Growth Of GaAs Research Articles

Impact of low-temperature cover layer growth of InAs/GaAs quantum dots on their optical properties

The effect of low-temperature InGaAs/GaAs cover layer growth of InAs quantum dots on their optical and structural properties was investigated. Photoluminescence intensity depended heavily on the growth temperature and thickness of the low-temperature cover layer and decreased as the number of dislocations formed directly above InAs quantum dots increased. These dislocations are formed at the initial stage of high-temperature GaAs growth, originating from pits that remain on the surface after the growth of the low-temperature cover layer and subsequent annealing. To ensure a high-quality InAs quantum dot structure free from dislocations, it is important to obtain a highly flat surface with suppressed pits after low-temperature cover layer growth and subsequent annealing.

Consideration of the Intricacies Inherent in Molecular Beam Epitaxy of the NaCl/GaAs System.

The high cost of substrates for III–V growth can be cost limiting for technologies that require large semiconductor areas. Thus, being able to separate device layers and reuse the original substrate is highly desirable, but existing techniques to lift a film from a substrate have substantial drawbacks. This work discusses some of the complexities with the growth of a water-soluble, alkali halide salt thin film between a III–V substrate and overlayer. Much of the difficulty stems from the growth of GaAs on an actively decomposing NaCl surface at elevated temperatures. Interestingly, the presence of an in situ electron beam incident on the NaCl surface, prior to and during GaAs deposition, affects the crystallinity and morphology of the III–V overlayer. Here, we investigate a wide range of growth temperatures and the timing of the impinging flux of both elemental sources and high energy electrons at different points during the growth. We show that an assortment of morphologies (discrete islands, porous material, and fully dense layers with sharp interfaces) and crystallinity (amorphous, crystalline, and highly textured) occur depending on the specific growth conditions, driven largely by changes in GaAs nucleation which is greatly affected by the presence of the reflection high energy electron diffraction beam.

Benchtop Electrochemical Growth and Controlled Alloying of Polycrystalline InxGa1–xAs Thin Films

Compared to Si, GaAs offers unique material advantages such as high carrier mobility and energy conversion efficiency, making GaAs a leading competitor to replace Si on several technological fronts related to optoelectronics and solar energy conversion. Alloying the GaAs lattice with elemental In allows the direct bandgap of the resulting ternary alloy to be tuned across the near-infrared (NIR) region of the electromagnetic spectrum from ∼0.9 to 3.5 μm. However, methods of fabricating high-quality crystalline GaAs are currently limited by their high cost and low throughput relative to Si growth methods, suggesting the need for alternative low-cost routes to GaAs growth and alloying. This research documents the first instance in the literature of the electrodeposition and controlled alloying of polycrystalline InxGa1–xAs films at ambient pressure and near-room temperature using the electrochemical liquid–liquid–solid (ec-LLS) process. X-ray diffraction and Raman spectroscopy support the polycrystalline growth of (111)-oriented InxGa1–xAs films. Consistent redshifts of the GaAs-like TO peaks were observed in the Raman data as the In composition of the liquid metal electrode was increased. Optical bandgaps, determined via diffuse reflectance measurements, displayed a consistent decrease with the increase in the In composition of InxGa1–xAs films. While Raman, diffuse reflectance, and energy-dispersive X-ray spectroscopy data support controlled alloying efforts, all techniques suggest an overall decrease of the In/Ga ratios present in deposited films relative to those of the liquid metal electrodes. These results lend support for the continued development of ec-LLS as a viable method of achieving crystalline growth and alloying of binary and ternary semiconductor material systems using a benchtop setup under ambient pressure and near-room temperature.

Molecular‐Beam Epitaxy Growth and Properties of AlGaAs Nanowires with InGaAs Nanostructures

Combinations of III–V nanowires (NWs) with quantum dots (QDs) are promising building blocks for quantum light sources. Herein, for the first time, the results of growing AlGaAs NWs with InGaAs QDs by molecular‐beam epitaxy on a silicon substrate are shown. The optimal growth temperature is determined and the physical properties of the grown nanostructures are studied. It is shown that the grown nanostructures exhibit photoluminescence (PL) signal up to room temperature in a wide wavelength range, including 1.3 μm emission which is important for the optical fiber transmission. It is found that in addition to InGaAs QDs radial InGaAs quantum wells are formed inside the NWs as a result of lateral/axial InGaAs growth competition. The proposed technology opens up new possibilities for the integration of direct‐band III–V materials with the silicon platform for various applications in the field of silicon photonics and quantum communication technology.

