Epi-ready Substrates Research Articles

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

We demonstrate the growth of GaAs solar cells by hydride vapor phase epitaxy (HVPE) on epi-ready and previously spalled (110) GaAs wafers as an advance towards a potentially low-cost (110)-based device platform. Controlled spalling offers a fracture-based path to substrate cost amortization, enabling device exfoliation and substrate reuse, but the faceted surface generated during the spalling of (100)-oriented GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110) substrates instead eliminates faceting by aligning the substrate surface with the predominant crystal cleavage plane. III–V epitaxy of solar cells is significantly less developed on (110)-oriented substrates, however. Here, we develop (110)-based GaAs solar cells grown by HVPE on epi-ready substrates, demonstrating equal performance to devices grown on the more standard (100) orientation. We also characterize the surface of spalled, (110)-oriented substrates, revealing flat terraces separated by steps with sub-micron-scale height on average. Finally, we present an initial device grown on a previously spalled surface without additional surface re-preparation with nearly 16% efficiency under a simulated AM1.5G spectrum. Together, these results provide preliminary evidence of a potentially low-cost path to enable terrestrial III–V photovoltaics via the (110) substrate orientation.

GaN-based heterostructures with CVD diamond heat sinks: A new fabrication approach towards efficient electronic devices

A new approach to the fabrication of efficient heat sinks for GaN-based transistors is demonstrated. A key feature of this work is the growth of polycrystalline diamond coating on the functional silicon layer of SOI wafers followed by etching of a thick silicon substrate and a thin thermal oxide. As a result, composite epi–ready substrates consisting of a thin (410 nm) monocrystalline silicon functional layer on top of the 150 µm-thick polycrystalline diamond heat sink were fabricated. GaN heterostructures were grown on top of the silicon layer, which resulted in an effective thermal contact between CVD diamond and GaN structure. The packaged ungated transistors were made to analyze the efficiency of the developed heat sink. Improved heat removal structures showed the decrease in surface temperature by more than 50 °C at base temperature of Tb=85 °C and dissipation power of Pdiss=6.9 W/mm compared to conventional GaN-on-SiC technology and by more than 20 °C at Tb=25 °C, Pdiss=6.9 W/mm compared to up-to-date GaN-on-Diamond equivalent transistors reported by other groups. New substrate fabrication technology positively impacts GaN-based device output characteristics and reliability, which is important in improving communication systems, radars, and secondary power supply systems.

Using electron channeling contrast imaging to inform and improve the growth of high-efficiency GaAs solar cells on nanopatterned GaAs substrates

Patterned substrates provide opportunities for reducing the cost of high-efficiency III-V devices by incorporating mechanically weak layers beneficial for substrate reuse (e.g. by spalling). In this work, the functionality of electron channeling contrast imaging (ECCI) as a tool to efficiently understand and mitigate defect formation is exemplified by developing a process in which high-quality III-V material can be grown on nanopatterned GaAs substrates. Reactive ion etching used in the patterning process was found to damage the GaAs substrate surface, leading to the formation of stacking faults in the epitaxial material as observed by ECCI. Etching the patterned substrates in a 1 NH4OH: 1 H2O2: 50 DI H2O solution for 10 s prior to growth removed the substrate surface damage and stacking faults were no longer present. Growth of solar cell device structures initially produced samples with many macroscale flaws creating shunts in the devices, which complicated the assessment of material quality by device measurements. However, ECCI revealed that the epitaxial material surrounding macroscale flaws was free from any crystallographic defects such as stacking faults and threading dislocations. With this knowledge, we focused on refining the patterning process to eliminate the macroscale flaws. Solar cells were then grown on the improved nanopatterned substrates and exhibited device structures with defect densities less than 5 × 105 cm−2 and average conversion efficiency of 24.8%, nearly identical to devices grown on unpatterned epi-ready substrates (25.0%).

4H-SiC Epi-Ready Substrate Qualification by Using Mirror Electron Microscope Inspection System

Crystal damage beneath the surface remaining after chemo-mechanical polishing (CMP) and basal plane dislocations (BPDs) of 4H-SiC epi-ready substrates have been inspected by using a mirror electron microscope inspection system non-destructively. Distributions of crystal damage and BPDs as well as their average densities are estimated by acquiring 80-μm square mirror electron images at positions distributed with an equal pitch over a substrate (“Discrete point set inspection”). Although the total inspected area is less than 1% of the entire substrate area, the inspection results for nine commercially available wafers reveal that there are large differences in surface polishing quality and BPD density between them. Evaluation on an epitaxial layer with a thickness of 10 μm grown on one of the inspected substrates indicated that correlation between distribution of the crystal damages on the substrate and that of bunched steps on the epitaxial layer surface.

