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GaAs/AlGaAs core-shell nanowires, typically having 250 nm diameter and 6 mu m length, were grown on 2-inch Si wafers by the single process of molecular beam epitaxy using constituent Ga-induced self-catalysed vapor-liquid-solid growth. The growth was carried out without specific pre-treatment such as film deposition, patterning, and etching. The outermost Al-rich AlGaAs shells form a native oxide surface protection layer, which provides efficient passivation with elongated carrier lifetime. The 2-inch Si substrate sample exhibits a dark-colored feature due to the light absorption of the nanowires where the reflectance in the visible wavelengths is less than 2%. Homogeneous and optically luminescent and adsorptive GaAs-related core-shell nanowires were prepared over the wafer, showing the prospect for large-volume III-V heterostructure devices available with this approach as complementary device technologies for integration with silicon.

Energy upconversion via optical processes in semiconductor nanowires (NWs) is attractive for a variety of applications in nano-optoelectronics and nanophotonics. One of the main challenges is to achieve a high upconversion efficiency and, thus, a wide dynamic range of device performance, allowing efficient upconversion even under low excitation power. Here, we demonstrate that the efficiency of energy upconversion via two-photon absorption (TPA) can be drastically enhanced in core/shell NW heterostructures designed to provide a real intermediate TPA step via the band states of the narrow-bandgap region with a long carrier lifetime, fulfilling all the necessary requirements for high-efficiency two-step TPA. We show that, in radial GaAs(P)/GaNAs(P) core/shell NW heterostructures, the upconversion efficiency increases by 500 times as compared with that of the constituent materials, even under an excitation power as low as 100 mW/cm2 that is comparable to the 1 sun illumination. The upconversion efficiency can be further improved by 8 times through engineering the electric-field distribution of the excitation light inside the NWs so that light absorption is maximized within the desired region of the heterostructure. This work demonstrates the effectiveness of our approach in providing efficient photon upconversion by exploring core/shell NW heterostructures, yielding an upconversion efficiency being among the highest reported in semiconductor nanostructures. Furthermore, our work provides design guidelines for enhancing efficiency of energy in NW heterostructures. Funding Agencies|Swedish Research Council [2019-04312]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; KAKENHI from the Japan Society for the Promotion of Science [16H05970, 19H00855, 21KK0068]; Japan Society for the Promotion of Science

GaAs/GaNAsBi/GaAs core–multishell nanowires were grown using molecular beam epitaxy on Si(111) substrates. The formation of the 20 nm-wide GaNAsBi shell with a regular hexagonal structure was observed. The shell is estimated to contain approximately 1.5% N and 2.6% Bi and has a compressive lattice mismatch of less than 0.2 % with GaAs layers. The strain mediation by the introduction of both N and Bi suppresses the crystalline deformation, resulting in the clear formation of the GaNAsBi shell. Thus, we obtained room-temperature photoluminescence with the maximum position at approximately 1300 nm from the GaAs/GaNAsBi/GaAs core–multishell nanowires.

Deep-ultraviolet continuous-wave photoluminescence spectroscopy is performed for nano-polycrystalline diamond (NPD) synthesized by a high pressure high-temperature technique. NPD exhibits clear dee...

We control the formation of Bi-induced nanostructures on the growth of GaAs/GaAsBi core-shell nanowires (NWs). Bi serves as not only a constituent but also a surfactant and nanowire growth catalyst. Thus, we paved a way to achieve unexplored III-V nanostructures employing the characteristic supersaturation of catalyst droplets, structural modifications induced by strain, and incorporation into the host GaAs matrix correlated with crystalline defects and orientations. When Ga is deficient during growth, Bi accumulates on the vertex of core GaAs NWs and serves as a nanowire growth catalyst for the branched structures to azimuthal112. We find a strong correlation between Bi accumulation and stacking faults. Furthermore, Bi is preferentially incorporated on the GaAs (112)B surface, leading to spatially selective Bi incorporation into a confined area that has a Bi concentration of over 7%. The obtained GaAs/GaAsBi/GaAs heterostructure with an interface defined by the crystalline twin defects in a zinc-blende structure can be potentially applied to a quantum confined structure. Our finding provides a rational design concept for the creation of GaAsBi based nanostructures and the control of Bi incorporation beyond the fundamental limit.