Simulating Vapor-Liquid-Solid Growth of Au-Seeded InGaAs Nanowires.

Ternary III-V nanowires are commonly grown using the Au-seeded vapor-liquid-solid method, wherein the solid nanowires are grown from nanoscale liquid seed particles, which are supplied with growth species from the surrounding vapor phase. A result of the small size of these seed particles is that their composition can vary significantly during the cyclical layer-by-layer growth, despite experiencing a constant pressure of growth species from the surrounding vapor phase. Variations in the seed particle composition can greatly affect the solid nanowire composition, and these cyclical dynamics are poorly understood for ternary nanowire growth. Here, we present a method for simulating nanowire growth which captures the complex cyclical dynamics using a kinetic Monte Carlo framework. In the framework, a nanowire grows through the attachment or detachment of one III-V pair at the time, with rates that are based on the momentary composition of the seed particle. The composition of the seed evolves through the attachment and detachment of III-V pairs to the solid nanowire and through the impingement or evaporation of single atoms to the surrounding vapor. Here, we implement this framework using the As-Au-Ga-In materials system and use it to simulate the growth of Au-seeded InGaAs nanowires with an average solid Ga/III ratio around 0.5. The results show that nucleation preferentially occurs via clusters of InAs and that the compositional hierarchy of the liquid seed (X As < X Ga < X In) determines much of the dynamics of the system. We see that imposing a constraint on the simulation, that only the most recently attached III-V pair can be detached, resulted in a significant narrowing of the compositional profile of the nanowire. In addition, our results suggest that, for ternary systems where the two binaries are heavily mismatched, the dynamics of the seed particle may result in an oscillating compositional profile.

Enhanced Radiative Efficiency of InGaAs/GaAsP Multiple Quantum Wells by Optimizing the Thickness of Interlayers

InGaAs/GaAsP multiple quantum wells (MQWs) are used in electronic devices because the high radiative efficiency of MQWs improves the device performance. To realize high radiative efficiency, a GaAs interlayer is inserted to decrease the defects at the heterointerface between the well and barrier of the MQWs. However, it is unclear how the interlayer thickness and insertion position affect the radiative efficiency of the MQWs. Herein, the influence of the GaAs interlayer thickness on the radiative efficiency by measuring the photoluminescence of MQWs with different interlayer thicknesses is investigated. A thicker GaAs interlayer below the InGaAs enhances the radiative efficiency. Moreover, the GaAs interlayer above the InGaAs must be thicker than ≈6 nm to enhance the radiative efficiency. The initial growth of GaAs above the InGaAs degrades the surface morphology, which may be associated with the carry‐over of indium on the InGaAs surface and may generate defects between the InGaAs and GaAsP layers. The surface of sufficiently thick GaAs interlayers has a flatter morphology and is free from the degradation of radiative efficiency. The results suggest inserting of interlayers with a smooth surface morphology between strained layers during epitaxial growth is an effective method to suppress nonradiative recombination.

Исследование особенностей эпитаксиального роста GaAs на подложках Si, модифицированных фокусированными ионными пучками

In this paper, we present a study of the effect of the silicon substrate modification by focused ion beams on subsequent growth of GaAs layers by molecular beam epitaxy. We demonstrate that when samples exposed to the ion irradiation at various accelerating voltages and ion beam passes are annealed in the absence of the arsenic flux, an increase in the depth of the modified Si substrate areas occurs. At the same time, crystallization of gallium accumulations during annealing in the arsenic flux leads to the filling of holes formed during the ion bombardment. We reveal that the growth of GaAs on substrates with areas modified at an accelerating voltage of 30 kV and subjected to subsequent annealing in the arsenic flux at a temperature of 600 °C is accompanied by the formation of nanowires, the density of which increases within areas with a large number of ion beam passes. The results of the conducted research can be used for the development of technological approaches to the formation of GaAs epitaxial layers on Si substrates.

Growth of GaAs-=SUB=-1-x-=/SUB=-Bi-=SUB=-x-=/SUB=- layers by molecular-beam epitaxy

By molecular-beam epitaxy we have grown epitaxial layers of GaAs1-xBix solid solutions with a bismuth content of 0&lt;x&lt;0.02. Structural and optical properties of the layers were investigated. We determine the influence of the bismuth flux and substrate temperature on the bismuth incorporation into the growing layers. Keywords: gallium arsenide, bismuth, molecular-beam epitaxy, bandgap.