Assessing epitaxial regrowth material quality on a micro-transfer printed GaAs substrate

Micro-transfer printing has demonstrated value for device- and array-level heterogeneous integration in a variety of applications. Here, it is used instead to assemble unique substrates with the potential to enable III–V growth templates that are both low-cost and specified at any desired lattice parameter within the range of III–V materials. Critical to this, epitaxial growth crystal quality must be established as comparable to that produced on conventional epi-ready substrates. We demonstrate epitaxial regrowth on gallium arsenide membranes that were transfer printed from their source substrate and onto a target handle. Both morphology and luminescence properties were characterized. Comparing the transfer printed membrane epitaxy with epitaxy on a conventional substrate, we found recombination rates and spatial uniformity from power-dependent photoluminescence and cathodoluminescence, respectively, to yield similar results, suggesting material quality was not adversely limited by the engineered substrate.

III–V Solar Cells Grown on Unpolished and Reusable Spalled Ge Substrates

Substrate reuse offers a promising route toward enabling high-efficiency III–V solar cells to become cost-competitive for one-sun terrestrial applications. In this study, Ge films were spalled using an electroplated Ni stressor layer, and the fracture surface was characterized. Initial heteroepitaxial GaAs films grown on spalled Ge substrates by hydride vapor phase epitaxy were found to be single crystal with nearly equivalent growth rates between growth on epi-ready and unpolished spalled Ge substrates. We show the first demonstration of III–V solar cells (GaInAsP, Eg ∼ 1.7 eV) grown on unpolished spalled Ge substrates to assess the viability of substrate reuse. We demonstrate equivalent performance for a solar cell grown on spalled Ge and on a coloaded epi-ready Ge substrate, despite the residual roughness on the spalled Ge substrate and the lack of any substrate surface preparation. This initial demonstration of combining substrate reuse with the ability to grow III–V solar cells using a high growth rate and high throughput deposition process is a promising step toward low-cost III–V photovoltaics.

Optimization of conditions for thermal smoothing GaAs surfaces

GaAs thermal smoothing by annealing in conditions which are close to equilibrium between the surface and vapors of As and Ga was earlier proved to be effective for the step-terraced surface formation on epi-ready substrates with a small root-mean-square roughness (Rq ≤ 0.15 nm). In the present study, this technique is further developed in order to reduce the annealing duration and to smooth GaAs samples with a larger initial roughness. To this end, we proposed a two-stage anneal with the first high-temperature stage aimed at smoothing "coarse" relief features and the second stage focused on "fine" smoothing at a lower temperature. The optimal temperatures and durations of two-stage annealing are found by Monte Carlo simulations and adjusted after experimentation. It is proved that the temperature and duration of the first high-temperature stage are restricted by the surface roughening, which occurs due to deviations from equilibrium conditions.

(Invited) Progress and Challenges of AlGaN Schottky Diodes Grown on AlN Substrates