GaAs-based semiconductors are highly attractive for diverse nonlinear photonic applications, owing to their non-centrosymmetric crystal structure and huge nonlinear optical coefficients. Nanostructured semiconductors, for example, nanowires (NWs), offer rich possibilities to tailor nonlinear optical properties and further enhance photonic device performance. In this study, it is demonstrated highly efficient second-harmonic generation in subwavelength wurtzite (WZ) GaAs NWs, reaching 2.5 × 10−5 W−1, which is about seven times higher than their zincblende counterpart. This enhancement is shown to be predominantly caused by an axial built-in electric field induced by spontaneous polarization in the WZ lattice via electric field-induced second-order nonlinear susceptibility and can be controlled optically and potentially electrically. The findings, therefore, provide an effective strategy for enhancing and manipulating the nonlinear optical response in subwavelength NWs by utilizing lattice engineering. Funding: Swedish Research Council European Commission [2019-04312]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University [2009 00971]; KAKENHI from Japan Society of Promotion of Science [19H00855, 16H05970]; National Natural Science Foundation of China (NSFC) [12027805, 11991060]

III-V semiconductor nanowires (NWs), such as those based on GaAs, are attractive for advanced optoelectronic and nanophotonic applications. The addition of Bi into GaAs offers a new avenue to enhance the near-infrared device performance and to add new functionalities, by utilizing the remarkable valence band structure and the giant bowing in the bandgap energy. Here, we report that alloying with Bi also induces the formation of optically-active self-assembled nanodisks caused by Bi segregation. They are located in the vicinity to the (112) corners of the GaAsBi shell and are restricted to twin planes. Furthermore, the Bi composition in the disks is found to correlate with their lateral thickness. The higher Bi composition in the disks with respect to the surrounding matrix provides a strong confinement for excitons along the NW axis, giving rise to narrow emission lines (Funding Agencies|Swedish Research CouncilSwedish Research Council [2019-04312]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; KAKENHI from Japan Society of Promotion of Science [19H00855, 16H05970]

Core/shell nanowire (NW) heterostructures based on III-V semiconductors and related alloys are attractive for optoelectronic and photonic applications owing to the ability to modify their electronic structure via bandgap and strain engineering. Post-growth thermal annealing of such NWs is often involved during device fabrication and can also be used to improve their optical and transport properties. However, effects of such annealing on alloy disorder and strain in core/shell NWs are not fully understood. In this work we investigate these effects in novel core/shell/shell GaAs/GaNAs/GaAs NWs grown by molecular beam epitaxy on (111) Si substrates. By employing polarization-resolved photoluminescence measurements, we show that annealing (i) improves overall alloy uniformity due to suppressed long-range fluctuations in the N composition; (ii) reduces local strain within N clusters acting as quantum dot emitters; and (iii) leads to partial relaxation of the global strain caused by the lattice mismatch between GaNAs and GaAs. Our results, therefore, underline applicability of such treatment for improving optical quality of NWs from highly-mismatched alloys. They also call for caution when using ex-situ annealing in strain-engineered NW heterostructures. Funding Agencies|Swedish Energy AgencySwedish Energy Agency [P40119-1]; Swedish Research CouncilSwedish Research Council [2015-05532]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; KAKENHI from the Japan Society for the Promotion of ScienceMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) [16H05970, 23686004]; Kato Foundation for Promotion of Science; Kurata Memorial Hitachi Science and Technology Foundation; Murata Science Foundation; Linkoping University

We investigated inherent electronic properties of ultra-hard nano-polycrystalline diamond (NPD) synthesised at 15 GPa and 2300 °C. NPD exhibited a p-type semiconducting property with a resistivity of 1 × 10 6 and 4 × 10 2 Ω cm at 400 °C and 800 °C, respectively, with activation energies as high as 1.2 eV. The mobility was 2 cm 2 /Vs at 800 °C. The observed transport was considered to be attributed to grain boundary. Cathodoluminescence spectra show defect-related peaks with dominant peaks at 2.8 eV close to band-A and peaks below 2 eV, which is possibly related to crystal defects. In contrast, photoluminescence excited with a wavelength of 405 nm resonantly excited peaks having energies lower than 2.1 eV. The large density of crystalline defects such as grain boundaries and impurities in the NPD would result in the characteristic electronic and optical properties.

