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Recent work showing a strong quality improvement of the Si/SiO2 material system by low temperature atomic hydrogen annealing (AHA), and the fact that III–V semiconductors outperform Si in many applications makes the investigation of AHA on III–V/high-k interfaces to a very interesting topic. In this work, the potential of AHA as a low temperature annealing treatment of InGaAs metal–oxide–semiconductor field-effect transistors is presented and compared to conventional annealing in a rapid thermal process (RTP) system using forming gas. It is found that post metal annealing in atomic hydrogen greatly enhances the quality of the metal–oxide–semiconductor structure in terms of effective mobility, minimum subthreshold swing, and reliability. The device performance is comparable to RTP annealing but can be performed at a lower temperature, which opens up for integration of more temperature-sensitive materials in the device stack. [ABSTRACT FROM AUTHOR]

Aerotaxy, a recently invented aerosol-based growth method for nanostructures, has been shown to hold great promise in making III-V nanowires more accessible for cheap mass-production. Aerotaxy nanowire surface structure and chemistry, however, remains unexplored, which is unfortunate since this can influence (opto)electronic properties. We investigate the surfaces of aerotaxy grown GaAs nanowires using synchrotron based high resolution X-ray photoelectron spectroscopy and high resolution atomic force microscopy. We observe that increasing the concentration of the p-type dopant diethylzinc to very high levels during nanowire growth significantly changes the surface morphology and leads to a strong suppression of native surface oxide formation. Our findings indicate that up to 1.8 monolayers of Zn are present on the nanowire surface after growth. Finally, we find that this also influences the Fermi level pinning of the surface. We suggest that Zn present on the surface after growth could play a role in the strongly hindered oxidation of the III-V compound when exposed to air. The aerotaxy nanowires generally exhibit a round cross section, while a significant smoothening of the surface morphology along the nanowire appears for very high nominal doping levels likely as a result of slight reshaping during growth in the presence of Zn. Given that surface oxide and a rough morphology can be detrimental to nanowire electrical and optical performance, the ability to reduce them as a side effect of dopant introduction will benefit future applications. Finally, the observed hindering of oxidation during air transport can allow for reliable post-growth processing in separate systems. [ABSTRACT FROM AUTHOR]

Self-assembled, atomic diffusion controlled growth of InN quantum dots was realized on the side facets of dislocation-free and c-oriented GaN nanowires having a hexagonal cross-section. The nanowires were synthesized by selective area metal organic vapor phase epitaxy. A 3 Å thick InN wetting layer was observed after growth, on top of which the InN quantum dots formed, indicating self-assembly in the Stranski-Krastanow growth mode. We found that the InN quantum dots can be tuned to nucleate either preferentially at the edges between GaN nanowire side facets, or directly on the side facets by tuning the adatom migration by controlling the precursor supersaturation and growth temperature. Structural characterization by transmission electron microscopy and reciprocal space mapping show that the InN quantum dots are close to be fully relaxed (residual strain below 1%) and that the c-planes of the InN quantum dots are tilted with respect to the GaN core. The strain relaxes mainly by the formation of misfit dislocations, observed with a periodicity of 3.2 nm at the InN and GaN hetero-interface. The misfit dislocations introduce I1 type stacking faults (…ABABCBC…) in the InN quantum dots. Photoluminescence investigations of the InN quantum dots show that the emissions shift to higher energy with reduced quantum dot size, which we attribute to increased quantum confinement. [ABSTRACT FROM AUTHOR]

Folding two-dimensional graphene around one-dimensional III–V nanowires yields a new class of hybrid nanomaterials combining their excellent complementary properties. However, important for high-quality electrical and optical performance, needed in many applications, are well-controlled oxide-free interfaces and a tight folding morphology. To improve the interface chemistry between the graphene and InAs, we annealed the samples in atomic hydrogen. Using surface-sensitive imaging, we found that the III–V native oxides in the interface can be reduced at temperatures that maintain the graphene and the III–V nanostructures. Transferring both single- and multilayer graphene flakes onto InAs NWs, we found that single layers fold tightly around the NWs, while the multilayers fold weakly with a decline of only a few degrees. Annealing in atomic hydrogen further tightens the folding. Together, this indicates that high-quality morphological and chemical control of this hybrid material system is possible, opening for future devices for quantum technologies and optoelectronics. [ABSTRACT FROM AUTHOR]

