Growth Of GaAs Research Articles

Исследование элементарных процессов МOC-гидридной эпитаксии наногетероструктур на основе арсенида галлия методом атомно-силовой микроскопии

Using atomic force microscopy, we studied the elementary processes of growing (Al, Ga, In) As heterostructures on misoriented GaAs (001) substrates by the method of MOC hydride epitaxy under reduced pressure. It was established that the growth of the epitaxial layers of GaAs and AlGaAs occurs according to a layered mechanism with the formation of macrosteps. The growth of pseudomorphic InGaAs / GaAs (001) layers also occurs by a layered mechanism with the formation of macrosteps. However, if the thickness of the pseudomorphic InxGa1-xAs / GaAs (001) layer exceeds a certain critical value depending on the molar fraction of InAs in the composition of the solid solution (x), the formation of growth defects in the form of three-dimensional islands, the density of which increases with increasing thickness, is observed on the surface of the InGaAs layer InGaAs layer. The formation of three-dimensional InGaAs islands is associated with the relaxation of elastic stresses in the pseudomorphic InGaAs / GaAs (001) layer according to the Stranski-Krastanov mechanism. Keywords: gallium arsenide, AlGaAs, InGaAs, MOC hydride epitaxy, defect formation, Stranski-Krastanov mechanism.

Growth of GaAs on single-crystal layered-2D Bi2Se3

Abstract This work demonstrates the successful growth of cubic GaAs (111) on single-crystal 2D layered Bi2Se3 (0001) substrates achieved using a cubic ZnSe buffer layer. This growth sequence was chosen based upon observed reactions between Bi2Se3 (0001) substrates and both Ga and Zn. For the conditions used in our MOCVD reactor, triethylgallium (TEGa) interacts strongly with Bi2Se3 to form Ga2Se3, which can disrupt the nucleation and growth of GaAs. Therefore, a buffer layer is needed which prevents Ga–Bi2Se3 interactions while simultaneously providing a suitable growth surface for GaAs. ZnSe was chosen because it is lattice-matched to GaAs, and can be created by annealing the Bi2Se3 under a diethylzinc (DEZn) flux. A sample utilizing this growth sequence has been grown, characterized and exfoliated as a possible pathway toward reducing the substrate cost for III-V devices such as solar cells.

Influence of two-stage growth during the formation of GaAs/Si heterostructures for the creation of optoelectronic devices

The development of GaAs/Si heterostructures can be an important stage for use as solar cells, LEDs and lasers based on silicon substrates. At present, A3B5 compounds grown epitaxial on Si substrates are of great interest because of the monolithic integration of optoelectronic devices with Si-based microelectronics. High-quality epitaxial growth of heterostructures will not only ensure high mobility of the carrier materials, but also preserve the advantages of lightweight and inexpensive Si substrates with high mechanical strength and excellent thermal parameters. However, obtaining A3B5 compounds with high quality crystals of GaAs/Si heterostructures is a difficult task due to the formation of an antiphase domain boundary as a result of the growth of polar GaAs on a non-polar Si substrate. Because of this, a high density of penetrating dislocations arises due to the mismatch of the lattice parameters (4.1%), as well as the coefficient of thermal expansion (62%).

Room-temperature photoluminescence of AP-MOVPE grown single GaSb/GaAs quantum dot layer

The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots (QDs) was investigated. Room temperature (RT) photoluminescence (PL) emission was achieved from single layers of quantum dots by controlling the GaAs host matrix growth temperature. Samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. The hole localisation energy determined for these samples at RT was approximately 470 meV.

Impact of Bi incorporation on the evolution of microstructure during growth of low-temperature GaAs:Bi/Ga(As,Bi) layers

Complex morphology is observed in the GaAs:Bi cap layer of Ga(As,Bi) films grown on GaAs(001) substrates by low-temperature (LT) molecular beam epitaxy (MBE). The microstructure is dominated by the presence of V-shaped domains in the LT-GaAs cap layer and by the (unintentional) inhomogeneous incorporation of Bi from the underlying Ga(As,Bi) layer growth. Aberration-corrected scanning transmission electron microscopy techniques enabled two types of domain to be identified: (i) twinned domains and (ii) Bi-rich atomically ordered domains with triple periodicity. The observed microstructure is discussed in the context of LT-MBE growth in combination with the presence of a small amount of Bi, which seemingly alters adatom diffusivity. Surface processes and (surface) kinetic factors play a key role in the resultant morphology and explain the appearance of both types of domains.