We obtain white luminescence by the oxidation of GaAs/Al-rich Al0.87Ga0.13As nanowire which is visible to the eye. The oxidized amorphous AlGaOx shell emits light over a wide spectral range covering entire visible wavelengths between 400–700 nm. The emission intensity depends on the oxidation temperature and time. Through the optimization of those conditions, we observe clear white light from the sample by the eye under the illumination of ultraviolet light-emitting diodes, which would be applicable as a white light phosphor.

Eleven periods of GaAsBi/GaAs multiple quantum wells (MQWs) on (100) GaAs substrates were grown by molecular beam epitaxy (MBE) using the two-substrate-temperatures (TST) technique. In the TST technique, the substrate temperature was set at T GaAsBi = 350 °C for GaAsBi layers and T GaAs = 550 °C for GaAs layers for the growth of MQWs. The structural and optical characterization of GaAsBi/GaAs MQWs using TST technique was carried out for growth optimization by changing As 4 /Ga beam equivalent pressure (BEP) ratio. Atomic force microscope observation shows high As 4 /Ga BEP ratio supply can prevents roughening of the GaAsBi layer surface of MQWs. High resolution x-ray diffraction analysis results reveal Bi incorporation enhancement with increasing As 4 /Ga BEP ratio. The reciprocal space mapping shows highly strained MQWs layers can be grown without relaxation with respect to the GaAs substrate at optimized growth conditions. At room temperature 1.22 μm photoluminescence emission was obtained from GaAs 0.962 Bi 0.038 /GaAs MQWs grown using TST technique.

Multi-quantum wells (MQWs) of GaAsBi/GaAs were grown by molecular beam epitaxy (MBE) and dependence of its surface morphology, Bi content and optical properties on Bi beam equivalent pressure (BEP) were studied. For the MQWs growth, two-substrate-temperatures (TST) technique was used, where GaAsBi layers were grown at T GaAsBi = 350 °C and GaAs layers at T GaAs = 550 °C. The segregated bismuth atoms were desorbed by increasing the substrate temperature from T GaAsBi to T GaAs after finishing the growth of each GaAsBi layer of MQWs including the topmost GaAsBi layer. The surface of the topmost GaAsBi layer shows no sign of Bi droplet formation even for the MQWs grown at highest Bi supply. The Bi content increases up to 3.8% in proportional to the Bi BEP and decreases in a higher Bi BEP region.

We demonstrate the molecular beam epitaxial growth of high quality GaAs/GaNAs/GaAs core-multishell nanowire containing 2% nitrogen in the GaNAs shell layer. The transmission microscopy investigation shows clear formation of the core-multishell structure without detectable deformations. We observe lasing peak near $1 \mu \mathrm{m}$ sustaining its lasing behavior up to over 100 K. These results demonstrate that the utilized structure represents a promising alternative for achieving room-temperature near-infrared nanowire lasers.