Ferroelectric HfxZr1–xO2 (HZO) is typically achieved by crystallization of an amorphous thin film via rapid thermal processing (RTP) at time scales of seconds to minutes. For integration on III–V semiconductors, this approach can severely degrade the sensitive HZO/III–V interface. To evaluate whether a reduced thermal budget can improve the interface quality, millisecond duration thermal anneals are utilized using a flash lamp annealer (FLA) on HZO/InAs capacitors. Through thorough electrical characterization such as polarization hysteresis, endurance, and capacitance‐voltage measurements, as well as synchrotron‐based chemical interface characterization, the FLA and RTP treatments are compared and the FLA results are found in lower interface defect density and higher endurance, but also have generally lower remanent polarization (Pr) compared to RTP. Additionally, ways to achieve high Pr and low interface defect density using multiple lower energy flashes, as well as by pre‐crystallization during the ALD growth step are investigated. Using FLA, Pr exceeding 20 µC cm−2 is achieved, with extended endurance properties compared to RTP treatment and a considerably decreased defect density, indicative of a higher quality HZO/InAs interface. This work presents valuable insight into the successful integration of ferroelectric HZO on low thermal budget III–V semiconductors. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) is one of the backbones for today's electronic device fabrication. A critical property of ALD is the layer-by-layer growth, which gives rise to the atomic-scale accuracy. However, the growth rate – or growth per cycle – can differ significantly depending on the type of system, molecules used, and several other experimental parameters. Typically, ALD growth rates are constant in subsequent ALD cycles, making ALD an outstanding deposition technique. However, contrary to this steady-state – when the ALD process can be entirely decoupled from the substrate on which the material is grown – the deposition's early stage does not appear to follow the same kinetics, chemistry, and growth rate. Instead, it is to a large extent determined by the surface composition of the substrate. Here, we present evidence of oxygen relocation from the substrate-based oxide, either the thermal or native oxide of InAs, to the overlayer of HfO2 in the initial ALD phase. This phenomenon enables control of the thickness of the initial ALD layer by controlling the surface conditions of the substrate prior to ALD. On the other hand, we observe a complete removal of the native oxide from InAs already during the first ALD half-cycle, even if the thickness of the oxide layer exceeds one monolayer, together with a self-limiting thickness of the ALD layer of a maximum of one monolayer of HfO2. These observations not only highlight several limitations of the widely used ligand exchange model, but they also give promise for a better control of the industrially important self-cleaning effect of III–V semiconductors, which is crucial for future generation high-speed MOS. [ABSTRACT FROM AUTHOR]

The impact of electrical current on the structure of single free‐standing Be‐doped GaAs nanowires grown on a Si 111 substrate is investigated. Single nanowires have been structurally analyzed by X‐ray nanodiffraction using synchrotron radiation before and after the application of an electrical current. The conductivity measurements on single nanowires in their as‐grown geometry have been realized via W‐probes installed inside a dual‐beam focused ion beam/scanning electron microscopy chamber. Comparing reciprocal space maps of the 111 Bragg reflection, extracted perpendicular to the nanowire growth axis before and after the conductivity measurement, the structural impact of the electrical current is evidenced, including deformation of the hexagonal nanowire cross section, tilting, and bending with respect to the substrate normal. For electrical current densities below 30 A mm−2, the induced changes in the reciprocal space maps are negligible. However, for a current density of 347 A mm−2, the diffraction pattern is completely distorted. The mean cross section of the illuminated nanowire volume is reconstructed from the reciprocal space maps before and after the application of electrical current. Interestingly, the elongation of two pairs of opposing side facets accompanied by shrinkage of the third pair of facets is found. The variations in the nanowire diameter, as well as their tilt and bending, are confirmed by scanning electron microscopy. To explain these findings, material melting due to Joule heating during voltage/current application accompanied by anisotropic deformations induced by the W‐probe is suggested. [ABSTRACT FROM AUTHOR]