Lateral and vertical power switching devices being intensively developed in GaN and SiC materials are beginning to reach a state of maturity and to displace traditional Si devices in certain applications. The relative advantage of these wide bandgap materials, which stems from intrinsic materials properties, can be compared in terms of an applicable figure of merit (FOM), indicating theoretical limits [1]. The most commonly discussed FOM for power applications is the unipolar FOM [2], based on reduction of conduction losses in the on-state and high voltage blocking in the off-state of vertical devices, VB 2/Ron,sp = εμnEc 3/4, where VB is the off-state avalanche breakdown voltage, Ron,sp is the specific on-state resistance, ε is the semiconductor permittivity, μn is the electron mobility, and Ec is the critical electric field. The unipolar FOM scales as the cube of Ec , which is itself a strong function of the bandgap [3], leading to the key advantage for wide bandgap materials. Possessing bandgaps wider than GaN (3.4 eV), AlGaN alloys are expected to provide improved performance. We have investigated quasi-vertical Schottky barrier diodes, consisting of nominal Al0.8Ga0.2N drift layers grown on high quality AlN single crystal substrates. HexaTech has developed proprietary seeded AlN crystal growth technology based on physical vapor transport (PVT), allowing iterative expansion of single crystal size, while maintaining low dislocation density (<103 cm-2), as determined by x-ray diffraction and defect-selective etching. AlN boules were oriented, sliced, lapped, and chemo-mechanically polished (CMP) to produce epi-ready c-plane substrates. Due to the highly insulating nature of the Al-face AlN substrates (resistivity >1013 Ωcm at room temperature), quasi-vertical Schottky diode structures were grown by metal-organic chemical vapor deposition (MOCVD). The device structure consisted of an AlN homoepitaxial layer, followed by a 0.6 µm thick pseudomorphic Si-doped Al0.8Ga0.2N contact layer ([Si] ~2x1019 cm-3), a 1 µm thick low-doped Al0.8Ga0.2N drift layer, and a 0.3 µm Mg-doped AlN cap layer ([Mg] ~2x1018 cm-3), serving as a junction termination extension (JTE). Despite the high activation energy of the Mg dopant in AlN, the Mg acceptors are expected to be ionized under high reverse bias, due to the strong band bending. Following epitaxial growth and dopant activation, circular device mesas were defined by dry etching down to the n-AlGaN contact layer, the JTE region atop the mesa was defined into a series of lateral steps and the Schottky contact area was etched down to the drift layer, Ohmic contacts were deposited and annealed, circular Schottky contacts were deposited, and a blanket polyimide passivation layer was deposited and patterned. Schottky diodes with diameters ranging from 0.3 to 1.0 mm were fabricated. Capacitance-voltage measurements were used to determine the free carrier concentration of the drift region, 2.0x1017 cm-3. The forward and reverse current-voltage characteristics were measured as a function of temperature. The specific on-state resistance was 125 mΩcm2 at room temperature and 190 mΩcm2 at 150 °C, which is partly attributed to high contact resistance. Diodes exhibited a current rectification ratio of ~106. The off-state breakdown voltage was up to 500 V. Breakdown tended to be destructive, likely limited by the polyimide passivation, suggesting improved blocking performance could be achieved with a better dielectric and more developed edge termination strategy. Field calculations based on the measured carrier concentration and breakdown voltage indicated a trapezoidal electric field in the drift region with a 7 MV/cm field at the Schottky junction. This talk will review growth and expansion of high quality AlN single crystals by PVT, and fabrication of epi-ready AlN substrates. Results for high Al composition Schottky diodes grown on these substrates will be presented. Challenges for this emerging technology, including doping limitations and compensation in AlGaN alloys, Ohmic contacts, and device termination will be discussed. [1] T. P. Chow, I. Omura, M. Higashiwaki, H. Kawarada, and V. Pala, IEEE Trans. Electron Devices, 64, 856 (2017). [2] K. Shenai, R. S. Scott, and B. J. Baliga, IEEE Trans. Electron Devices, 36, 1811 (1989). [3] J. L. Hudgins, G. S. Simin, E. Santi, and M. A. Khan, IEEE Trans. Power Electron., 18, 907 (2003).

Investigation of hillocks formation on (1 0 0) HgCdTe layers grown by MOCVD on GaAs epi-ready substrates

In this paper we present the recent progress in the growth of (100) HgCdTe epilayers using metal organic chemical vapour deposition on GaAs epi-ready substrates. Particular progress has been achieved in the reduction of macro-defects known as “hillocks”, revealed on the surface of HgCdTe epilayers with (100) crystallographic orientation. The large-scale defects can arise from such sources as poor substrate processing, dust and remnants from previous deposition, and non optimal parameters of nucleation and growth process. In our experiment, hillocks density was decreased to <102cm−2 by proper choice of the growth parameters.Obtained epilayers are suitable for device fabrication. So far, significant improvements has been obtained in photoconductors operated at near-room temperatures. Devices fabricated from (100) HgCdTe have about one order of magnitude higher voltage responsivity than their (111) B counterparts.