Nanowire (NW) lasers operating in the near infrared spectral range are of significant technological importance for applications in telecommunications, sensing, and medical diagnostics. So far, lasing within this spectral range has been achieved using GaAs/AlGaAs, GaAs/GaAsP, and InGaAs/GaAs core/shell NWs. Another promising III-V material, not yet explored in its lasing capacity, is the dilute nitride GaNAs. In this work, we demonstrate, for the first time, optically pumped lasing from the GaNAs shell of a single GaAs/GaNAs core/shell NW. The characteristic "S"-shaped pump power dependence of the lasing intensity, with the concomitant line width narrowing, is observed, which yields a threshold gain, g(th), of 3300 cm(-1) and a spontaneous emission coupling factor beta, of 0.045. The dominant lasing peak is identified to arise from the HE21b, cavity mode, as determined from its pronounced emission polarization along the NW axis combined with theoretical calculations of lasing threshold for guided modes inside the nanowire. Even without intentional pas sivation of the NW surface, the lasing emission can be sustained up to 150 K. This is facilitated by the improved surface quality due to nitrogen incorporation, which partly suppresses the surface-related nonradiative recombination centers via nitridation. Our work therefore represents the first step toward development of room-temperature infrared NW lasers based on dilute nitrides with extended tunability in the lasing wavelength. Funding Agencies|Swedish Energy Agency [P40119-1]; Swedish Research Council [2015-05532]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; KAKENHI from the Japan Society for the Promotion of Science [16H05970, 23686004]; Kato Foundation for Promotion of Science; Kurata Memorial Hitachi Science and Technology Foundation; Murata Science Foundation

Eleven periods of GaAsBi/GaAs multiple quantum wells (MQWs) grown on (411)A and (411)B GaAs substrates at T GaAsBi = 350 °C and T GaAs = 550 °C by molecular beam epitaxy (MBE) and their structural and optical properties were investigated. The high resolution X-ray diffraction (HRXRD) analysis shows increment in Bi composition with the increasing As4 beam equivalent pressure (BEP). The reciprocal space mapping (RSM) reveals highly strained GaAsBi/GaAs MQWs layers can be grown without relaxation with respect to the (411) GaAs substrate on both A and B sides at an optimized growth condition of Bi and As4 BEP; while (411)A sample with higher bismuth content (5.5 %) shows lattice dislocation of MQWs due to lateral strain. The temperature-dependent photoluminescence (PL) shows 1.26 μm emission at room temperature from both the (411)A and (411)B samples for GaAs0.97Bi0.03/GaAs MQWs. It is perceived that GaAsBi/GaAs MQWS can be successfully grown on both sides of (411) GaAs substrate.

The broad visible light emission observed for GaAs/(AlGa)Ox core/shell microwires (µ wires) arises from recombination at F centers in the (AlGa)Ox shells. These µ wires are promising structures for obtaining white light emission on a Si platform. To realize efficient white light emitters it is essential to prevent the transfer of carriers to the GaAs core and the shell surface.

We investigate the activation of Sn-V centers in diamond through ions implantation and the subsequent high pressure and high temperature (HPHT) treatment at 15 GPa and 2300 °C. Sn ions is implanted at fluences greater than 2 × 1014 cm−2 by varying the acceleration voltage up to 180 kV, which results in a Sn distribution with a uniform concentration of 1 × 1020 cm−3 down to a depth of 50 nm from the surface. The subsequent HPHT treatment recovers the transparent appearance and preserves the introduced Sn ions. The sample shows emission peaks composed of four levels that originate from the Sn-V centers. The two distinct emission peaks from the lower excited states to the split ground states are stable up to 77 K. At 10 K, these peaks are clearly observable at excitation powers spanning two orders of magnitude, which suggests the preferential carrier capture at these centers.

The semiconductor photocathode with AlGaAs/GaAs superlattice structures, which is a highly durable electron beam source with low energy dispersion, were grown by molecular beam epitaxy. The sample showed a step-like quantum efficiency spectrum of photoelectron emission, indicating its applicability to photocathodes. The optimization of room temperature photoluminescence provides the improvement of the photocathode quantum efficiency up to 0.5%, promising for its further improvement and realistic applications.