Laterally grown InxGa1−xAs nanowires (NWs) are promising candidates for radio frequency and quantum computing applications, which, however, can require atomic scale surface and interface control. This is challenging to obtain, not least due to ambient air exposure between fabrication steps, which induces surface oxidation. The geometric and electronic surface structures of InxGa1−xAs NWs and contacts, which were grown directly in a planar configuration, exposed to air, and then subsequently cleaned using atomic hydrogen, are studied using low-temperature scanning tunneling microscopy and spectroscopy (STM/S). Atomically flat facets with a root mean square roughness of 0.12 nm and the InGaAs (001) 4 × 2 surface reconstruction are observed on the top facet of the NWs and the contacts. STS shows a surface bandgap variation of 30 meV from the middle to the end of the NWs, which is attributed to a compositional variation of the In/Ga element concentration. The well-defined facets and small bandgap variations found after area selective growth and atomic hydrogen cleaning are a good starting point for achieving high-quality interfaces during further processing. [ABSTRACT FROM AUTHOR]

Defects at the interface between InAs and a native or high permittivity oxide layer are one of the main challenges for realizing III-V semiconductor based metal oxide semiconductor structures with superior device performance. Here we passivate the InAs(100) substrate by removing the native oxide via annealing in ultra-high vacuum (UHV) under a flux of atomic hydrogen and growing a stoichiometry controlled oxide (thermal oxide) in UHV, prior to atomic layer deposition (ALD) of an Al2O3 high-k layer. The semiconductor-oxide interfacial stoichiometry and surface morphology are investigated by synchrotron based X-ray photoemission spectroscopy, scanning tunneling microscopy, and low energy electron diffraction. After thermal oxide growth, we find a thin non-crystalline layer with a flat surface structure. Importantly, the InAs-oxide interface shows a significantly decreased amount of In3+, As5+, and As0 components, which can be correlated to electrically detrimental defects. Capacitance-voltage measurements confirm a decrease of the interface trap density in gate stacks including the thermal oxide as compared to reference samples. This makes the concept of a thermal oxide layer prior to ALD promising for improving device performance if this thermal oxide layer can be stabilized upon exposure to ambient air. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor–oxide interface. Here, we directly observe the chemical reactions at the surface during the first cycle of hafnium dioxide deposition on indium arsenide under realistic synthesis conditions using photoelectron spectroscopy. We find that the widely used ligand exchange model of the ALD process for the removal of native oxide on the semiconductor and the simultaneous formation of the first hafnium dioxide layer must be significantly revised. Our study provides substantial evidence that the efficiency of the self-cleaning process and the quality of the resulting semiconductor–oxide interface can be controlled by the molecular adsorption process of the ALD precursors, rather than the subsequent oxide formation. [ABSTRACT FROM AUTHOR]

Utilizing semiconductor nanowiresfor (opto)electronics requiresexact knowledge of their current–voltage properties. We reportaccurate on-top imaging and I–V characterizationof individual as-grown nanowires, using a subnanometer resolutionscanning tunneling microscope with no need for additional microscopytools, thus allowing versatile application. We form Ohmic contactsto InP and InAs nanowires without any sample processing, followedby quantitative measurements of diameter dependent I–Vproperties with a very small spread in measured values comparedto standard techniques. [ABSTRACT FROM AUTHOR]

