GaAs Interface Research Articles

Rapid oxidation of semiconductors at room temperature with a basic plasma cleaner

This paper shows how a simple modification of the electrodes in a basic commercial plasma cleaner allowed the oxidation of compound semiconductors (GaAs) and Si at room temperature. We explained the oxidation of the semiconductor surface by the participation of aluminum atoms evaporated from the electrode surface in the discharge, which resulting in additional ultraviolet (UV) radiation from the plasma. The UV radiation not only increases the decomposition of oxygen molecules adsorbed on the surface but also results in photoionization of GaAs with the formation of Ga and As ions at the oxide–GaAs interface. In addition to obtaining oxides on semiconductor surfaces, the modified device proved to be an effective tool for etching amorphous carbon films.

Investigation of the CdZnTe (2 1 1) and (1 3 3) films grown on GaAs (2 1 1) controlled by temperature: Experiment and first-principles calculations

The origin and evolution of dual epitaxy in CdZnTe epilayer grown on GaAs substrates by close spaced sublimation has been studied, both (211) and (133) films are suitable for HgCdTe growth. And the effect of growth temperature on the orientation and crystalline quality of CdZnTe films has been investigated, more uniform orientation of adjoining growth islands in the growth of (133) film leads to a smoother surface with less threading dislocations and roughness. The interfacial properties of CdZnTe films were studied by the first-principles calculations combined with scanning transmission electron microscopy observations. By calculation the work of adhesion between the CdTe films and GaAs (211), obtain the CdTe (211)/GaAs (211) interface is the more stable interface structure at the initial nucleation stage. Combining to the results of experiment, at higher growth temperature, only (133) nucleus can reach the critical size and thus stabilize the growth. More importantly, the results on the dual epitaxy of CdZnTe films are expected to play a crucial role in guiding the dual epitaxy growth of other zincblende-type crystal.

Extended defects in GaAs/GaAs1-xSbx/GaAs (001) heterostructures

The atomic-scale structure of extended defects in GaAs/GaAs1-xSbx/GaAs (001) heterostructures has been characterized using aberration-corrected scanning transmission electron microscopy. The defect located at the tensile-strained GaAs(cap)/GaAs0.34Sb0.66 interface had no edge component in the {11¯0} projection plane and is identified as either a dissociated screw dislocation or a partial dislocation dipole. The associated intrinsic stacking fault is bounded by two 30° Shockley partial dislocations of opposite sign. Another defect, located at the compressively-strained GaAs0.91Sb0.09/GaAs(substrate) interface, is identified as a dissociated 90° dislocation. The associated intrinsic stacking fault is bounded by a 30° Shockley partial dislocation and a partial dislocation with a Burgers vector of either a/6[411¯] or a/6[141¯], where a is the lattice constant. Unpaired atomic columns observed at the cores of the 30° Shockley partial dislocations indicate that both defects belong primarily to the glide set.

Strong coupling between a topological insulator and a III-V heterostructure at terahertz frequency

We theoretically probe the emergence of strong coupling in a system consisting of a topological insulator (TI) and a III-V heterostructure using a numerical approach based on the scattering matrix formalism. Specifically, we investigate the interactions between terahertz excitations in a structure composed of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ and GaAs materials. We find that the interaction between the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ layer and AlGaAs/GaAs quantum wells with intersubband transitions (ISBTs) in the terahertz frequency regime creates new hybrid modes, namely Dirac plasmon-phonon-ISBT polaritons. The formation of these hybrid modes results in anticrossings (spectral mode splitting) whose magnitude is an indication of the strength of the coupling. By varying the structural parameters of the constituent materials, our numerical calculations reveal that the magnitude of splitting depends strongly on the doping level and the scattering rate in the AlGaAs/GaAs quantum wells, as well as on the thickness of the GaAs spacer layer that separates the quantum-well structure from the TI layer. Our results reveal the material and device parameters required to obtain experimentally observable signatures of strong coupling. Our model includes the contribution of an extra two-dimensional hole gas (2DHG) that is predicted to arise at the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$/GaAs interface, based on density functional theory (DFT) calculations that explicitly account for details of the atomic terminations at the interface. The presence of this massive 2DHG at the TI/III-V interface shifts the dispersion of the Dirac plasmon-ISBT polaritons to higher frequencies. The damping rate at this interface, in contrast, compensates the effect of the 2DHG. Finally, we observe that the phonon resonances in the TI layer are crucial to the coupling between the THz excitations in the TI and III-V materials.

