Kevin H. Chang

Role of strain and growth conditions on the growth front profile of InxGa1−xAs on GaAs during the pseudomorphic growth regime

Theoretical and experimental studies are presented to understand the initial stages of growth of InGaAs on GaAs. Thermodynamic considerations show that, as strain increases, the free‐energy minimum surface of the epilayer is not atomically flat, but three‐dimensional in form. Since by altering growth conditions the strained epilayer can be grown near equilibrium or far from equilibrium, the effect of strain on growth modes can be studied. In situ reflection high‐energy electron diffraction studies are carried out to study the growth modes and surface lattice spacing before the onset of dislocations. The surface lattice constant does not change abruptly from that of the substrate to that of the epilayer at the critical thickness, but changes monotonically. These observations are consistent with the simple thermodynamic considerations presented.

Characteristics of dislocations at strained heteroepitaxial InGaAs/GaAs interfaces

The formation, interaction, and propagation of misfit dislocations in molecular‐beam epitaxial InGaAs/GaAs heterointerfaces have been studied by transmission electron microscopy. With the lattice mismatch less than 2%, most of the interfacial dislocations are found to be 60° mixed dislocations introduced by glide processes. Sessile edge‐type dislocations can also originate from the combination of two 60° mixed dislocations. The ratio of densities of edge dislocations to 60° dislocations was increased during the later part of the elastic strain relaxation. These sessile edge dislocations may be generated in appreciable numbers through a climb process. For large lattice‐mismatched systems, the majority of the misfit dislocations are pure edge dislocations and high threading dislocation density is generally found. The interfacial dislocation network is found to contain regions of dislocations with the same Burgers vector that extend over several micrometers. The results support a mechanism that involves misf...

Crosshatched surface morphology in strained III-V semiconductor films

The correlation between the surface crosshatched morphology and the interfacial misfit dislocations in strained III‐V semiconductor heteroepitaxy has been studied. The surface pattern is clearly seen on samples grown at high temperature (520 °C) and those with small lattice‐mismatched (f<2%) systems. A poorly defined crosshatched morphology was found on layers grown at relatively low temperature (400 °C). As the lattice mismatch of the strained layer becomes larger than 2%, a roughly textured surface morphology is commonly observed in place of actual cross‐hatching. Few threading dislocations are observed in the strained layer when the crosshatched pattern develops. It is also noted that the surface crosshatched pattern develops after the majority of the interfacial misfit dislocations are generated. The result suggests that the surface crosshatch pattern is directly related to the generation of interfacial misfit dislocations through glide processes.

A study of strain‐related effects in the molecular‐beam epitaxy growth of InxGa1−xAs on GaAs using reflection high‐energy electron diffraction

In this paper we examine the role of strain in the molecular‐beam epitaxy (MBE) growth process by studying growth in InxGa1−xAs on GaAs with x varying from 0 to 0.5. This range covers the critical thickness regime for dislocation formation from ∞ to 12 monolayers. We have studied MBE growth for both on‐axis (100) and misoriented substrates. The first issue we address in this paper is the role of strain in controlling the atomic‐surface migration. We find from reflection high‐energy electron diffraction (RHEED) studies during growth of InxGa1−xAs that as x is increased, the surface migration decreases rapidly. The growth front of the growing structure roughens due to this decreased migration and we have studied the recovery time for the growth front to smoothen. The surface recovery time increases rapidly as the strain in the system increases. Conversely, when GaAs growth is resumed, there is a recovery of the RHEED average intensity and oscillations (peak to peak). At higher growth temperatures, layer‐by‐...