Study of GaAs epitaxial growth on Si substrates modified by focused ion beams

In this paper, we present a study of the effect of the silicon substrate modification by focused ion beams on subsequent growth of GaAs layers by molecular beam epitaxy. We demonstrate that when samples exposed to the ion irradiation at various accelerating voltages and ion beam passes are annealed in the absence of the arsenic flux, an increase in the depth of the modified Si substrate areas occurs. At the same time, crystallization of gallium accumulations during annealing in the arsenic flux leads to the filling of holes formed during the ion bombardment. We reveal that the growth of GaAs on substrates with areas modified at an accelerating voltage of 30 kV and subjected to subsequent annealing in the arsenic flux at a temperature of 600oC is accompanied by the formation of nanowires, the density of which increases within areas with a large number of ion beam passes. The results of the conducted research can be used for the development of technological approaches to the formation of GaAs epitaxial layers on Si substrates. Keywords: molecular beam epitaxy, monolithic integration, gallium arsenide, silicon, focused ion beams.

Three-step Epitaxial Growth of GaAs on Si by MOCVD echnology

Three-step Epitaxial Growth of GaAs on Si by MOCVD echnology

Study of the initial stage of GaAs growth on FIB-modified silicon substrates

In this work, we studied the effect of the deposition thickness, growth rate, arsenic flux, and implantation dose on the morphology of the GaAs nanostructures grown on modified Si areas. It is shown that an increase in the growth rate at the initial stages of the growth process leads to the transition of the growth regime from layered-like to one-dimensional with the formation of nanowires. Studies of the effect of As4 pressure have shown that a change in the equivalent As4 flux in the range of 3.7 - 5.0 ML/s does not lead to any significant change in the structure of the GaAs layer in the modified areas. An increase in the implantation dose during processing with a focused ion beam led to disordering of the directions of the grown nanowires due to the degradation of the substrate crystal structure.

Revealing the Significance of Catalytic and Alkyl Exchange Reactions during GaAs and GaP Growth by Metal Organic Vapor Phase Epitaxy

Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) are getting more and more established as group V precursors for the growth of V/III semiconductors by metal organic vapor phase epitaxy (MOVPE). Due to this development, the thermal decomposition of these precursors was studied during the growth of GaAs and GaP utilizing the Ga precursors, trimethylgallium (TMGa), triethylgallium (TEGa), and tritertiarybutylgallium (TTBGa), in a horizontal AIXTRON AIX 200 GFR MOVPE system. The decomposition and reaction products were measured in line with a real-time Fourier transform quadrupole ion trap mass spectrometer from Carl Zeiss SMT GmbH. The decomposition temperatures and the related activation energies were determined for all the mentioned precursors under comparable reactor conditions. The decomposition curves suggest, on the one hand, a catalytic effect of the GaAs surface on the decomposition of TBAs. On the other hand, the decomposition products indicate alkyl exchange as a relevant step during the bimolecular decomposition of TBAs and TBP with the Ga precursors TMGa, TEGa, and TTBGa. The catalytic reaction reduces the decomposition temperature of TBAs and TBP by up to 200 °C. In addition, for the growth of GaAs with TBAs and TEGa and for the growth of GaP with TBP and TEGa, a significant decrease of the decomposition temperature with an increasing V/III ratio is observed. This behavior, which is related to an alkyl exchange reaction, gives insights into the low-temperature growth of GaAs and GaP and is converted into an effective V/III ratio. Finally, the growth of GaAs with TTBGa and TBAs is realized at 300 °C below the unimolecular decomposition temperature of TBAs, underlining the catalytic effect of the GaAs surface. Altering the growth surface with trimethylbismuth led to the prevention of the catalytic effect.