We report the crystal structures of GaAs and GaAs/GaNAs/GaAs core–multishell nanowires (NWs). From statistical investigations by x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) pattern analysis, we statistically and microscopically resolve the zinc-blende (ZB) and wurtzite (WZ) polytypism within the NWs. The XRD analysis shows a smaller fraction of WZ segments in the NWs with a larger concentration of nitrogen. With increasing nitrogen content in the GaNAs shell, the ZB peak position shifts toward higher angles and the WZ peak intensity decreases. The EBSD measurements also confirm the coexistence of ZB and WZ polytypes in all of the NWs. Their polytype switches along the length. Twin defects are observed in the ZB segments in all of the NWs. The unique grain map and grain size distribution show a decrease of the WZ segments in the GaAs/GaNAs/GaAs NW, in agreement with the XRD results. Microscopically, the local area where the polytype switches from WZ in the inner-core side to ZB toward the outer-shell surface is observed. Overall, we propose that the WZ polytype in the GaAs NWs decreases because of the strain induced by the growth of the GaNAs shell with a smaller lattice constant.

We investigated microstructural deformations and Bi segregation in GaAs/GaAsBi/GaAs core–multishell heterostructures, which were triggered by the existence of twin defects. We observed Bi segregation at the interface of the twin defect interface in the GaAsBi shell. The phenomenon produced a horizontally spread Bi-accumulated nanostructure in the nanowire, which is probably induced by the large lattice mismatch between GaAs and GaAsBi. Bi is expected to penetrate through the twin defect interface, which results in the existence of Bi along twin defects and also inside the GaAs core. The existence of twin defects induced structural deformations and resulted in the formation of corrugated complex sidewall surfaces on the nanowire.

We propose native oxide AlGaO(x)outer protective layer for GaAs/AlGaAs core-multishell nanowires to provide yearly stable stronger optical and electrical confinement within the nanowire core. We prepared core-multishell NWs consisting of GaAs core, Al0.2Ga0.8As multi-layered barrier layer, and amorphous Al(0.9)Ga(0.1)O(x)outer shell, which was obtained simply by growing Al-rich AlGaAs and exposing the NWs to the ambient air. Photoluminescence from the NWs reveals that the Al(0.9)Ga(0.1)O(x)outer shell provides efficient optical confinement and creates a compressive strain in the interior of the NW that enhances and blueshifts the photoluminescence of the GaAs core. Funding Agencies|KAKENHI from Japan Society of Promotion of Science [19H00855, 16H05970]; Canon foundationCanon Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

A coherent photon source emitting at near-infrared (NIR) wavelengths is at the heart of a wide variety of applications ranging from telecommunications and optical gas sensing to biological imaging and metrology. NIR-emitting semiconductor nanowires (NWs), acting both as a miniaturized optical resonator and as a photonic gain medium, are among the best-suited nanomaterials to achieve such goals. In this study, we demonstrate the NIR lasing at 1 mu m from GaAs/GaNAs/GaAs core/shell/cap dilute nitride nanowires with only 2.5% nitrogen. The achieved lasing is characterized by an S-shape pump-power dependence and narrowing of the emission line width. Through examining the lasing performance from a set of different single NWs, a threshold gain, g(th), of 4100-4800 cm(-1), was derived with a spontaneous emission coupling factor, beta, up to 0.8, which demonstrates the great potential of such nanophotonic material. The lasing mode was found to arise from the fundamental HE11a mode of the Fabry-Perot cavity from a single NW, exhibiting optical polarization along the NW axis. Based on temperature dependence of the lasing emission, a high characteristic temperature, T-0, of 160 (+/- 10) K is estimated. Our results, therefore, demonstrate a promising alternative route to achieve room-temperature NIR NW lasers thanks to the excellent alloy tunability and superior optical performance of such dilute nitride materials. Funding Agencies|Swedish Energy Agency [P40119-1]; Swedish Research Council [2015-05532]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; KAKENHI from the Japan Society for the Promotion of Science [16H05970, 23686004]; Kato Foundation for Promotion of Science; Kurata Memorial Hitachi Science and Technology Foundation; Murata Science Foundation

In this chapter, we go over epitaxial growth of bismide thin films, multiple quantum wells, and nanostructures (nanowires) using molecular beam epitaxy (MBE) and their surface morphology, structural, and optical properties are investigated along with device applications. We describe how the Bi content in GaAs1−xBix epilayers grown on (100), (411)A, and (411)B GaAs substrates can be controlled by the growth conditions. Nonstandard growth conditions such as two-substrate-temperature technique (TST) are required for GaAs1−xBix because of the strong tendency of Bi atom segregation under usual growth conditions. We have reported a GaAs0.96Bi0.04/GaAs multiple quantum well LED grown by TST technique with a room temperature photoluminescence and electroluminescence at 1.23 μm emission wavelength. The TST procedure proves as a very efficient method to reduce Bi segregation and thus improves the quality of the GaAsBi layer at GaAs interfaces.

