1-μm-thick zinc-blende GaAs (111) films were grown by molecular-beam epitaxy on wurtzite GaN∕sapphire (0001) templates. In spite of a ∼20% lattice mismatch, epitaxial growth was realized, so that the GaAs films showed good adhesion and their surface had a larger mirror-like area with an average surface roughness of 10 nm. Transmission electron microscopy revealed a flat and abrupt epitaxial GaAs∕GaN interface with some nanocavities and a large number of dislocations. Reasonably good crystalline quality of the GaAs films was confirmed by Raman characterization. Spectroscopic ellipsometry showed sharp interference fringes and characteristic parameters in the range of 0.75–5.3 eV. Photoluminescence study revealed extended band tails and dominance of non-radiative carrier recombination.

A model is developed for the elastic stress relaxation via formation of prismatic dislocation loops in a vicinity of the As–Sb nanoclusters built in GaAs matrix. The model is based on the experimental investigation of the microstructure of the As–Sb nanoclusters, which can be produced in Sb-doped GaAs films by the molecular-beam epitaxy at low temperature and subsequent anneal. A strong anisotropic mismatch between the As–Sb nanoclusters and GaAs matrix has been revealed by transmission electron microscopy. This mismatch was proven to be a reason for the formation of nanoscale dislocation loops near the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific nonlinear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self-energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena in precipitated semiconductors.

Microstructure of GaAs films grown by molecular-beam epitaxy at low temperature and delta doped with Sb was studied by transmission electron microscopy. The material contained 0.5 at. % excess of arsenic that precipitated during post growth anneals. The Sb δ doping was found to strongly affect the microstructure of precipitates (clusters) and their ripening rate upon annealing. Segregation of Sb impurity in the clusters was revealed. In contrast to the well known pure As clusters, the As–Sb clusters induced strong local deformations in the surrounding GaAs matrix. Until a threshold diameter of 7–8 nm the clusters and surrounding matrix were coherently strained. Larger clusters were associated with dislocation loops of interstitial type. The cluster-loop orientation relationships were determined. Relaxation of local strains by formation of the dislocation loops was studied both experimentally and theoretically.

The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4–5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects.

Comparative study of excess As precipitation at Ostwald ripening stage in two-(2D) and three-dimensional (3D) cluster arrays in GaAs films grown by MBE at low-temperature (LTG GaAs) and either undoped or delta-doped with In was performed by TEM. The average cluster size in 3D arrays was monitored depending on annealing temperature, and As diffusion effective activation energy has been evaluated to be (2.0 +/- 0.2) e V. The ratios between the number and whole volume of As clusters accumulated by In delta-layer and those in the residual GaAs film bulk were observed to considerably increase with annealing temperature and GaAs film thinning, the ratios being independent on growth temperature. For annealing temperatures in the range 600-700degreesC when the cluster size reaches its appropriate 3-7 nm value the LTG GaAs layer thickness required to form complete 2D cluster array has been found to be in the range 20 to 50 nm.

Sb-doped (both uniformly and delta-doped) GaAs films were grown by molecular beam epitaxy (MBE) at low temperature (LT) and annealed in the MBE setup at various temperatures within the range of 400-850 degrees C. The annealed samples were studied using transmission electron microscopy (TEM), x-ray diffraction and near-infrared optical absorption. The arsenic antisite defect concentration in as-grown samples was found to be as high as (6 - 8) x 10(19) cm(-3). The anneal of conventional (Sb-free) LT GaAs led to precipitation of excess arsenic, so that As clusters are built in the GaAs matrix without formation any additional extended defects. In contrast to that the TEM study of annealed LT GaAs films doped with Sb revealed dislocation loops which were attached to As clusters. The loops lied in 001 planes and grow in (110) directions. Their Burgers vector was found to be perpendicular to the loop plane. Analysis of experimental results and theoretical calculations allow us to conclude that in Sb-doped Lt GaAs films the arsenic clusters are enriched by antimony and, as a result, create strong local deformations in the surrounding matrix.

