Vicinal GaAs Substrates Research Articles

Magnetization switching by spin-orbit torque in crystalline (Ga,Mn)(As,P) film deposited on a vicinal GaAs substrate

Magnetization switching by spin-orbit torque in crystalline (Ga,Mn)(As,P) film deposited on a vicinal GaAs substrate

Low‐Temperature Photoluminescence Investigation of Carbon‐Doped AlGaAs Grown by MOVPE on Vicinal Substrates

AlGaAs is promising absorber material for multi‐junction solar cells (MJSC) for its tunable bandgap to match various bandgap combination designs. However, the path to achieving high‐quality AlGaAs for solar cell application remains to be determined. In this study, we grow and characterize carbon‐doped p‐Al0.375Ga0.625As on exact and vicinal GaAs(0 0 1) substrates, using metal‐organic vapor phase epitaxy (MOVPE). Low‐temperature photoluminescence (PL) measurement is performed in the range from 6 K to 300 K. The Arrhenius plot of PL intensities reveals an increasing trend for non‐radiative recombination in conjunction with increasing miscut angle. The presence of atomic ordering that inversely correlates to the miscut angle is proposed to explain the PL linewidth and peak energy dependency on substrate orientation. The conflicting tendency of non‐radiative recombination and ordering with miscut angle are further validated using solar cell devices. A slightly vicinal substrate is recommended for AlGaAs solar cells according to our observation.

Inhomogeneity-induced high temperature ferromagnetism in n-type ferromagnetic semiconductor (In,Fe)As grown on vicinal GaAs substrates

We systematically investigate the electrical and magnetic properties of n-type ferromagnetic semiconductor (In,Fe)As thin films grown on vicinal GaAs(001) substrates with different lattice-relaxation layers and Fe-doping techniques. We show that spinodal decomposition and ferromagnetism can be enhanced in the (In,Fe)As thin films grown on InAs lattice-relaxation layers under the nucleation growth mode, while they are suppressed in those grown on the GaSb/AlSb/AlAs (from top to bottom) lattice-relaxation layers under the step-flow growth mode. We demonstrate that room-temperature ferromagnetism and good electrical properties can be obtained at the same time by using the Fe-delta-doping technique in combination with the step-flow growth mode.

Thick hydride vapor phase epitaxial growth of ZnSe on GaAs (1 0 0) vicinal and orientation patterned substrates

Zinc selenide is attractive for numerous optical applications in the mid and longwave infrared from solid state lasers to non-linear optical frequency conversion. Its use has been limited by the availability of single crystal and epitaxial materials. To meet these challenges we have developed a low-pressure hydride vapor phase epitaxy (HVPE) process for growth of high quality thick ZnSe layers on GaAs (1 0 0) vicinal and orientation-patterned GaAs (OP-GaAs) substrates. We show growth of >300 µm thick layers at growth rates >50 µm/hr. With only 0.26% lattice mismatch between ZnSe and GaAs, epitaxial layers with crystal quality comparable to bulk ZnSe substrates are achieved. X-ray reciprocal space maps show the ZnSe to be fully relaxed. Cross-sectional TEM imaging analysis shows stacking faults at the interface that propagate in to the growing film consistent with a full relaxed film. Surface morphology shows the presence of pits that have their long axis perpendicular to [1–10] direction. Low temperature photoluminescence reveals band to band emission that consisted of the 2.797 eV direct band gap along with the strong exciton emission at 2.802 eV. Growth on OP templates revealed low fidelity domains of thickness >50 µm. This work presents a process to produce high quality thick layers potentially suitable for laser and frequency conversion for defense and civilian applications.