We carry out real-time in situ synchrotron X-ray diffraction on the growth of GaN and AlN on SiC(0001) substrate by molecular beam epitaxy. At the initial growth stage of GaN/SiC or AlN/SiC heterostructure, the epitaxial overlayer develops affected by defects with the strain interaction between SiC, eventually showing characteristic lattice deformations. GaN was almost relaxed at the initial stage, showing the transition of the growth mode from 3D to 2D at around 4 nm. In contrast, AlN coherently grow on SiC(0001) at the initial stage for 13 nm concomitantly showing lattice deformation with the beneath SiC, subsequently showing gradual lattice relaxation.

Nanowires (NWs) with embedded zero-dimensional (0D) quantum dots (QDs) have interesting fundamental properties attractive for a variety of applications. The properties of such embedded QDs can be c ...

We study the effects of annealing on (Ga0.64,In0.36) (N0.045,As0.955) using hard X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements. We observed surface oxidation and termination of the N-As bond defects caused by the annealing process. Specifically, we observed a characteristic chemical shift towards lower binding energies in the photoelectron spectra related to In. This phenomenon appears to be caused by the atomic arrangement, which produces increased In-N bond configurations within the matrix, as indicated by the X-ray absorption fine structure measurements. The reduction in the binding energies of group-III In, which occurs concomitantly with the atomic rearrangements of the matrix, causes the differences in the electronic properties of the system before and after annealing.

This chapter analyses the impacts of alloying with nitrogen on structural properties and recombination processes in GaNAs nanowires (NW). It discusses possible innovative applications of these structures in advanced nano-emitters, where the incorporation of nitrogen induces the formation of self-assembled quantum dot-like states embedded in the NWs. The structural properties of these NWs were investigated by transmission electron microcopy. An important material parameter that affects performance of the NW-based devices is carrier lifetime. The non-radiative lifetime is largely affected by the material quality both in bulk and within near-surface regions. The contribution of the surface-related recombination is known to be especially severe in GaAs-based NW structures due to a large surface-to-volume ratio and the presence of surface states participating in the non-radiative recombination processes. The revealed optical properties of the GaNAs-based NW structures may be attractive for future optoelectronic applications in advanced nano-sized light emitters which could be integrated with silicon technology.

One dimensional electronic materials are expected to be key components owing to their potential applications in nanoscale electronics, optics, energy storage, and biology. Besides, compound semicon ...

We present the growth and strain deformation of sharp-facetted GaAs/GaAsBi core–shell heterostructure nanowires on a Si (111) substrate. The nanowires have a 90 nm wide GaAs core surrounded by an 80 nm thick GaAsBi shell. The sample was analyzed using microbeam synchrotron x-ray diffraction to resolve the local strain status at the GaAs/GaAsBi heterointerface. GaAsBi showed identical lattice constants for its vertical and lateral lattice planes. From the lattice constants, the Bi concentration in GaAsBi was estimated to be approximately 1.3%. In contrast, the GaAs core showed biaxial strain deformation, exhibiting an enlarged vertical lattice constant identical to that of the GaAsBi shell. These layers are coherently grown at the sidewalls of the nanowires, preserving identical vertical lattice constants between the constituent layers in the heterostructure.We present the growth and strain deformation of sharp-facetted GaAs/GaAsBi core–shell heterostructure nanowires on a Si (111) substrate. The nanowires have a 90 nm wide GaAs core surrounded by an 80 nm thick GaAsBi shell. The sample was analyzed using microbeam synchrotron x-ray diffraction to resolve the local strain status at the GaAs/GaAsBi heterointerface. GaAsBi showed identical lattice constants for its vertical and lateral lattice planes. From the lattice constants, the Bi concentration in GaAsBi was estimated to be approximately 1.3%. In contrast, the GaAs core showed biaxial strain deformation, exhibiting an enlarged vertical lattice constant identical to that of the GaAsBi shell. These layers are coherently grown at the sidewalls of the nanowires, preserving identical vertical lattice constants between the constituent layers in the heterostructure.