Atomically sharp, crystal phase defined GaAs quantum dots

Crystal phase defined heterostructures, or polytype heterostructures, are atomically sharp with no intermixing, which makes them ideal contenders for a wide range of applications. Although polytype quantum dots have shown promising results as single photon sources, a high degree of control on the dimensions and the number of polytype quantum dots is necessary before any application can be developed. In this work, we show results from optical characterization of highly controlled wurtzite (wz)–zinc blende (zb) GaAs quantum dots with sharp photoluminescence signal and a strong indication of 0D density of states. One band effective mass calculations show good agreement with the measured data. Radially confined nanowires with a single wz–zb GaAs interface also show sharp photoluminescence signal and 0D density of states. This indicates the existence of quantum dot like states in triangular wells formed at the wz–zb GaAs interface. These results show the potential of polytype quantum dots for physics and optics applications.

Influence of Finishing the Surface of GaAs on the Properties of Au–GaAs Interfaces

Influence of Finishing the Surface of GaAs on the Properties of Au–GaAs Interfaces

Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination

Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide–GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces.

Polymer Brush-GaAs Interface and Its Use as an Antibody-Compatible Platform for Biosensing.

Despite evidence showing that polymer brushes (PBs) are a powerful tool used in biosensing for minimizing nonspecific interactions, allowing for optimization of biosensing performance, and the fact that GaAs semiconductors have proven to have a remarkable potential for sensitive biomolecule detection, the combination of these two robust components has never been considered nor evaluated as a platform for biosensing applications. This work reports different methodologies to prepare and tune PBs on the GaAs interface (PB–GaAs) and their potential as useful platforms for antibody grafting, with the ultimate goal of demonstrating the innovative and attractive character of the PB–GaAs interfaces in the enhanced capture of antibodies and control of nonspecific interactions. Three different functionalization approaches were explored, one “grafting-to” and two “grafting-from,” in which atom transfer radical polymerization (ATRP) was performed, followed by their corresponding characterizations. Demonstration of the compatibility of Escherichia coli (E. coli) and Legionella pneumophila (Lp) antibodies with the PB–GaAs platform compared to the results obtained with conventional biosensing architectures developed for GaAs indicates the attractive potential for operation of a sensitive biosensor. Furthermore, these results showed that by carefully choosing the nature and preparation methodology of a PB–GaAs interface, it is possible to effectively tune the affinity of PB–GaAs-based sensors toward E. coli and Lp antibodies ultimately demonstrating the superior specificity of the developed biosensing platform.

The influence of growth interruption on the luminescence properties of Ga(As,Sb)-based type II heterostructures

The influence of growth interruption on the luminescence properties of the Ga(As,Sb)/GaAs interface have been studied by continous wave and time resolved photoluminescence spectrosocopy in type II Ga(As,Sb)/GaAs/(Ga,In)As double quantum well structures. A specific highly selective etching technique in combination with atomic force microscopy (AFM) is used to analyze the morphology of the Ga(As,Sb) interface layers. The type II charge transfer recombination has been used as sensitive probe. It was found, that highest luminescence quantum efficiency can be achieved using a 10s growth interruption applying a stabilization using both precursor sources for the anion sublattice.