Sn-nanothreads in GaAs matrix and their sub- and terahertz applications

We report on theoretical and experimental studies of gated GaAs structures like the field-effect transistor with an array of parallel Sn nanothreads (Sn-NTs) embedded into GaAs matrix. Two device structures are proposed and considered: the pseudomorphic HEMT (PHEMT) with a doping profile of Sn-NTs and the terahertz hot-electron bolometer (THz HEB) both fabricated on vicinal GaAs substrates. PHEMT demonstrates the anisotropy of drain-source current I∥/I⊥ ~ 2.5 at 300 K when current flows along and across Sn-NTs which we relate to formation of quasi-one-dimensional conductivity channels in InGaAs quantum well. Maximum power gain cut-off frequency fmax ~ 0.15 THz is shown. The operation of THz HEB is associated with an increase in the density of the delocalized electrons due to their heating by the incoming THz radiation. The quantum and the classical device models are developed. Since the fraction of the delocalized electrons strongly depends on the average electron energy (effective temperature), the proposed THz HEB can exhibit an elevated responsivity compared with the HEBs based on more standard heterostructures. Due to a substantial anisotropy of the device structure, the THz HEB may demonstrate a noticeable polarization selectivity of the response to the in-plane polarized THz radiation.

Investigation of multimodality effect in quantum dots InGaAs/GaAs grown by MOVPE

Self-assembled InGaAs quantum dots with In content 80% grown on vicinal GaAs substrates by MOVPE method have been investigated by photoluminescence technique in a wide range of temperatures and excitation densities. Multimodality of distribution of size and (or) shape in array of vertically stacked quantum dots synthesized under different growth conditions as well as in a single layer structure was found on the ground of appearance of a set of peaks in photoluminescence spectra at lowered temperatures. Influence of growth conditions on density and radiation wavelength of quantum dot modes has been analyzed. Investigation of photoluminescence of samples as a function of temperatures has allowed determining activation energies of three channels of the losses that were attributed to different modes of quantum dots.

Бимодальность в массивах гибридных квантово-размерных гетероструктур In-=SUB=-0.4-=/SUB=-Ga-=SUB=-0.6-=/SUB=-As, выращенных на подложках GaAs

AbstractHybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In_0.4Ga_0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.

Bimodality in Arrays of In0.4Ga0.6As Hybrid Quantum-Confined Heterostructures Grown on GaAs Substrates

Hybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In0.4Ga0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.

Effect of substrate orientation on strain relaxation mechanisms of InGaAs layer grown on vicinal GaAs substrates measured by in situ X-ray diffraction

The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6° toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6° toward the direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers.

Повышение быстродействия прибора PHEMT на основе GaAs с помощью профилированного дельта-легирования оловом

The PHEMT epitaxial structures with a doping profile in the form of tin nanowires were fabricated using vicinal GaAs substrate disoriented by 0.3° in relation to accurate orientation (100). Investigation of electron transport properties of the structures with nanowires of tin atoms on vicinal GaAs substrates have been presented. It was determined that non-optimal growth temperature of cap layers leads to degradation of electrophysical parameters of the samples and prevent forming of tin one-dimensional channels. Anisotropy of the saturation current on current-voltage characteristics was obtained when current flow along and across nanowires. Field effect transistors with special topology for orthogonal current flow were fabricated and frequency characteristics were measured. The evident anisotropy of the frequency characteristics for PHEMT was shown. Gain coefficient MSG (Maximum Stable Gain) of the fabricated PHEMT for current flow along nanowires correlates to best-achieved values of MSG for GaAs PHEMT.

Growth of lattice-matched GaInAsP grown on vicinal GaAs(001) substrates within the miscibility gap for solar cells