As–Sb compositional intermixing was studied by transmission electron microscopy (TEM) in GaAs films grown by molecular-beam epitaxy at low temperature (LT) and δ doped with antimony. The TEM technique was calibrated by imaging the as-grown films with δ layers containing various amounts of Sb. The calibration allowed us to deduce the effective As–Sb interdiffusion coefficient from apparent thickness of the Sb δ layers in the films subjected to isochronal anneals at 400–600 °C. The As–Sb intermixing in LT GaAs was found to be much enhanced when compared to conventional material. Its temperature dependence yields a diffusion coefficient of DAs–Sb=2×10−14 exp(−0.62±0.15 eV/kt) cm2 s−1. Since the kick-out mechanism operating under equilibrium conditions is valid for As–Sb interdiffusion in GaAs, the enhanced intermixing was attributed to an oversaturation of arsenic self-interstitials in the LT GaAs films. The effective activation energy for As–Sb interdiffusion in LT GaAs seems to be reasonably close to the migration enthalpy of As interstitials, whereas their concentration was roughly estimated as 1018 cm−3.

Compositional intermixing was studied by transmission electron microscopy of low-temperature (LT) grown GaAs films delta-doped with isovalent In and Sb impurities. The diffusion was found to be enhanced on both anion and cation sublattices of LT GaAs when compared to that for conventional stoichiometric material. The phenomenon seems to be a result of high concentration of excess-arsenic-related point defects. These are gallium vacancies mediating diffusion on gallium sublattice and arsenic interstitials assisting diffusion on arsenic sublattice. The effective In-Ga and Sb-As interdiffusion coefficients and their activation energies have been determined.

Accumulation of electrons and holes has been revealed by capacitance-voltage technique in Ag-cluster containing GaAs layers sandwiched between n-type or p-type GaAs buffers. As result of the majority carrier accumulation, large depletion region forms in adjacent buffers. Simulation of the capacitance-voltage characteristics based on numerical solution of the Poisson equation showed the concentration of accumulated charge to be as high as 1x10(12) cm(-2) which is comparable with concentration of As clusters determined from transmission electron microscopy study.

Quantum dots (QDs) formed on GaAs(100) substrates by InAs deposition followed by (Al,Ga)As or (In,Ga,Al)As overgrowth demonstrate a photoluminescence (PL) peak that is redshifted (up to 1.3 μm) compared to PL emission of GaAs-covered QDs. The result is attributed to redistribution of InAs molecules in the system in favor of the QDs, stimulated by Al atoms in the cap layer. The deposition of a 1 nm thick AlAs cover layer on top of the InAs–GaAs QDs results in replacement of InAs molecules of the wetting layer by AlAs molecules, leading to a significant increase in the heights of the InAs QDs, as follows from transmission electron microscopy. This effect is directly confirmed by transmission electron microscopy indicating a transition to a Volmer–Weber-like QD arrangement. We demonstrate an injection laser based on this kind of QDs.

Structural and optical properties of InAs quantum dots (QDs) overgrown by thin (In,Ga,Al)As layers were investigated. Adding In as well as Al during overgrowth of the QDs results in an increase in QD size and a change in QD shape due to reduced of In diffusion from the QDs during overgrowth and transport of In atoms from the wetting layer. This leads to a red shift of die emission and allows to realise 1.3 mum emission using QDs in the initial stage of formation.

Low-temperature grown GaAs films with indium delta layers are studied by transmission electron microscopy. The delta layers in the as-grown film are found to be as thick as four monolayers (ML) independently of a nominal In deposit of 0.5 or 1 ML, a thickness which reflects the film surface roughness during the low-temperature growth. A pronounced In–Ga intermixing is observed in the films subjected to 500–700 °C isochronal anneals. The In–Ga interdiffusion diffusivity is evaluated. The effective activation energy for In–Ga interdiffusion is found to be 1.1±0.3 eV which is significantly smaller than a value of 1.93 eV for a stoichiometric GaAs. The difference seems to result from a loss of the gallium vacancy supersaturation upon annealing, and is consistent with an annihilation enthalpy of 0.8 eV.