Direct Bonding of GaAs and Diamond for High Power Device Applications

Direct bonding of GaAs and diamond was successfully achieved by surface activated bonding (SAB) method at room temperature. The structures of GaAs/diamond interface before and after annealing at 400 ℃ were investigated by transmission electron microscope (TEM). A 3-nm-thick crystal defect layer was formed at the bonding interface, the change in the crystal defect layer thickness was not observed after annealing. There were no nanovoids and micro-cracks observed at the interface with annealing at temperature 400 ℃. These results indicated that the GaAs/diamond interface has high thermal stability and can withstand the temperature rise of power devices during operating.GaAs-based power devices have excellent electron transport properties and make it suitable for high frequency operation at high frequency. The output power and the lifetime of GaAs devices are largely degraded by the temperature rise of the active region during operating. The thermal conductivity of GaAs is very small, so that the generated heat by self-heating cannot be sufficiently dissipated through the substrate. Diamond has the highest thermal conductivity among materials and is an ideal material to suppress the temperature rise of the devices. The integration of the GaAs-based devices and diamond will be a more promising approach for improving the heat dissipation ability of the devices. However, since there is a large mismatch between the thermal expansion coefficients and lattice constants of GaAs and diamond, the direct growth of GaAs on diamond is quite difficult and vice versa. We have achieved the direct bonding of diamond and Si at room temperature using surface activated bonding (SAB) method and obtained the excellent thermal stability bonding interface.1-3 In this study, we examine the structures of the diamond/GaAs bonding interface and effects of thermal annealing on the interfacial structure of the interface by transmission electron microscopy (TEM).GaAs epitaxial layer grown on GaAs substrate was bonded to diamond by SAB method at room temperature. GaAs epitaxial substrate was composed of a 200 nm thick GaAs and a 100 nm thick InGaP layers grown on GaAs. After bonding, the GaAs substrate and InGaP layer were removed by mechanical polishing and selective wet etching to obtain 200 nm thick GaAs layer bonded to diamond substrates. The structures of the GaAs/diamond bonding interface were investigated by TEM observation. The TEM samples were fabricated by using a focused ion beam (FIB) technique.The cross-sectional TEM images of the GaAs/diamond bonding interface without and with annealing at 400°C for 5 min are shown in Fig 1(a) and 1(b), respectively. A crystal defect layer with a thickness of about 3 nm was observed in the as-bonded interface. The thickness of the crystal defect layer did not change, but no voids or cracks were observed at the bonding interface after annealing. These results indicate that the bonding interface of diamond and GaAs has an excellent thermal stability, which is extremely qualified for the heat dissipation of the devices.Acknowledgements This work was partly supported by Hirose International Scholarship Foundation. The fabrication of the TEM samples and part of the TEM observations were respectively performed at The Oarai Center and at the Laboratory of Alpha-Ray Emitters in IMR under the Inter-University Cooperative Research in IMR of Tohoku University (NO. 18M0045 and 19M0037).References Liang, S. Masuya, M. Kasu, N. Shigekawa, Appl. Phys. Lett. 2017, 110, No.111603.Liang, S. Masuya, S. Kim, T. Oishi, M. Kasu, N. Shigekawa, Appl. Phys. Express 2019, 12, No. 016501.Liang, Y. Zhou, S. Masuya, F. Gucmann, M. Singh, J. Pomeroy, S. Kim, M. Kuball, M. Kasu, N. Shigekawa, Diam. Relat. Mater. 2019, 93, 187 – 192. Figure 1

Graphene transfer passivates GaAs

Graphene–semiconductor junction interface states influence the carrier recombination processes in emerging optoelectronic devices. The large density of interface states in the graphene–GaAs junction is partly formed by oxidation in air of the GaAs surface. A graphene transfer presented herein reduces the arsenic species in the GaAs oxide and maintains the reduction over a span of at least one year. The photoluminescence and terahertz emission spectra show reduced surface trapping of photogenerated carriers in GaAs with graphene-capped oxide. These findings demonstrate a 2D material transfer that passivates a 3D semiconductor surface. A consequence of the passivation is observed by photoreflectance modulation spectroscopy of graphene covered semi-insulating GaAs. The built-in surface field is sufficiently screened by optically pumped carriers to reveal an enhanced excitonic absorption just below the GaAs bandgap. The absorption critical point anomalously red shifts by 4–6 meV from the bulk exciton characteristic energy, an effect we attribute to the exciton absorption occurring closer to the graphene–GaAs interface and influenced by the near-surface GaAs dielectric polarization.

The origin of constant phase element in equivalent circuit of MIS (n) GaAs structures

The Au/Pd/Ti–SiO2-(n) GaAs properties have been analyzed via impedance spectroscopy (IS), as well as DLTS and ICTS, to identify the origin of electron processes responsible for existence of constant phase elements (CPE) in an equivalent circuits of that structure. We showed that CPEs connected in series with resistance represents the electron processes associated with deep levels in GaAs and/or interface states at SiO2-(n) GaAs interface, depending on the value of n of CPE parameter. CPE with n close to 1 characterize the electron processes associated with EL2 deep level, and CPE with n = 0.5–0.65 the complex electron processes associated with EL3 deep level and interface states together. We stated that constant phase elements in equivalent circuits of MIS-GaAs structures with large frequency dispersion of electrical characteristics can be the result of more than one electron process.