The growth of quaternary Ga0.68In0.32As0.35P0.65 by metal-organic vapor phase epitaxy is very sensitive to growth conditions because the composition is within a miscibility gap. In this investigation, we fabricated 1µm-thick lattice-matched GaInAsP films grown on GaAs(001) for application to solar cells. The growth temperature and substrate miscut are varied in order to characterize the effect of the surface diffusion of adatoms on the material quality of alloys. Transmission electron microscopy and two-dimensional in-situ multi-beam optical stress determine that growth temperatures of 650°C and below enhance the formation of the CuPtB atomic ordering and suppress material decomposition, which is found to occur at the growth surface. The root-mean-square (RMS) roughness is reduced from 33.6nm for 750 °C to 1.62nm for 650°C, determined by atomic force microscopy. Initial investigations show that the RMS roughness can be further reduced using increased miscut angle, and substrates miscut toward (111)A, leading to an RMS roughness of 0.56nm for the sample grown at 600°C on GaAs miscut 6° toward (111)A. Using these conditions, we fabricate an inverted hetero-junction 1.62eV Ga0.68In0.32As0.35P0.65 solar cell without an anti-reflection coating with a short-circuit current density, open-circuit voltage, fill factor, and efficiency of 12.23mA/cm2, 1.12V, 86.18%, and 11.80%, respectively.

Growth of InAs quantum dots on vicinal GaAs substrates by molecular beam epitaxy

Previous work shows the benefits of using vicinal substrates but there is currently a gap in the experimental studies of the effects under different MBE growth conditions. To fully realize controllable growth while using a vicinal substrate, we systematically explore and discuss the mechanism behind the dependence of the optical characteristics of MBE grown InAs QD ensembles with different growth parameters on a vicinal substrate. In addition, the potential improvement in optical quality with a vicinal substrate over an on-axis is demonstrated and an investigation into applying a two-step growth procedure on a vicinal substrate is conducted. Photoluminescence of the grown QD ensembles shows that increasing V/III ratio increased wavelength and decreased FWHM. Decreasing substrate temperature increased wavelength and FWHM. Utilizing the two-step growth method increased both wavelength and FWHM with increased interruption time.

Impact of vicinal GaAs(001) substrates on Bi incorporation and photoluminescence in molecular beam epitaxy-grown GaAs1−xBix

The controlled incorporation of Bi into GaAs is a key challenge to synthesizing dilute Bi materials. This work reveals the importance of the surface step density and direction on Bi incorporation. Steps in the [110] direction are demonstrated to enhance Bi incorporation, but at the cost of reduced photoluminescence intensity at a red-shifted peak position, while steps in the [1¯10] direction yield the opposite behavior. A qualitative model based on the competitive incorporation of As and Bi at different step edges is used to rationalize the observed differences in Bi incorporation.

Electron transport and optical properties of structures with atomic tin nanowires on vicinal GaAs substrates

Electron transport and optical properties are studied for structures with atomic tin nanowires (Sn-NWs) on vicinal GaAs substrates with misorientation angles of 0.3 and 3° with respect to the exact (100) orientation. Saturation-current anisotropy is revealed in the current–voltage characteristics of the samples for current flows along (‖ orientation) and across (⊥ orientation) the Sn-NWs: the current ratios I ‖/I ⊥ are ∼1.2 and ∼2.5 for homostructures and pseudomorphic high electron mobility transistor (PHEMT) structures, respectively. The effect of the pulling voltage and illumination on current oscillations is studied in real time in the case of current flows perpendicular to the Sn-NWs. Clear anisotropy of the PHEMT frequency characteristics is shown.

Influence of substrate misorientation on the photoluminescence and structural properties of InGaAs/GaAsP multiple quantum wells.

InGaAs/GaAsP multiple quantum wells (MQWs) were grown by metal-organic chemical vapor deposition on vicinal GaAs (001) substrates with different miscut angles of 0°, 2° and 15° towards [110]. The crystal structures of InGaAs/GaAsP were characterized by high-resolution X-ray diffraction and Raman spectroscopy. The surface morphologies of InGaAs/GaAsP MQWs were observed by atomic force microscopy. The mechanisms for step flow, step bunching and pyramid growth on 0°, 2° and 15° misoriented substrates were discussed. The results provide a comprehensive phenomenological understanding of the self-ordering mechanism of vicinal GaAs substrates, which could be harnessed for designing the quantum optical properties of low-dimensional systems. From low-temperature photoluminescence, it was observed that the luminescence from the MQWs grown on a vicinal surface exhibits a red-shift with respect to the 0° case. An extra emission was observed from the 2° and 15° off samples, indicating the characteristics of quantum wire and pyramidal self-controlled quantum-dot systems, respectively. Its absence from the PL spectrum on 0° surfaces indicates that indium segregation is modified on the surfaces. The relationship between InGaAs/GaAsP MQWs grown on vicinal substrates and their optical and structural properties was explained, which provides a technological basis for obtaining different self-controlled nanostructures.