Recent Developments in Mercury Cadmium Telluride IR Detector Technology

In spite of many attempts to find better material for Infrared Detectors, the II-VI compound HgCdTe still dominates the high performance end of the market. Since its invention in 1959, HgCdTe technology evolved from bulk crystal growth and crude single infrared detectors to very sophisticated, epitaxially grown material and large format IR imaging arrays of photovoltaic devices. Today, the applications driven research and development in this field are directed towards high pixel density beyond diffraction limit, high yield, reduced cooling and multiband and hyperspectral operation. In order to meet these goals there is an urgent need for still better quality HgCdTe material and new band engineered devices with reduced dark current and noise levels. In terms of HgCdTe material, the most challenging is development of large area, high quality epi-ready substrates allowing for growth of HgCdTe with low dislocation defect density – a major source of dark current and noise. Traditionally, lattice matched CdZnTe with 4% Zn content has been used. However, the cost of CdZnTe substrates is prohibitive, their size is limited, and hence not adequate for today’s large size detector arrays. The readily available large size Si and GaAs substrates have been investigated for some time but due to large lattice mismatch (19% and 14.3% respectively) few microns thick buffer layers of CdTe are needed to reduce the high lattice dislocations density in HgCdTe layers. But even with these CdTe buffer layers the best reported dislocation density in HgCdTe is still about two orders of magnitude higher than in HgCdTe epi-layers grown directly on lattice matched CdZnTe. Recently low-doped large epi-ready GaSb substrates become available and have been investigated as an alternative for HgCdTe growth. With relatively low lattice mismatch of only 6.1%, these substrates require much thinner buffer layer, and, as our studies indicate, even un-optimised growth results with CdTe buffer layer quality matching the best reported results for CdTe buffers grown on GaAs, consequently leaving much room for improvement. In parallel with development of substrates a large effort is directed towards new detector device structures with the main goals focused on reduction of dark current and noise levels, as well as simplified processing leading to higher yield. In recent years so called barrier structures attracted much attention within HgCdTe research community. The concept based on the device consisting of the n-type absorber, undoped barrier, and thin n-type contact (nBn) comes from III-V technology where it was successfully implemented in InAs/GaSb system. Theoretically device like this does not have built in voltage region (reduced dark current and noise) and if externally biased allows for a free flow of minority photo-electrons while blocking majority photo-holes. Implementation of this concept in HgCdTe material system is not straightforward as its band structure is less favourable than that of InAs/GaSb system resulting in a small barrier in the valence band as well. However, this undesirable effect may be compensated by superior HgCdTe electron mobility and photo-generated carrier lifetime. Moreover, few promising concepts for elimination of the valence band barrier in HgCdTe nBn structure have been proposed. They are based on simultaneous modulation of material composition and doping within the barrier, or alternatively, the growth of the HgTe/CdTe superlattice barrier with energy structure optimised by band engineering.

Surface properties of annealed semiconducting β-Ga2O3 (1 0 0) single crystals for epitaxy

We present a detailed study on the surface properties of conductive β-Ga2O3 (100) single-crystal epiready substrates by means of photoelectron emission spectroscopy. The surface properties are studied prior and after annealing in ultra-high vacuum (UHV). We find that untreated substrates contain a significant amount of adsorbed carbon contaminations at the surface, which can be partly removed by annealing at 800°C in UHV. Valence band photoemission evidences an upward band bending of about 0.5eV that increases with annealing, revealing the presence of an electron depletion layer at the near-surface region responsible for the insulating behavior commonly observed for semiconductive β-Ga2O3 single crystals. Our findings become crucial for epitaxial growth, as it is known that carbon modifies the electrical and structural properties of subsequent epitaxial layers.

Atomic force microscopy of partially polished and epi-ready c-plane GaN substrates obtained by an ammonothermal method

In this paper, the propagation of scratches on the surfaces of c-plane GaN substrates due to slicing and polishing is studied through atomic force microscopy (AFM). For epi-ready substrates, the AFM images confirm a flat surface with atomic step roughness, while for partially polished GaN substrates, many scratches are visible in the AFM images. A Fourier analysis of the AFM images shows that the scratches propagate more easily along the {m-plane} and {a-plane} directions on a c-plane GaN surface. Most of these scratches are generated by the mechanical slicing of GaN crystals and/or non-optimal polishing conditions. A proper chemomechanical polishing process is able to remove the damaged material and obtain a flat surface with atomic step roughness. This observation is evidence for the anisotropy of mechanical properties of GaN crystals in the microscale range.

