Bi incorporation and structural properties. • Material optimization by fine-tuning the As/Ga ratio. Abstract The control of Bi incorporation and material properties in III-V-Bi alloys has proved challenging due to their high sensitivity to the epitaxial growth parameters. Here, we present a methodology for determining the variation in the Ga, As, and Bi fluxes and the temperature across a stationary substrate in molecular beam epitaxy. By correlating the flux distributions with material properties, we identify distinct regimes for epitaxy of GaAsBi. In particular, we devise a detailed image of the interplay between Bi incorporation and structural properties of a bulk GaAs 0.96 Bi 0.04 layer grown on GaAs(1 0 0) with respect to the As/Ga ratio. The influence of As/Ga is analyzed with high resolution over the important stoichiometric range (i.e. As/Ga = 0.6–1.6). Growth outside the near-stoichiometric As/Ga regime leads to decreased Bi incorporation, decreased structural quality and the formation of Ga, Ga/Bi or Bi droplets. On the other hand, growth at As/Ga = 1.00–1.17 leads to maximized material quality. For this regime, the surface roughness is further optimized by fine-tuning the As/Ga ratio to suppress surface mounding to a value of 0.5 nm. The results reveal the extreme sensitivity of GaAsBi growth to small variations in the As/Ga ratio, and demonstrate the applicability of stationary growth in studying these effects. [ABSTRACT FROM AUTHOR]

Graphical abstract Growth of self-assembled and position-controlled InN nanowires on Si (1 1 1) substrates by plasma-assisted molecular beam epitaxy is demonstrated. By variation of the growth parameters, fundamental knowledge of the nanowire formation process is obtained. Structural analysis of a self-assembled InN nanowire reveals that the nanowire has a wurtzite crystal structure covered by an indium oxide shell. In addition, it is shown that self-assembled InN nanowires can exhibit both lattice polarities. Highlights • Decomposition and redeposition effects dominate at high growth temperatures. • Self-assembled InN NW exhibits wurtzite crystal structure covered by an oxide shell. • Self-assembled InN NWs show both lattice polarities. • Growth of position-controlled InN NWs on different substrates possible. Abstract This work presents a systematic growth study of self-assembled and position-controlled InN nanowires (NWs) on Si (1 1 1) substrates by plasma-assisted molecular beam epitaxy without using a buffer layer. By variation of the substrate temperature, the III/V flux ratio, and the growth time, optimal parameters for self-assembled and position-controlled NW growth are found and compared. This leads to a fundamental understanding of the underlying growth mechanism for InN NW formation. Scanning transmission electron microscopy measurements of a self-assembled InN NW show a wurtzite crystal structure with a hexagonal cross-section and flat lateral facets covered by an approximately 5 nm thick indium oxide shell. In addition, Kelvin probe force microscopy measurements indicate the existence of both lattice polarities in case of self-assembled InN NWs. [ABSTRACT FROM AUTHOR]

Highlights • Efficient Fe doping into GaN buffer layer achieved using solid Fe source in NH 3 MBE growth. • Semi-insulating (S.I.) GaN buffer is realized by adding Fe impurities. • The increased sites occupied by too many Fe atoms will damage the lattice order. • Unnecessary Fe dopants over 1019 cm−3 tends to increase the residual stress. Abstract The electrical properties of AlGaN/GaN high electron mobility transistor structures with composite Fe-doped GaN/undoped GaN buffers grown on (1 1 0) Si substrates by ammonia molecular beam epitaxy were reported. Fe concentration in the range of 1017 cm−3 is sufficient to compensate the residual donors (<1016 cm−3) of undoped GaN and demonstrated a highly resistive GaN on (1 1 0) Si substrates. For buffers with Fe concentration of 1 × 1017 ∼ 1 × 1018 cm−3, the buffer was semi-insulating, with the Fermi level pinned near 0.5–0.7 eV which is determined by temperature-dependent I-T measurements. From the PICTS measurements, the Fe-related peaks of 0.69 eV (B) and 0.86 eV (C) are observed. The peak B is most likely due to the center pinning the Fermi level which is close to the activation energy observed in the temperature-dependent current measurement of Fe-doped sample, tentatively attributed to complexes between substitutional Fe ions and native defects such as nitrogen vacancies. The peak C is similar to the hole trap of 0.85 eV previously reported. In spite of similar transfer device characteristics, the Fe-doped buffer shows a noticeable difference in the off-state leakage behaviors. The sample grown with the optimized Fe concentration of 1 × 1017 cm−3 had a buffer resistivity of approximately 3.84 × 1011 Ω cm, increased by almost four orders of magnitude with respect to that (4.5 × 107 Ω cm) of the reference sample with undoped GaN buffer. [ABSTRACT FROM AUTHOR]

Highlights • Plasma-assisted molecular beam epitaxy of AlGaN-based multiquantum wells with ∼280 nm emission. • Structural characterization and modeling of interface roughness of the AlGaN wells and barriers. • Optical characterization of the AlGaN materials. Abstract We have investigated the nature of Al 0.56 Ga 0.44 N/Al 0.62 Ga 0.38 N multiquantum wells grown by plasma-assisted molecular beam epitaxy for application in deep-ultraviolet light emitters. Excitation and temperature-dependent and time-resolved photoluminescence measurements and transmission and reflectance spectroscopy have been complemented by high-angle annular dark field scanning transmission electron microscopy. The 3 nm quantum wells are characterized by interface roughness having a height of 0.3–1 nm and the maximum value is in excellent agreement with values obtained from calculations done to analyze the measured photoluminescence lineshape. The radiative lifetime increases with temperature, suggesting the role of electron-hole scattering to cool photoexcited carriers to the ground state of the quantum wells. [ABSTRACT FROM AUTHOR]