Recent achievements in controlling the electronic spectrum of InAs-based quantum dots (QDs) formed by self-organization phenomena during the initial stages of strained layer epitaxy are reviewed. Three different ways to exercise this control are discussed, based on variation of QD size with the amount of QD material deposited, tuning of the electronic levels in QDs by changing the matrix bandgap, and electronic coupling of neighbouring QDs vertically stacked in the growth direction. Possibilities to prevent thermal evaporation of carriers out of QD states and to tune the emission wavelength in the range 0.85-1.3 µm on GaAs substrates and up to 2 µm on InP substrates are demonstrated.

We demonstrate the possibility of extending the spectral range of luminescence due to InAs quantum dots (QDs) in a GaAs matrix up to 1.7 μm. Realization of such a long wavelength emission is related to formation of lateral associations of QDs during InAs deposition at low substrate temperatures (∼320–400 °C).

InAs self-organized quantum dots inserted in InGaAs quantum well have been grown on GaAs substrates by molecular beam epitaxy. The lateral size of the InAs islands has been found to be approximately 1.5 times larger as compared to the InAs/GaAs case, whereas the island heights and surface densities were close in both cases. The quantum dot emission wavelength can be controllably changed from 1.1 to 1.3 μm by varying the composition of the InGaAs quantum well matrix. Photoluminescence at 1.33 μm from vertical optical microcavities containing the InAs/InGaAs quantum dot array was demonstrated.

This paper presents a comprehensive experimental, theoretical and computer simulation study of very low-energy (3–35 eV) argon ion sputtering of β-MoSi2(0001). Modification of MoSi2 surface composition under low-energy ion bombardment was studied by Auger electron spectroscopy (AES) and X-ray photoelectronic spectroscopy (XPS). The detected changes of surface composition were attributed to preferential sputtering combined with threshold effects. To verify the interpretation, an analytical theory of near-threshold sputtering of compounds is developed which provides a general relation between the sputter threshold energy of target atoms on one side and their atomic masses, surface-binding energies as well with the ion atomic mass on the other side. Elementary mechanisms of near-threshold sputtering are found from the theory and molecular dynamics simulation for MoSi2. Threshold energies for various mechanisms of Mo and Si sputtering are calculated and used to explain the experimental evidence. From results of the work it is concluded that the experimental study of surface composition changes after near-threshold sputtering provides a radically new approach to investigate surface binding in compounds.

Delta doping with antimony isovalent impurity has been employed as a precursor for two-dimensional precipitation of excess arsenic in GaAs grown by molecular-beam epitaxy at low substrate temperature (LT-GaAs), and subsequently annealed. LT-GaAs films delta doped with indium isovalent impurity showed previously to provide two-dimensional As cluster sheets were studied for comparison. Small clusters observed by transmission electron microscopy at the Sb delta layers had an unusual lens shape and, probably, nonrhombohedral microstructure. These clusters induced strong local strains in the surrounding GaAs matrix. After annealing under the same conditions, the clusters at the Sb delta layers were found to be bigger than those at the In delta layers. Additionally, nucleation of the arsenic clusters at the Sb delta layers occurs at a relatively low annealing temperature. The observed precipitation features indicate that delta doping with Sb is more effective for two-dimensional precipitation of the excess As in LT-GaAs as compared with In delta doping.

A method is proposed to increase the emission wavelength from structures grown on GaAs substrates by inserting a strained InAs quantum dot array into an external InGaAs quantum well. The dependence of the luminescence peak position on the active region design was investigated for structures grown by this method. Room-temperature photo- and electroluminescence spectra in the 1.3-mu m wavelength range are compared. (C) 1999 American Institute of Physics. [S1063-7826(99)00602-X].