We report a GaAs0.96Bi0.04/GaAs multiple quantum well (MQW) light emitting diode (LED) grown by molecular beam epitaxy using a two-substrate-temperature (TST) technique. In particular, the QWs and the barriers in the intrinsic region were grown at the different temperatures of [Formula: see text] = 350 °C and [Formula: see text] respectively. Investigations of the microstructure using transmission electron microscopy (TEM) reveal homogeneous MQWs free of extended defects. Furthermore, the local determination of the Bi distribution profile across the MQWs region using TEM techniques confirm the uniform Bi distribution, while revealing a slightly chemically graded GaAs-on-GaAsBi interface due to Bi surface segregation. Despite this small broadening, we found that Bi segregation is significantly reduced (up to 18% reduction) compared to previous reports on Bi segregation in GaAsBi/GaAs MQWs. Hence, the TST procedure proves as a very efficient method to reduce Bi segregation and thus increase the quality of the layers and interfaces. These improvements positively reflect in the optical properties. Room temperature photoluminescence and electroluminescence (EL) at 1.23 μm emission wavelength are successfully demonstrated using TST MQWs containing less Bi content than in previous reports. Finally, LED fabricated using the present TST technique show current-voltage (I-V) curves with a forward voltage of 3.3 V at an injection current of 130 mA under 1.0 kA cm-2 current excitation. These results not only demonstrate that TST technique provides optical device quality GaAsBi/GaAs MQWs but highlight the relevance of TST-based growth techniques on the fabrication of future heterostructure devices based on dilute bismides.

Recent developments in fabrication techniques and extensive investigations of the physical properties of III-V semiconductor nanowires (NWs), such as GaAs NWs, have demonstrated their potential for a multitude of advanced electronic and photonics applications. Alloying of GaAs with nitrogen can further enhance the performance and extend the device functionality via intentional defects and heterostructure engineering in GaNAs and GaAs/GaNAs coaxial NWs. In this work, it is shown that incorporation of nitrogen in GaAs NWs leads to formation of three-dimensional confining potentials caused by short-range fluctuations in the nitrogen composition, which are superimposed on long-range alloy disorder. The resulting localized states exhibit a quantum-dot like electronic structure, forming optically active states in the GaNAs shell. By directly correlating the structural and optical properties of individual NWs, it is also shown that formation of the localized states is efficient in pure zinc-blende wires and is further facilitated by structural polymorphism. The light emission from these localized states is found to be spectrally narrow (similar to 50-130 mu eV) and is highly polarized (up to 100%) with the preferable polarization direction orthogonal to the NW axis, suggesting a preferential orientation of the localization potential. These properties of self-assembled nano-emitters embedded in the GaNAs-based nanowire structures may be attractive for potential optoelectronic applications. Funding agencies: Financial support by the Swedish Energy Agency (grant # P40119-1) and the Swedish Research Council (grants # 2015-05532 and 2008-405) is greatly appreciated. The Knut and Alice Wallenberg Foundation is gratefully acknowledged for support of the Electron Microscopy laboratory in Linkoping.

In this work we investigate properties of ultra-narrow photoluminescence lines originating from recombination of excitons trapped by short-range potential fluctuations, caused by alloy disorder in GaAs/GaNAs core/shell nanowires. From power-dependent photoluminescence measurements we show that the emission behavior is consistent with biexciton-exciton cascade recombination in quantum dots. We also show that the thermal activation energy from the related localized states is of the order of 9–30 meV, suggesting a rather shallow confinement potential.