Shape, Size Evolution, and Nucleation Mechanisms of GaAs Nanoislands Grown on (111)Si by Low-Temperature Metal–Organic Vapor-Phase Epitaxy

The shape, size evolution, and nucleation mechanisms of GaAs nanoislands grown at 400 °C on As-stabilized (111)Si by metal–organic vapor phase epitaxy are reported for the first time. GaAs crystallizes in the zincblende phase in the very early nucleation stages until a continuous epilayer is formed. GaAs nanoislands grow (111)-oriented on Si as truncated hexagonal pyramids, bound by six equivalent {120} side facets and a (111) facet at the top. Their diameter and height appear to increase linearly with the deposition time, yielding a constant aspect ratio of ∼1/4. The nanoisland density (before coalescence) stays constant with time at ∼2 × 1010 cm–2, suggesting that the nucleation occurs at specific Si surface sites (defects) during the very early growth stages, rather than being due to the continuous formation of new nuclei. To understand the molecular-level mechanisms driving the low-temperature MOVPE growth of GaAs on Si, we applied a deposition–diffusion–aggregation (DDA) nucleation model, which predicts a linear evolution of the overall GaAs growth rate with surface coverage, in good agreement with experimental observations, under the assumption that direct impingement of trimethylgallium (Me3Ga) molecules onto the nanoisland surface dominates the material nucleation and growth rate; the contribution of Me3Ga adsorbed onto the As-stabilized (111)Si is negligible, pointing out the reduced reactivity of the Si surface (As passivation). Our DDA model allows estimation of the effective reactive sticking coefficient of Me3Ga onto GaAs, which is equal to 2.82 × 10–5: the small value is compatible with the Me3Ga large steric hindrance and the competitive role of methyl radicals in surface adsorption at low temperature.

An innovative approach for controlled epitaxial growth of GaAs in real MOCVD reactor environment

In present paper, the off-lattice homoepitaxy of GaAs over (100) GaAs substrate crystal is reported. The innovative inhouse developed numerical technique exploiting atomic scale kinetic Monte Carlo algorithms for simulation of thin film deposition is used to replicate the MOCVD reactor based epi-growth with appropriate reactor's input conditions. The epi-growth mechanism includes adsorption, diffusion and desorption processes depending upon different energies. The lattice parameter, roughness and strain of epi-grown layer have been extracted and energy-wave vector (E-k) dispersion relation has been simulated with empirical pseudopotential method using lattice constant extracted from epi-grown film. The results obtained on the basis of proposed simulation has been compared and contrasted against experimental results. The study of growth rates at different partial pressure of TMG precursor and at fixed partial pressure of TBAs precursor depicts the linear growth rate. The slope of epi-growth rates has been obtained 5.78 with respect to partial pressure. The curve for roughness shows linear increase initially which later flattens and becomes almost constant. Low values of strain extracted for initial layers because of some randomness prevalent in KMC. The energy band gap value of epi-grown GaAs thin film over GaAs is extracted 1.44eV.

Crystalline GaAs Thin Film Growth on a c-Plane Sapphire Substrate

Crystalline zinc blende GaAs has been grown on a trigonal c-plane sapphire substrate by molecular beam epitaxy. The initial stage of GaAs thin film growth has been investigated extensively in this paper. When grown on c-plane sapphire, it takes (111) crystal orientation with twinning as a major problem. Direct growth of GaAs on sapphire results in three-dimensional GaAs islands, almost 50% twin volume, and a weak in-plane correlation with the substrate. Introducing a thin AlAs nucleation layer results in complete wetting of the substrate, better in-plane correlation with the substrate, and reduced twinning to 16%. Further, we investigated the effect of growth temperature, pregrowth sapphire substrate surface treatment, and in-situ annealing on the quality of the GaAs epilayer. We have been able to reduce the twin volume below 2% and an X-ray diffraction rocking curve line width to 223 arcsec. A good quality GaAs on sapphire can result in the implementation of microwave photonic functionality on a photonic chip.

Gallium arsenide solar cells grown at rates exceeding 300\u2009\xb5m\u2009h\u22121 by hydride vapor phase epitaxy

We report gallium arsenide (GaAs) growth rates exceeding 300 µm h−1 using dynamic hydride vapor phase epitaxy. We achieved these rates by maximizing the gallium to gallium monochloride conversion efficiency, and by utilizing a mass-transport-limited growth regime with fast kinetics. We also demonstrate gallium indium phosphide growth at rates exceeding 200 µm h−1 using similar growth conditions. We grew GaAs solar cell devices by incorporating the high growth rate of GaAs and evaluated its material quality at these high rates. Solar cell growth rates ranged from 35 to 309 µm h−1 with open circuit voltages ranging from 1.04 to 1.07 V. The best devices exceeded 25% efficiency under the AM1.5 G solar spectrum. The high open-circuit voltages indicate that high material quality can be maintained at these extremely high growth rates. These results have strong implications toward lowering the deposition cost of III-V materials potentially enabling the deposition of high efficiency devices in mere seconds.