Numerical Study of Carrier Transport in n+/n/n+GaAs/AlGaAs Heterostructure at High Current Densities

Carrier transport across isotype GaAs/Al0.4Ga0.6As graded heterojunction has been numerically studied at high injection levels in the framework of the energy balance model. It is shown that, under reverse bias, impact ionization in the domain formed at the heterojunction leads to accumulation of electron-hole plasma in GaAs, but does not cause a breakdown. The latter occurs when the domain reaches the N/N+ interface in AlGaAs and impact ionization is developed throughout the AlGaAs layer. By contrast, under forwarding bias, the initial domain at the heterojunction rapidly disappears with increasing voltage, and in its place, a peak of an electric field of the opposite sign arises since the carrier mobilities of GaAs and AlGaAs are different. Impact ionization in the peak gives rise to a new domain at the n+/n interface in GaAs, which leads to breakdown and the appearance of negative differential resistance. It is shown that a peak of electron temperature is formed near the heterojunction for both current directions. However, the reasons why it appears are different. Under reverse bias, the electrons are heated by the electric field in the domain, while under forwarding bias, it is caused by the energy gradient of the conduction-band edge in the graded-composition layer of the heterojunction. The surprising thing is that, under reverse bias, electrons in GaAs remain cold throughout the whole region extending to the junction at all currents, which results in the extremely great and physically unreasonable values of the velocity overshoot.

Probing Electronic Strain Generation by Separated Electron-Hole Pairs Using Time-Resolved X-ray Scattering

Photogeneration of excess charge carriers in semiconductors produces electronic strain. Under transient conditions, electron-hole pairs may be separated across a potential barrier. Using time-resolved X-ray diffraction measurements across an intrinsic AlGaAs/n-doped GaAs interface, we find that the electronic strain is only produced by holes, and that electrons are not directly observable by strain measurements. The presence of photoinduced charge carriers in the n-doped GaAs is indirectly confirmed by delayed heat generation via recombination.

Spin generation in completely MBE-grown Co2FeSi/MgO/GaAs lateral spin valves

We demonstrate first measurements of successful spin generation in crystalline ${\mathrm{Co}}_{2}\mathrm{FeSi}$/MgO/GaAs hybrid structures grown by molecular-beam epitaxy (MBE) with different MgO interlayer thicknesses. Using nonlocal spin valve and nonlocal Hanle measurement configurations, we determine spin lifetimes of $\ensuremath{\tau}\ensuremath{\approx}100$ ns and spin diffusion lengths of $\ensuremath{\lambda}\ensuremath{\approx}5.6\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$ for different MgO layer thicknesses, proving the high quality of the GaAs transport channel. For an optimized MgO layer thickness, the bias dependence of the spin valve signals indicates the verification of the half-metallic gap (upper edge) of ${\mathrm{Co}}_{2}\mathrm{FeSi}$ in accordance with first-principles calculations. In addition to that, spin generation efficiencies of up to $18%$ reveal the high potential of MgO interlayers at the ${\mathrm{Co}}_{2}\mathrm{FeSi}$/GaAs interface for further device applications.

Engineering Ultrafast Carrier Dynamics at the Graphene/GaAs Interface by Bulk Doping Level

AbstractCarrier dynamics, the most fundamental process in electronics and optoelectronics, has drawn great attentions owing to its crucial role in property engineering of materials. Exploration and regulation of carrier dynamics are essential for designing devices with specific functions and optimizing their performances. However, the lack of conventional tools with simultaneous ultrafast temporal and ultrasmall spatial resolution has impeded direct observation and manipulation of carrier dynamics at both the femtosecond and nanometer scale. In this study, the direct observation and modulation of ultrafast carrier dynamics at the graphene/gallium arsenide (GaAs) interface is achieved by tuning the doping level of bulk GaAs. This successful characterization is performed using advanced in situ photoemission electron microscopy combined with the ultrafast pump–probe technique. It is found that a change in the doping level in GaAs can change its band bending and switch the hot‐carrier transfer direction at the graphene/GaAs interface with a lifetime reduction of nearly six times. This work paves the way of engineering ultrafast carrier dynamics at 2D interfaces by modifying the 3D bulk properties, and also provides a platform for fundamental studies of ultrafast physics with high spatial resolution.