Low temperature oxide desorption in GaAs (111)A substrates

The aim of this work is to study oxide removal processes on GaAs (111) A substrates previous to epitaxial growth. We have studied conventional thermal desorption and processes based on the reduction of surface oxides by deposition of gallium, indium and exposure to atomic hydrogen.We have determined substrate temperatures (Ts) for optimum oxide removal in epi-ready substrates by the different studied processes: Ts=540°C for thermal desorption, Ts=505°C for indium deposition and Ts=400°C for oxide desorption by exposure to atomic hydrogen. All these processes allow for a subsequent good quality epitaxial growth. These results cannot be directly extended to oxide removal in grown samples that have been exposed to air outside the growth chamber. In this case, we have found that only indium deposition and exposure to atomic hydrogen are compatible with regrowth processes.

Crack-free III-nitride structures (&gt; 3.5 μm) on silicon

ABSTRACTIII-nitride structures on Si are of great technological importance due to the availability of large area, epi ready Si substrates and the ability to heterointegrate with mature silicon micro and nanoelectronics. High voltage, high power density, and high frequency attributes of GaN make the III-N on Si platform the most promising technology for next-generation power devices. However, the large lattice and thermal mismatch between GaN and Si (111) introduces a large density of dislocations and cracks in the epilayer. Cracking occurs along three equivalent {1−100} planes which limits the useable device area. Hence, efforts to obtain crack-free GaN on Si have been put forth with the most commonly reported technique being the insertion of low temperature (LT) AlN interlayers. However, these layers tend to further degrade the quality of the devices due to the poor quality of films grown at a lower temperature using metal organic chemical vapor deposition (MOCVD). Our substrate engineering technique shows a considerable improvement in the quality of 2 μm thick GaN on Si (111), with a simultaneous decrease in dislocations and cracks. Dislocation reduction by an order of magnitude and crack separation of &gt; 1 mm has been achieved. Here we combine our method with step-graded AlGaN layers and LT AlN interlayers to obtain crack-free structures greater than 3.5 μm on 2” Si (111) substrates. A comparison of these film stacks before and after substrate engineering is done using atomic force microscopy (AFM) and optical microscopy. High electron mobility transistor (HEMT) devices developed on a systematic set of samples are tested to understand the effects of our technique in combination with crack reduction techniques. Although there is degradation in the quality upon the insertion of LT AlN interlayers, this degradation is less prominent in the stack grown on the engineered substrates. Also, this methodology enables a crack-free surface with the capability of growing thicker layers.

Substrates Grown from the Vapor for ZnO Homoepitaxy

The novel method of preparation of epi-ready ZnO substrates is demonstrated. The substrates were made of unique ZnO crystals grown by chemical vapor transport method using hydrogen as the transport agent. The efiect of low-level doping (Mn, Co, Cu, and V) on the structural quality of the crystals was investigated. Atomic layer deposition was used to verify usability of the substrates for homoepitaxy. The thermal annealing prior to the atomic layer deposition process and efiect of thermal annealing of the epitaxial layers was studied. The X-ray difiraction and atomic force microscopy methods were applied to study the structural quality of the ZnO layers. Detection of the dopants in the substrates by secondary ion mass spectroscopy made possible the measurement of the thickness of the layers. The obtained root mean square roughness for both the substrates and layers ranged between 0.2 nm and 5 nm, and was dependent on the sample crystallographic orientation and sequence of polishing and annealing procedures. The optimal recipe for the epi-ready substrate preparation was formulated.

Analysis of germanium epiready wafers for III–V heteroepitaxy

Frequently, when growing III–V semiconductors on germanium substrates, unexpected differences between nominally identical substrates are encountered. Using atomic force microscopy (AFM), we have analysed a set of germanium substrates sharing the same specifications. The substrates come from the same vendor but different results come about in terms of the morphology of the epilayers produced by the same epitaxial routine (i.e. substrate W1 produced epilayers with good morphology while substrate WX produced epilayers with defects). The morphological analysis has been carried out on (a) epiready substrates; (b) samples after a high-temperature bake at 700 °C; and (c) on the samples after a hydride (PH 3) annealing at 640 °C. In the two first stages all substrates (both W1 and WX) show the same good morphology with RMS roughness below 3 Å in all cases. It is in the third stage (annealing in PH 3) that the morphology degrades and the differences between the samples become apparent. After phosphine exposure at 640 °C, the RMS roughness of both substrates approximately doubles, and their surface appears as full of peaks and valleys on the nanometre scale. Despite the general appearance of the samples being similar, a careful analysis of their surface reveals that the substrates that produce bad morphologies ( WX) show higher peaks, and some of their roughness parameters, namely, surface kurtosis and the surface skewness, are considerably degraded.