GaAs (1 1 1) epilayers grown by MBE on Ge (1 1 1): Twin reduction and polarity

We perform the growth of GaAs (111) epilayers on nominal Ge(111) wafers by molecular beam epitaxy (MBE). The polarity of GaAs is (111)A and homongeneous over the full area, as measured by transmission electron microscopy and high energy electron diffraction. This orientation conflicts with the common growth model for GaAs on Ge(111). Twinned domains are the main defects in our GaAs (111) epilayers. Using cathodoluminescence, we observe that some twin boundaries hold large number of non-radiative recombination centers. During growth, we find that only a narrow domain of As:Ga ratios lead to the growth of smooth and twin-free GaAs (111)A epilayers. At low As:Ga ratio, the surface is rough; while at high As:Ga ratio the epilayers present large densities of twinned domains.

Uniformity of GaAs solar cells grown in a kinetically-limited regime by dynamic hydride vapor phase epitaxy

We demonstrate solar cell devices grown on 50 mm diameter GaAs substrates by dynamic hydride vapor phase epitaxy (D-HVPE). In contrast to our prior D-HVPE devices, grown at 650 °C in a transport-limited regime, these devices were grown at 700 °C in a kinetically-limited growth regime in which the growth rate uniformity is controlled by thermally-activated surface reactions. These devices exhibit open-circuit voltages up to 1.07 V, nearly identical performance to the devices grown at lower temperature in a different growth regime. We evaluate the uniformity of device performance and find only a 1% variation in absolute, device efficiency across the majority of the wafer in devices without anti-reflection coating. We analyze the GaAs and GaInP thickness uniformity and GaInP compositional uniformity, using high-tresolution x-ray diffraction mapping, and find that any non-uniformity in device efficiency is not related to variations in these structural parameters. We combine three-dimensional computational fluid dynamics modeling of our reactor with a kinetic model for GaAs growth, and use the combined model to predict spatial GaAs growth rate over a 50 mm wafer area. We compare these predictions with experimental data from our D-HVPE reactor and find excellent agreement. We use the model to the gain insight into the specific mechanisms that control GaAs spatial uniformity in the kinetically-limitedgrowth regime. These results suggest a large parameter window for the growth of high-performance optoelectronic devices by D-HVPE, possibly with large area uniformity.

X-ray photoelectron spectroscopy study of Ga nanodroplet on silica-terminated silicon surface for nanowire growth

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

An algorithm for the in situ analysis of optical reflectance anisotropy spectra

We report on a computer algorithm for the in situ analysis of reflectance anisotropy (RA) spectra in a time frame compatible with the epitaxial growth of cubic semiconductors. This algorithm allows for the in situ acquisition of RA spectra and their decomposition into two components whose amplitude depends on the As coverage of the semiconductor surface. One of such components is associated with the surface orthorhombic strain due to the surface reconstruction and has an amplitude that strongly depends with surface reconstruction and thus As coverage. This fact opens the possibility of using reflectance anisotropy spectroscopy (RAS) as an optical probe to characterize the As surface coverage in real time. To demonstrate the performance of the algorithm we report on RA measurements carried out during the homoepitaxial growth of GaAs (001). We show that the algorithm is capable of analyzing a set of 500 RA spectra in a time span of about 10 s. This allows for a range of applications for the developed algorithm, including the surface characterization and fine tuning of the substrate stoichiometry just before epitaxial growth, during the growth of the buffer layer.

Anti-phase domain induced morphological differences of self-assembled InSb/GaAs quantum dots grown on (0 0 1) Ge substrate

The effects of growth temperature, growth rate and local growth position on the morphology of self-assembled InSb/GaAs quantum dots (QDs) on (0 0 1) Ge substrate are investigated. It is found that for low growth rates, anti-phase domain (APD) boundaries formed during the growth of GaAs on Ge can effectively act as the preferential nucleation position of InSb QDs. For high growth rates, InSb/GaAs QDs nucleate on both the APD boundary and the APD surface, leading to high density-InSb QDs. The QD morphologies on the APD boundary and the APD surface are distinctly different. The roles of growth rate and local growth position on the morphology of realized QDs are described. By varying the growth conditions, low density and locally aligned QDs as well as high density InSb QDs can be obtained.