In this paper we review our recent results on optical properties of coaxial nanowires (NWs) based on dilute nitride alloys, such as GaAsN and GaNP. We show that these structures have a high structural and optical quality, and can potentially be used as polarized nano-scale light sources that emit linearly polarized light with the polarization direction perpendicular to the wire axis even in zinc blende NWs of various diameters. We also demonstrate that, though the GaN x P 1−x alloys have rather wide bandgap energies of 1.9 – 2.3 eV, the coaxial GaNP NWs absorb infrared light via two-step two-photon absorption.

We statistically investigate the development of GaAs/GaAsBi core-multi shell nanowires. The wire diameters were precisely controlled by adjusting the growth procedure. The wire having GaAs/GaAsBi core-shell nanowire, presumably having Bi concentration less than 1%, shows straight sidewall with sphere-shaped structure on the tip. The diameter was 250 nm ± 32 nm. GaAs/GaAs 0.98 Bi 0.02 /GaAs core-multi shell nanowire showed characteristic rough surface. The diameter was 376 nm ± 33 nm. In contrast, when we grew GaAs nanowire with identical growth conditions of the multi shell nanowires, they showed straight sidewall with its diameter described by 375 nm ± 30 nm. The results shows we can control the diameter and the shell structures of the wires. Further, specific surface roughening occurs by the introduction of Bi on the outer shells.

We investigate material conversion of compound semiconductor GaAs nanowires to extend their functions. By heating the GaAs nanowires in Indium melt, the In was introduced into the GaAs nanowire, converting the nanowires to be InGaAs compounds. The further heating treatment in N 2 ambient oxidize the nanowire simultaneously progressing the diffusion of Si element from the substrate, eventually forming the InSiO compound nanowires.

Eleven periods of highly strained GaAsBi/GaAs MQWs were grown on GaAs (100) substrates by MBE to study Bi incorporation dependent on As 4 flux. We obtained largest Bi incorporation at As 4 BEP of 1.0 × 10−5 mbar. From analysis of incorporated Bi by HRXRD, the growth mode transfer is suggested at smaller or larger regime of an As 4 BEP of 1.0 × 10−5 mbar. In the smaller regime, the Bi incorporation was enhanced with increase of As BEP. On other hand, Bi incorporation was almost constant at the higher regime. The AFM image shows that the sample grown at As 4 BEP of 1.0 × 10−5 mbar has a smooth surface region and island like region, overall rms roughness is 6.8 nm. The PL obtained at 10 K showed a clear redshift of peak positions reflecting incorporation of Bi. At largest Bi concentration of 3.8%, we observe a peak emitting over 1100 nm at 10K for MQWs.

GaInNAs was proposed and created in 1995. It can be grown pseudomorphically on a GaAs substrate and is a light-emitting material with a bandgap energy that corresponds to near infrared. By combining GaInNAs with GaAs, an ideal band lineup for laser-diode application is achieved. This paper presents the reproducible growth of high-quality GaInNAs by molecular beam epitaxy. Examining the effect of nitrogen introduction and its correlation with impurity incorporation, we find that Al is unintentionally incorporated into the epitaxial layer even though the Al cell shutter is closed, followed by the concomitant incorporation of O and C. A gas-phase-scattering model can explain this phenomenon, suggesting that a large amount of N2 gas causes the scattering of residual Al atoms with occasional collisions resulting in the atoms being directed toward the substrate. Hence, the reduction of the sublimated Al beam during the growth period can suppress the incorporation of unintentional impurities, resulting in a highly pure epitaxial layer.

We investigate the band gap engineering with sub-monolayer nitrogen introduction (: N δ-doping) at the middle of InGaAs/GaAs quantum well. Using plasma-assisted molecular beam epitaxy, we prepare samples varying the introduced nitrogen between 0 and 0.4 monolayer. The growths are carried out at substrate temperature of 520 C, comparatively higher than conventional substrate temperature for dilute nitride compounds. This induces the roughening of the growth front, slightly enhancing the nitrogen incorporation within the crystal. The as-grown and annealed samples show clear room temperature photoluminescence, indicating the band gap shrinkage depending on the amount of nitrogen.