Theoretical and experimental study on epitaxial growth of antiphase boundary free GaAs on hydrogenated on-axis Si(001) surfaces

The formation of double-layer atomic steps on Si(001) surfaces is an efficient way to eliminate the antiphase boundaries (APBs) on GaAs/Si(001) interfaces. The surface energy of on-axis Si(001) surfaces with different atomic step structures was calculated and analyzed from the first principles. An optimal hydrogen-annealing process condition, the hydrogen pressure of 800 mbar and the annealing temperature of 800 °C for 10 min, was obtained experimentally. Under this annealing condition, a 420 nm APB-free GaAs epitaxial layer grown on on-axis Si(001) substrates was achieved by metal-organic chemical vapor deposition. The effect of the annealing temperature on the APB density of the GaAs/Si(001) samples was explained from the aspects of thermodynamics and kinetics. It is of great significance to optimize the growth conditions of APB-free III–V epitaxial materials on on-axis Si(001) surfaces for the large-scale silicon monolithic integration of optoelectronic devices.

Growth-related photoluminescence properties of InSb/GaAs self-assembled quantum dots grown on (001) Ge substrates

Various photoluminescence (PL) spectroscopies are applied to reveal the growth-related properties of self-assembled InSb/GaAs quantum dots (QDs) grown on (001) Ge substrate. Obtained QDs have rectangular-based shape and mainly locate near GaAs antiphase domain boundaries (APBs), which are formed during the growth of GaAs on (001) Ge substrate. The morphology and structural properties of InSb QDs can be varied by the change of controlled growth conditions. Optical phonons scatterings of the embedded InSb QDs are revealed by Raman spectroscopy. The low-temperature PL emission energy of InSb/GaAs QDs is in the range of 1.18–1.29 eV. The power-dependent PL spectroscopy confirms the type-II band alignment in this system. The thermal activation energies (22.7 meV and 146.5 meV) are extracted from the temperature-dependent PL spectroscopy (10–140 K). The polarization-dependent PL spectroscopy is performed and exhibits the polarization degree of ~ 18%, which is attributed to the shape anisotropy of buried InSb QDs.

Bufferless Epitaxial Growth of GaAs on Step-Free Ge (001) MesaSupported by the National Natural Science Foundation of China (Grant Nos. 61975230, 61635011, 61804177 and 11804382), the National Key Research and Development Program of China (Grant No. 2018YFB2200104), Beijing Municipal Science and Technology Commission (Grant No. Z191100004819010), and the Key Research Program of Frontier Sciences, CAS (Grant No. QYZDB-SSW-JSC009).

GaAs/Ge heterostructures have been employed in various semiconductor devices such as solar cells, high-performance CMOS transistors, and III–V/IV heterogeneous optoelectronic devices. The performance of these devices is directly dependent on the material quality of the GaAs/Ge heterostructure, while the material quality of the epitaxial GaAs layer on the Ge is limited by issues such as the antiphase domain (APD), and stacking-fault pyramids (SFP). We investigate the epitaxial growth of high-quality GaAs on a Ge (001) mesa array, via molecular beam epitaxy. Following a systematic study of the Ge terrace via an in situ scanning tunneling microscope, an atomically step-free terrace on the Ge mesa measuring up to 5 × 5 μm2 is obtained, under optimized growth conditions. The step-free terrace has a single-phase c (4 × 2) surface reconstruction. The deposition of a high-quality GaAs layer with no APD and SFP is then achieved on this step-free Ge terrace. High-resolution transmission electron microscopy and electron channel contrast image characterizations reveal the defect-free growth of the GaAs layer on the step-free Ge mesa. Furthermore, InAs quantum dots on this GaAs/Ge mesa reveal photoluminescent intensity comparable to that achieved on a GaAs substrate, which further confirms the high quality of the GaAs layer on Ge.

Surface morphology evolution and underlying defects in homoepitaxial growth of GaAs (110)

The evolution of the surface morphology and underlying pyramidal defects in homoepitaxial GaAs (110) layers was investigated with respect to the layer thickness up to 1 µm. Ga and As atoms coexisting in a one-to-one atomic ratio on the (110)-oriented GaAs surface exhibit different incorporation rates and adatom migration rates, giving rise to local As atomic disordering in the epitaxial layer. Accordingly, this disordering triggers distinctive shapes of three-dimensional surface islands composed of specific facets and underlying microtwins. Single triangular-shaped islands initially appear at an early stage of epitaxial growth. With increasing layer thickness, all of the single triangular islands suddenly become paired triangular islands by forming secondary single triangular islands nearby, like decalcomania. A further increase of the layer thickness induces a complete transformation into four-legged starfish shapes containing directional side edges. At this stage, the underlying pyramidal defects of the surface islands are filled with {111} microtwins. Surprisingly, the evolutions of island shapes and underlying twin formation are closely associated with the strain relaxation in the thick GaAs (110) layers, which is unexpected in any homoepitaxial system. We found that a higher growth temperature retards the shape evolution of surface islands, leading to suppression of compressive strain.