Segregation of point defects at the CuInSe2(001)/GaAs(001) interface

The CuInSe2(001)/GaAs(001) interface is studied using density functional theory, where GaAs is a common substrate to grow semiconductive CuInSe2. The Se/Ga interfacial stacking is preferred based on a high work of separation of 2.085 J m−2, caused by the strong Se-Ga bonding with a bond energy of −4.22 eV. Furthermore, the interaction of intrinsic (Cu and In vacancies and antisites) and extrinsic (Ga, O, H, and C) point defects in CuInSe2 with the interface is evaluated. They segregate at the interface except from the In antisite and Ga, being a frequent dopant. CuInSe2 on GaAs exhibits a compressive strain of 1.2% so that large atoms, such as In, are not favored at the interface, minimizing the strain energy. Moreover, Ga forms stronger bonds in the bulk region than at the interface, while opposite occurs for residual gas impurities O, H, and C. These results are relevant for the transport properties of photovoltaic and thermoelectric CuInSe2 based devices.

Enhanced terahertz emission of a gallium arsenide thin film on a porous silicon distributed Bragg reflector designed at 800nm wavelength

Enhanced terahertz (THz) radiation was generated from a gallium arsenide thin film integrated on top of porous silicon distributed Bragg reflector (GaAs/PSi DBR). The film's thickness was designed to be less than the penetration depth of the 800 nm excitation source, while the PSi DBR was centered at the laser wavelength to reflect the transmitted photons at the film-substrate interface. Reflection-geometry THz time-domain spectroscopy measurement revealed enhancement in THz peak to peak amplitude by 1.67 and 5.7 times as compared to the same thickness of GaAs on silicon (GaAs/Si) and bulk semi-insulating (SI) GaAs, respectively. In comparison with the bulk SI-GaAs, both thin film samples showed an order of magnitude improvement in the THz output power. The excitation-wavelength study also revealed a maximum increase near the design wavelength. The enhancement was attributed to the high reflectivity at the film-substrate interface and optical cavity effect in GaAs. These factors contributed to an effective optical confinement within the film's THz generation region.

Photovoltaic solar cells based on graphene/gallium arsenide Schottky junction

In this article, a computational study on the photovoltaic performance and electrical characteristics of graphene/gallium arsenide Schottky junction solar cell with structure graphene/SiO2/GaAs/Au is undertaken. Graphene is used as a transparent current conducting electrode. Design and simulation of the device is carried out using Silvaco TCAD Atlas tool. Thickness of the GaAs layer is taken as 10 μm throughout the study. Under AM 1.5 G solar illumination, the device shows an open-circuit voltage (Voc) of 0.35 V, a short-circuit current density (Jsc) of 2.14 mAcm−2, and a fill factor (FF) of 69.74%, yielding a profound energy conversion efficiency (η) of 5.3%. The device exhibits an ideality factor of 1.05 along with a diode rectification ratio of 1.8 × 106. The excellent photovoltaic performance of the device is caused by the strong built-in potential in the Schottky junction, low recombination rate and the transparent nature of graphene. The effect of schottky junction formed between graphene and GaAs interface as well as the material properties on the performance of the device is demonstrated. A band diagram is proposed to explain the carrier transport phenomena.

Microscale interfacial adhesion assessment in a multilayer by a miniaturised four-point bending test

Microscale techniques capable of selectively isolating and delaminating embedded multilayer interfaces in a stable manner have the potential to be powerful characterisation tools for improving the reliability of microelectronic devices. Here we propose an analytical approach to assess the steady-state strain energy release rate during the delamination of an embedded multilayer interface, initiated by our recently developed miniaturised four-point bending technique. Stable delamination of a SiN-GaAs interface was initiated via nanoindentation induced bending of microbridges that had been milled into the surface of an Al-SiN-GaAs multilayer using a focused ion beam. Analytical models quantify the strain energy released within a section of a microbridge using the load-displacement relation obtained during delamination. The models are validated by demonstrating their capacity to approximate the experimentally observed linear-elastic deformation of a reference microbridge under both three- and four-point bending. We find that deformation of the clamped-ends as well as indenter penetration of a microbridge contribute significantly to the total indenter displacement. We then show this can be accounted for through a combination of Euler–Bernoulli beam and Hertzian contact theory. A mean steady-state strain energy release rate of G¯SS=2.20±0.36Jm−2 is obtained for the SiN–GaAs interface.