Molecular beam epitaxy growth and temperature-dependent electrical characterization of carbon-doped GaAs on GaAs(1 1 1)B

Here we present a study of the solid source molecular beam epitaxy growth of carbon doped GaAs(1 1 1)B oriented layers in a wide doping concentration range from 1016 to 1020cm-3. The layers have been fabricated on GaAs(1 1 1)B substrates with a 1° miscut towards (2 1 1) and carbon was supplied by a heated graphite filament source. Atomic force microscopy revealed smooth surfaces (root mean square roughness 0.3 nm) up to the highest carbon concentration. The carbon concentration was determined by secondary ion mass spectroscopy. All samples exhibit p-type conductivity and temperature-dependent Hall- and resistivity measurements show carrier freeze out for doping concentration in the 1016 cm−3 and 1017 cm−3 range, whereas we observe degenerated behavior for carbon concentrations above ca. 1×1019 cm−3. The hole mobility decreases with increasing carbon concentration. The acceptor ionization energy for carbon was determined via low-temperature photoluminescence measurements to 26.3 meV. From the free hole density determined from Hall-measurements at 300 K and the overall carbon concentration, we estimate that approximately 100% of the carbon atoms are electrically active acceptors for carbon concentrations below 1×1018 cm−3. For concentrations above 1×1019 cm−3 compensation sets in and the doping efficiency is well below 100%. For comparison, samples in the standard (1 0 0)-orientation have been produced and carbon incorporation behavior during growth is very similar.

Real-time structural analysis of InGaAs/InAs/GaAs(1 1 1)A interfaces by in situ synchrotron X-ray reciprocal space mapping

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

Buffer free InGaAs quantum well and in-plane nanostructures on InP grown by atomic hydrogen assisted MBE

We investigate the optical and electrical properties of InGaAs thin films and nanostructures grown directly on an InP semi-insulating substrate without any buffer layer using atomic hydrogen assisted molecular beam epitaxy. We confirm the positive influence of the atomic hydrogen flux during the deoxidization process as well as during the growth itself improving the photoluminescence properties of InGaAs quantum wells. We also study the effect of the atomic hydrogen flux on the electrical properties of buffer free undoped, Te or Si doped InGaAs epilayers. Eventually, we demonstrate that atomic hydrogen flux can be used to achieve InGaAs growth selectivity with respect to a SiO2 mask for a growth temperature as low as 470 °C and obtain in-plane InGaAs nanostructures on InP with good transport properties.

Real-Time Observation of In Segregation During InGaAs Growth on GaAs(001) by X-ray Diffraction

Real-Time Observation of In Segregation During InGaAs Growth on GaAs(001) by X-ray Diffraction

Terahertz Emission of Gallium Arsenide on Textured p-type Silicon (100) Substrates Grown via Molecular Beam Epitaxy

This study presents the terahertz (THz) emission of molecular beam epitaxy (MBE)-grown Gallium Arsenide (GaAs) on surface textured p-type Silicon (p- Si) (100) substrates. Surface texturing was achieved by anisotropic wet chemical etching using 5% wt Potassium Hydroxide (KOH): Isopropyl alcohol (IPA) (50:1) solution for 15, 30, 45, and 60 minutes. Reflectivity measurements for the textured p-Si(100) substrates indicated that the overall texturing increases with longer etching times. Raman spectroscopy of the post-growth samples confirmed GaAs growth. The THz emission intensities were the same order of magnitude. The GaAs grown on p-Si(100) textured for 60 minutes exhibited the most intense THz emission attributed to the increased absorption from a larger surface-to-volume ratio due to surface texturing. All GaAs on textured p-Si(100) samples had frequency bandwidth of ~2.5 THz.

High throughput MOVPE and accelerated growth rate of GaAs for PV application

We present the feasibility of metalorganic vapor phase epitaxy (MOVPE) with extremely high-speed growth of GaAs for solar cell applications. The growth rate was increased up to 120 μm/h, and exhibited an almost linear relationship with the amount of supplied trimethylgallium (TMGa). The thickness variation and doped carrier concentration of GaAs grown at 90 μm/h were comparable to those of conventionally grown GaAs at a lower growth rate. The potential for reducing the V/III supply ratio was investigated to reduce the material cost. Non-doped GaAs wafers were grown at the accelerated growth rate of 90 μm/h, with various V/III ratios. The growth rate of GaAs increased by 20% when the V/III ratio was decreased from 40 to 5. In low temperature photoluminescence (PL) measurement, significant change in PL spectra was not observed, indicating that there was no significant change in quality. The light-power conversion efficiency was almost comparable for V/III ratios from 10 to 40 whereas that at the lowest V/III ratio of 5 was degraded. Photovoltaic (PV) solar cells of GaAs were fabricated with various growth condition. It is found that the performance of the cells grown at 90 μm/h were comparable with previous results.