InGaAs Solar Cells Grown on Wafer-Bonded InP/Si Epitaxial Templates

AbstractInP/Si engineered substrates formed by wafer bonding and layer transfer have the potential to significantly reduce the cost and weight of III-V compound semiconductor solar cells. InP/Si substrates were prepared by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. Following thinning to remove damage caused by the implantation and exfoliation from the surface of the InP transferred film, InGaAs solar cells lattice-matched to bulk InP were grown on those substrates using metal-organic chemical vapor deposition. The photovoltaic current-voltage characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, thus providing an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.

Chemical polishing of CdZnTe substrates fabricated from crystals grown by the vertical-gradient freezing method

Chemical polishing is a process of crucial importance in the manufacture of epiready substrates for molecular beam epitaxy (MBE) of high-quality HgCdTe layers. With the aim of fabrication of (211) CdZnTe substrates, we focused on the fundamental research of polishing processes with respect to reducing subsurface damage. Wafers of the orientation (211) were prepared from the as-grown crystals by a process flow including oriented slicing, several steps of mechanical polishing, and finally chemical polishing. In the prechemical polishing process, several free and bound abrasives were applied to reach the surface roughness close to 1 nm. The surface polishing treatment included testing of the surface quality after each polishing step. We used an interferometer profiler, which yields detailed surface maps. Within chemical polishing processing, we have looked for an optimum composition of etchant based on the bromine-methanol/ethylene glycol solution and adequate polishing pad. We studied the substrate surface quality dependence on the rotation speed of the plate, sample loading weights, and duration of polishing. Correlation between the final surface roughness and layer thickness removed was established. The chemical polishing with a very low concentration of Br-methanol/ethylene glycol solution was found to yield very good CdZnTe surfaces with a perfect flatness.

Studies of oxide desorption from GaAs substrates via Ga2O3 to Ga2O conversion by exposure to Ga flux

Removal of the native oxide from GaAs wafers in the process of thermal desorption in the presence of As flux causes very significant surface degradation. We examine the merits of an alternative oxide desorption method that consists in a standard thermal oxide removal procedure preceded by a partial oxide removal at lower temperatures via conversion of the stable Ga2O3 surface oxide into a volatile Ga2O oxide by a pulsed supply of Ga in the absence of As flux. We find that a reduction of the substrate roughness by more than one order of magnitude is obtained on most epi-ready GaAs substrates regardless of their age, even if only 70% of the original gallium oxide is removed with Ga pulses, and that nearly atomically smooth surfaces are obtained with 90% oxide removal. In addition, we demonstrate that the Ga-induced oxide removal process is laterally inhomogeneous, making this method vulnerable to the accumulation of Ga droplets on the GaAs surface when more than about 90% of the surface oxide is removed. The Ga2O desorption pattern monitored with quadrupole mass spectrometry indicates that other nonvolatile species initially present on the top of the gallium oxide are also converted to a volatile species by Ga exposure before large areas of Ga2O3 become exposed. We examine the residual surface contamination left at the substrate–epilayer interface and find no significant influence of the age of the substrate, or the oxide removal method, on the measured levels of silicon, oxygen, and carbon.

Effects of buffer layer thickness and film compositional grading on strain relaxation kinetics in InAs/GaAs(111)A heteroepitaxy

The effects on the strain relaxation kinetics of a thin buffer layer's mechanical response and of the epitaxial film compositional grading are investigated in the epitaxial growth of InAs on GaAs(111)A. Two heteroepitaxial systems are analyzed, consisting of thin and thick GaAs buffer layers grown on GaAs(111)A epi-ready substrates. In both cases, one monolayer of In 0.50Ga 0.50As is grown initially on the buffer layer followed by growth of several monolayers of InAs. In both systems, strain relaxation in the grown film is measured as a function of film thickness. The experimental measurements are described successfully by a phenomenological mean-field theoretical analysis. Our results support that the mechanical response of a thin buffer layer is similar to that of a thin compliant substrate that is unconstrained at its base. Furthermore, our results indicate that the mechanical behavior of a thin buffer layer can be used in conjunction with film compositional grading toward strain relaxation engineering in semiconductor heteroepitaxy.