The growth and atomic/electronic structure of molecular beam epitaxy-grown ErAs nanoparticles and nanorods embedded within a GaAs matrix are examined for the first time via cross-sectional scanning tunneling microscopy and spectroscopy. Cross sections enable the interrogation of the internal structure and are well suited for studying embedded nanostructures. The early stages of embedded ErAs nanostructure growth are examined via these techniques and compared with previous cross-sectional transmission electron microscopy work. Tunneling spectroscopy I(V) for both ErAs nanoparticles and nanorods was also performed, demonstrating that both nanostructures are semimetallic [ABSTRACT FROM AUTHOR]

The Half Heuslers are currently an attractive family of compounds for high temperature thermoelectrics research, and recently, there has been renewed interest since some of these compounds are proposed to be topological insulators. NiTiSn belongs to the family of 18 valence electron Half Heuslers that are predicted to be semiconducting, despite being composed entirely of metallic elements. The growth of the Half Heusler compound NiTiSn by molecular beam epitaxy is demonstrated. The NiTiSn films are epitaxial and single crystalline as observed by reflection high-energy electron diffraction and x-ray diffraction. Temperature dependent transport measurements suggest the films may be semiconducting, but with a high background carrier density indicative of a high density of electrically active defect states. Methods of protecting the sample surface for synchrotron-based photoemission measurements are explored. These methods may be applied to the study of surface electronic structure in unconventional materials. [ABSTRACT FROM AUTHOR]

The article cites a research study that determines the atomic and electronic structures for several surface reconstructions of the half-Heusler CoTiSb surface, a building block for all-Heusler-based spintronic and topological heterostructures. The researchers aimed to predict the surface structure and properties of these novel quantum materials.

Metal-halide perovskites (MHPs) have gained substantial interest in the energy and optoelectronics field. MHPs in nanostructure forms, such as nanocrystals and nanowires (NWs), have further expanded the horizons for perovskite nanodevices in geometry and properties. A partial anion exchange within the nanostructure, creating axial heterojunctions, has significantly augmented the potential applications. However, surface degradation and halide ion migration are deteriorating device performance. Quantitative analysis of halide metal concentration and mapping of the electrical surface potential along the operating NW device are needed to better understand ion transportation, band structure, and chemical states, which have not been experimentally reported yet. This requires a characterization approach that is capable to provide surface-sensitive chemical and electrical information at the subμm scale. Here, we used operando nanofocused X-ray photoelectron spectroscopy (nano-XPS) to study CsPbBr 3 /CsPb(Br 1- x Cl x ) 3 heterojunction NW devices with a spatial resolution of 120 nm. We monitored Br - and Cl - ion migration and comprehended the potential drop along the device during operation. Ion migration and healing of defects and vacancies are found for applied voltages of as low as 1 V. We present a model delineating band bending along the device based on precise XPS peak positions. Notably, a reversible redox reaction of Pb was observed, that reveals the interaction of migrating halide ions, vacancies, and biased metal electrodes under electrical operation. We further demonstrate how X-ray-induced surface modification can be avoided, by limiting exposure times to less than 100 ms. The results facilitate the understanding of halide ion migration in MHP nanodevices under operation.

Nonvolatile memory devices based on ferroelectric Hf x Zr 1- x O 2 (HZO) show great promise for back-end integrable storage and for neuromorphic accelerators, but their adoption is held back by the inability to scale down the HZO thickness without violating the strict thermal restrictions of the Si CMOS back end of line. In this work, we overcome this challenge and demonstrate the use of nanosecond pulsed laser annealing (NLA) to locally crystallize areas of an ultrathin (3.6 nm) HZO film into the ferroelectric orthorhombic phase. Meanwhile, the heat induced by the pulsed laser is confined to the layers above the Si, allowing for back-end compatible integration. We use a combination of electrical characterization, nanofocused scanning X-ray diffraction (nano-XRD), and synchrotron X-ray photoelectron spectroscopy (SXPS) to gain a comprehensive view of the change in material and interface properties by systematically varying both laser energy and the number of laser pulses on the same sample. We find that NLA can provide remanent polarization up to 2 P r = 11.6 μC/cm 2 in 3.6 nm HZO, albeit with a significant wake-up effect. The improved TiN/HZO interface observed by XPS explains why device endurance goes beyond 10 7 cycles, whereas an identical film processed by rapid thermal processing (RTP) breaks already after 10 6 cycles. All in all, NLA provides a promising approach to scale down the ferroelectric oxide thickness for emerging HZO ferroelectric devices, which is key for their integration in scaled process nodes.