Effect of the bimodality of a QD array on the optical properties and threshold characteristics of QD lasers

Heterostructures with InGaAs quantum dots (QDs) are synthesized on vicinal GaAs (001) substrates. The photoluminescence (PL) spectra and threshold characteristics of edge-emitting QD lasers are studied in the temperature range 10-400 K. The structural properties of QDs are examined by transmission electron microscopy. Analysis of the PL spectra demonstrates the bimodality of the QD array, which leads to an unusual temperature behavior of the PL spectra and threshold current density. A model of the population of a bimodal QD array by carriers, describing the observed phenomena, is considered.

Pseudomorphic HEMT with Sn nanowires on a vicinal GaAs substrate

The first pseudomorphic HEMT (PHEMT) with a doping profile of Sn nanowires (Sn-NWs) on a vicinal GaAs substrate has been demonstrated. Anisotropy of saturation current at 300 K was obtained when current flows along and across Sn-NWs. In the case of PHEMT orientation for a current flow along Sn-NWs, a higher power gain cut-off frequency was observed in comparison with PHEMT orientation for a current flow perpendicular to Sn-NWs (). We relate the obtained anisotropy of the static and dynamic characteristics of PHEMT to the formation of quasi-one-dimensional conductivity channels in a quantum well.

Sn doping in thermoelectric Bi2Te3 films by metal-organic chemical vapor deposition

Sn-doped Bi2Te3 films were grown on vicinal GaAs (001) substrates by metal-organic chemical vapor deposition at 360°C. Trimethylbismuth and diisopropyltellurium, which are alkyl-based, were used as the Bi and Te sources, respectively. Tetrakis(dimethylamino)tin (TDMASn) and tetramethyltin (TMSn) were used as the Sn precursors. Both Sn precursors successfully converted the carrier type of the Bi2Te3 films from n- to p-type and achieved a high Seebeck coefficient. In the case of the Sn-doped Bi2Te3 films with TDMASn, however, the Sn concentration could not be monotonically controlled by the amount of the precursor, and even the hole concentration was almost invariant despite the drastic increase in the amount of the precursor. In the case of the Sn-doped Bi2Te3 films grown with TMSn, on the other hand, the Sn and hole concentrations could be easily controlled by the variation in the flow rate of the H2 carrier gas. In particular, the hole concentration varied over a range of 1–5×1019/cm3 in which a thermoelectric power factor can be maximized despite a very high vapor pressure of TMSn. The growth of high-quality Sn-doped Bi2Te3 films was possible using all alkyl-based precursors.

Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction

High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3 topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

Mechanism of self-assembled growth of ordered GaAs nanowire arrays by metalorganic vapor phase epitaxy on GaAs vicinal substrates

We report the self-catalyzed growth of GaAs nanowire arrays by metalorganic vapor phase epitaxy (MOVPE) on GaAs vicinal substrates. The effect of substrate misorientation on the nanowire growth and the influence of growth parameters such as temperature and input V/III ratio have been studied in detail. Variation in the nanowire growth mechanism and consequential changes in the nanowire growth morphology were observed. A VLS growth mechanism with negligible effect of the vicinal surface gave rise to randomly distributed droplet-terminated GaAs nanowires at 400 °C and multiprong root-grown GaAs nanowire clusters at 500 °C with low V/III ratio. The substrate misorientation effect was dominant at 500 °C with higher V/III ratio, in which case the combined effect of the vicinal surface and the self-catalyzed Ga droplets assisted the realization of self-assembled and crystallographically oriented epitaxial nanowire arrays through the vapor–solid mechanism.