Lattice‐mismatched In0.53Ga0.47As/In0.52Al0.48As modulation‐doped field‐effect transistors on GaAs: Molecular‐beam epitaxial growth and device performance

We describe here the properties of In0.53Ga0.47As/In0.52Al0.48As modulation‐doped heterostructures and field‐effect transistors grown directly by molecular‐beam epitaxy on GaAs substrates. The generation and nature of dislocations in the films have been studied by transmission‐electron microscopy. The final heterostructure contains a series of compositional steps of InxGa1−xAs (0≤x≤0.53) to generate and control the dislocation movement. The modulation‐doped heterostructures are characterized by μ300 K=8 150 cm2/V s (ns=2.7×1012 cm−2) and μ20 K=26 100 cm2/V s (ns=2.1×1012 cm−2) which compare very favorably with values measured in similar lattice‐matched heterostructures on InP. 1.4‐μm gate‐modulation‐doped field‐effect transistors exhibit gm(ext)=240 mS/mm and fT=21 GHz. The drain current variation with gate bias is linear and the transconductance is uniform over a sizeable voltage range. These material and device characteristics indicate that InxGa1−xAs/InxAl1−xAs transistors (with x varying over a certai...

Transmission electron microscopy of strained InyGa1−yAs/GaAs multiquantum wells: The generation of misfit dislocations

We have investigated the generation and propagation of misfit dislocations in strained InyGa1−yAs/GaAs multiquantum wells grown by molecular‐beam epitaxy, with cross‐sectional transmission electron microscopy. The samples are of excellent optical quality, with multiquantum wells having well widths of 100 A, being characterized by excitonic linewidths and Stokes shifts of 1.5–2.5 and 1–2 meV, respectively. We have examined the growth of 2‐μm‐thick multiquantum‐well samples grown either directly on GaAs, or with an intermediate composition buffer layer, and for the cases of small (y=0.07) and large (y=0.16) misfits. It is seen that for the case of quantum wells with small misfit, grown directly on GaAs, metastable growth can be achieved. This is confirmed by low‐temperature absorption measurements and from transmission electron microscopy experiments performed both before and after post‐growth thermal annealing. In the case of quantum wells with large misfits directly grown on GaAs, dislocations are generat...

Molecular beam epitaxial growth and luminescence of InxGa1−xAs/InxAl1−xAs multiquantum wells on GaAs

This letter reports the successful molecular beam epitaxial growth of high‐quality InxGa1−xAs/InxAl1−xAs directly on GaAs. In situ observation of dynamic high‐energy electron diffraction oscillations during growth of InxGa1−xAs on GaAs indicates that the average cation migration rates are reduced due to the surface strain. By raising the growth temperature to enhance the migration rate and by using misoriented epitaxy to limit the propagation of threading and screw dislocations, we have grown device‐quality In0.15Ga0.85As/In0.15Al0.85As multiquantum wells on GaAs with a 0.5–1.0 μm In0.15Ga0.85As buffer layer. The luminescence efficiency of the bound exciton peak increases with misorientation and its linewidth varies from 11 to 15 meV.

Epitaxial growth and characterization of GaAs/Al/GaAs heterostructures

Abstract We report on transmission electron microscopy, secondary ion mass spectroscopy, X-ray and Raman scattering studies of GaAs/Al/GaAs heterostructures grown by migration enhanced epitaxy.

Optical and structural properties of molecular-beam epitaxial GaAs on sapphire

We have evaluated the structural and optical properties of GaAs grown by molecular‐beam epitaxy on (0001) and (0112)‐oriented sapphire substrates for possible direct deposition on sapphire optical fibers and optoelectronic device applications. X‐ray diffraction studies and cross‐sectional transmission electron microscopy measurements show that the GaAs films are single‐crystal and have a (111) orientation for both substrate orientations. Both x‐ray and temperature‐dependent photoluminescence measurements indicate that the quality of the GaAs films is better for the (0112) sapphire orientation. The best results are produced when growth is initiated at a very slow rate (∼0.1 μm/h) and low temperature (∼400 °C) followed by growth parameters for normal homoepitaxial GaAs (1 μm/h, 560–600 °C). The incorporation of a graded band gap strained layer in InGaAs/GaAs superlattice near the sapphire–GaAs interface also improves the optical quality of the GaAs films. Low‐temperature photoluminescence spectra is domin...

Growth phenomena and characteristics of strained InxGa1-xAs on GaAs

Abstract We have investigated the molecular beam epitaxial growth, structural and optical properties of InGaAs on GaAs. We have focused first on the initial stages of growth where the growth is expected to be under coherent strain and second on the nature of single and multiple quantum well heterointerfaces.