The surface chemistry of the initial growth during the first or first few precursor cycles in atomic layer deposition is decisive for how the growth proceeds later on and thus for the quality of the thin films grown. Yet, although general schemes of the surface chemistry of atomic layer deposition have been developed for many processes and precursors, in many cases, knowledge of this surface chemistry remains far from complete. For the particular case of HfO 2 atomic layer deposition on a SiO 2 surface from an alkylamido-hafnium precursor and water, we address this lack by carrying out an operando atomic layer deposition experiment during the first cycle of atomic layer deposition. Ambient-pressure X-ray photoelectron spectroscopy and density functional theory together show that the decomposition of the metal precursor on the stoichiometric SiO 2 surface in the first half-cycle of atomic layer deposition proceeds via a bimolecular reaction mechanism. The reaction leads to the formation of Hf-bonded methyl methylene imine and free dimethylamine. In addition, ligand exchange takes place involving the surface hydroxyls adsorbed at defect sites of the SiO 2 surface., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Mismatch between adjacent atomic layers in low-dimensional materials, generating moiré patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear as ideal candidates for the study of these phenomena due to the weak coupling between layers. Here we discover and investigate the origin of 1D moiré stripes on the surface of Bi 2 Se 3 TI thin films and nanobelts. Scanning tunneling microscopy and high-resolution transmission electron microscopy reveal a unidirectional strained top layer, in the range 14-25%, with respect to the relaxed bulk structure, which cannot be ascribed to the mismatch with the substrate lattice but rather to strain induced by a specific growth mechanism. The 1D stripes are characterized by a spatial modulation of the local density of states, which is strongly enhanced compared to the bulk system. Density functional theory calculations confirm the experimental findings, showing that the TI surface Dirac cone is preserved in the 1D moiré stripes, as expected from the topology, though with a heavily renormalized Fermi velocity that also changes between the top and valley of the stripes. The strongly enhanced density of surface states in the TI 1D moiré superstructure can be instrumental in promoting strong correlations in the topological surface states, which can be responsible for surface magnetism and topological superconductivity.

Atomic layer deposition (ALD) is one of the backbones for today's electronic device fabrication. A critical property of ALD is the layer-by-layer growth, which gives rise to the atomic-scale accuracy. However, the growth rate - or growth per cycle - can differ significantly depending on the type of system, molecules used, and several other experimental parameters. Typically, ALD growth rates are constant in subsequent ALD cycles, making ALD an outstanding deposition technique. However, contrary to this steady-state - when the ALD process can be entirely decoupled from the substrate on which the material is grown - the deposition's early stage does not appear to follow the same kinetics, chemistry, and growth rate. Instead, it is to a large extent determined by the surface composition of the substrate. Here, we present evidence of oxygen relocation from the substrate-based oxide, either the thermal or native oxide of InAs, to the overlayer of HfO 2 in the initial ALD phase. This phenomenon enables control of the thickness of the initial ALD layer by controlling the surface conditions of the substrate prior to ALD. On the other hand, we observe a complete removal of the native oxide from InAs already during the first ALD half-cycle, even if the thickness of the oxide layer exceeds one monolayer, together with a self-limiting thickness of the ALD layer of a maximum of one monolayer of HfO 2 . These observations not only highlight several limitations of the widely used ligand exchange model, but they also give promise for a better control of the industrially important self-cleaning effect of III-V semiconductors, which is crucial for future generation high-speed MOS.