Evolution of Pore Growth in GaAs in Transitory Anodization Regime from One Applied Voltage to Another

The paper reports the results of investigation of the pore growth during anodic etching of (111)-oriented wafers of Si-doped n-GaAs in an environmentally friendly NaCl based electrolyte, with switching the applied voltage from a high voltage to lower one and vice-versa. Switching of the applied voltage in the process of anodization was found to cause the formation of layered porous structures with different degrees of porosity. Crystallographically oriented pores shaped as triangular prisms were produced in a stationary regime of anodization, while a more complex morphology of pores was observed at the interface between the two layers with different degrees of porosity, including pores composed of three circular ones. Based on the results of the morphology study using scanning electron microscopy, a possible mechanism of the formation of such kind of pores in the dynamic transitory regime of anodizing is discussed.

Growth of high-quality epitaxy of GaAs on Si with engineered Ge buffer using MOCVD

This article presents novel process methods to grow GaAs on 200 mm Si substrates with low threading dislocation density (TDD) and no anti-phase domains (APDs). The GaAs layers were grown on the engineered Ge buffer with thickness of 0.9 and 1.7 μm with surface roughness as low as 0.58 nm. The growth temperature of GaAs was tailored from low, intermediate, and high temperature (LT, IT, and HT) at 460 °C, 600 °C, and 670 °C, respectively, to impede the defects to propagate to the HT layer. It has been demonstrated that the quality of GaAs layers is sensitive to the surface roughness and layer quality of Ge buffer. Therefore, Ge buffer was grown selectively with lateral overgrowth over the wafer to decrease the defect density to a low level as possible for GaAs growth. For all samples, Chemical mechanical polishing (CMP) was applied for Ge buffer to ensure the surface roughness prior to GaAs growth. This study presents novel methods to optimize/improve GaAs growth on engineered Ge buffer grown on 0° − and 6° − miscut Si substrates. The impact of layer quality, surface roughness, and design of Ge buffer growth (selective or non-selective growth) on GaAs growth has been studied. The outcome of this study provides a monolithic solution for photonics and electronics in large size Si substrates.

Classification of in situ reflection high energy electron diffraction images by principal component analysis

The reflection high-energy electron diffraction (RHEED) method is widely used for the in situ observation of molecular beam epitaxy (MBE). This is because the RHEED pattern dynamically changes according to the growth conditions, such as surface temperature and material supply. However, to date, the RHEED pattern has been categorized and recognized based on the experience of the researcher. In this study, we investigated the classification of RHEED pattern datasets without using labeling by the principal component analysis method that reduces the dimensionality of the data. The RHEED images were successfully classified during the MBE growth of GaAs, demonstrating that unsupervised learning can be used to recognize RHEED patterns.

Wurtzite phase control for self-assisted GaAs nanowires grown by molecular beam epitaxy

The accurate control of the crystal phase in III–V semiconductor nanowires (NWs) is an important milestone for device applications. Although cubic zinc-blende (ZB) GaAs is a well-established material in microelectronics, the controlled growth of hexagonal wurtzite (WZ) GaAs has thus far not been achieved successfully. Specifically, the prospect of growing defect-free and gold catalyst-free wurtzite GaAs would pave the way towards integration on silicon substrate and new device applications. In this article, we present a method to select and maintain the WZ crystal phase in self-assisted NWs by molecular beam epitaxy. By choosing a specific regime where the NW growth process is a self-regulated system, the main experimental parameter to select the ZB or WZ phase is the V/III flux ratio. Using an analytical growth model, we show that the V/III flux ratio can be finely tuned by changing the As flux, thus driving the system toward a stationary regime where the wetting angle of the Ga droplet can be maintained in the range of values allowing the formation of pure WZ phase. The analysis of the in situ reflection high energy electron diffraction evolution, combined with high-resolution scanning transmission electron microscopy (TEM), dark field TEM, and photoluminescence all confirm the control of an extended pure WZ segment, more than a micrometer long, obtained by molecular beam epitaxy growth of self- assisted GaAs NWs with a V/III flux ratio of 4.0. This successful controlled growth of WZ GaAs suggests potential benefits for electronics and opto-electronics applications.