Highlights • Epitaxial regrowth accomplished on a membrane that was removed from its native substrate. • Power-dependent photoluminescence shows comparable recombination rates versus baseline. • Cathodoluminescence map indicates uniform bulk crystal quality on membrane epitaxy. Abstract Micro-transfer printing has demonstrated value for device- and array-level heterogeneous integration in a variety of applications. Here, it is used instead to assemble unique substrates with the potential to enable III–V growth templates that are both low-cost and specified at any desired lattice parameter within the range of III–V materials. Critical to this, epitaxial growth crystal quality must be established as comparable to that produced on conventional epi-ready substrates. We demonstrate epitaxial regrowth on gallium arsenide membranes that were transfer printed from their source substrate and onto a target handle. Both morphology and luminescence properties were characterized. Comparing the transfer printed membrane epitaxy with epitaxy on a conventional substrate, we found recombination rates and spatial uniformity from power-dependent photoluminescence and cathodoluminescence, respectively, to yield similar results, suggesting material quality was not adversely limited by the engineered substrate. [ABSTRACT FROM AUTHOR]

Highlights • Mn 4−x Ni x N films were grown on MgO(0 0 1) by molecular beam epitaxy. • The saturation magnetization (M S) and perpendicular magnetic anisotropy diminished with a small amount of Ni substitution. • The M S value was remarkably decreased from 86 emu/cm3 (Mn 4 N) to 19 emu/cm3 (Mn 3.75 Ni 0.25 N). • Magnetic anisotropy constants of 0.94 and 0.027 Merg/cm3 were obtained, respectively. Abstract We grew Mn 4− x Ni x N epitaxial thin films on MgO(0 0 1) by molecular beam epitaxy, as well as studied their crystalline qualities and magnetic properties. The films were decomposed into Ni 8 N or Mn-Ni alloys when x ≥ 2, as confirmed by X-ray diffraction and reflection high-energy electron diffraction, but this decomposition was mitigated by reducing the substrate growth temperature. The lattice constants decreased with increased Ni substitution except when the Mn ratio was high, while the crystal orientation tended to degrade. The magnetic properties were measured via vibrating sample magnetometer, and it was found that the saturation magnetization (M S) and perpendicular magnetic anisotropy (PMA) diminished with a small amount of Ni substitution. Specifically, the M S value was remarkably decreased from 86.3 ± 1.1 emu/cm3 (Mn 4 N) to 19.0 ± 0.5 emu/cm3 (Mn 3.85 Ni 0.25 N), and the magnetic anisotropy constant was decreased from approximately 0.94–0.027 Merg/cm3, respectively. The PMA vanished with further Ni substitution. Ultimately, a small M S and a PMA were simultaneously achieved with a small amount of Ni substitution. These properties support spin transfer torque, which can be applied to the emerging non-volatile memory devices using domain wall motion. [ABSTRACT FROM AUTHOR]

Highlights • AlN and GaN films were grown on Silicon by plasma assisted molecular beam epitaxy. • Metal-rich growth conditions can induce peculiar defects. • The defects consist of crystallites connected with buried patterns. • Ga or Al may have diffused through AlN nucleation layer to react with Silicon. Abstract The present work is dedicated to the study of peculiar defects observed in GaN/AlN structures grown on Silicon substrate using the plasma assisted Molecular Beam Epitaxy under metal-rich conditions. Optical microscopy shows that these defects have undefined shape when AlN is grown on Silicon. On the contrary such defects are not observed with AlN films grown under nitrogen-rich plasma assisted or ammonia source Molecular Beam Epitaxy, but triangular shape defects appear in case of GaN regrowth on the latter. As scanning electron microscopy is not able to evidence these defects but only protuberances connected with them, we deduce that they are located in the Silicon substrate. Complementary analysis with atomic force microscopy and energy dispersive X-ray analysis lead us to propose a scenario involving the etching of the Silicon substrate with Ga or Al diffusing through weak points in the nucleation layer. [ABSTRACT FROM AUTHOR]

Highlights • Molecular beam epitaxy of AlGaN epilayers on AlN template on sapphire substrate. • Effects of growth parameters on tuning the Al composition in AlGaN are studied. • Atomically smooth Al0.6Ga0.4N obtained under slightly metal-rich conditions. • Dislocation propagation from the substrate reduced by incorporating sub-nm interfaces. Abstract We have performed a detailed investigation of the molecular beam epitaxy of AlGaN epilayers on AlN template on sapphire substrate. The effects of various growth parameters, including nitrogen flow rate, and Al and Ga fluxes on tuning the Al composition of these epilayers are studied. An atomically smooth surface with a root mean square roughness of ∼0.4 nm was measured for ∼0.5-μm thick Al 0.6 Ga 0.4 N when grown under slightly metal-rich conditions. It was observed that dislocation propagation originating from the substrate layers can effectively be reduced or terminated in AlGaN epilayers with the incorporation of sub-nm interfaces. A refractive index contrast of 0.09 with the underlying AlN template was measured at a wavelength of 400 nm, making it suitable for waveguiding applications. [ABSTRACT FROM AUTHOR]