Following a study of implantation enhanced interdiffusion of InGaAs∕InP multiple quantum well (MQW) structures by cross-sectional scanning tunneling microscopy (XSTM), the techniques of low temperature photoluminescence spectroscopy, high-resolution x-ray diffraction (HRXRD), and grazing incidence x-ray analysis (GIXA) are used to independently investigate the suitability of a square well model for the interdiffused MQW profiles, and the observed dependence of strain development as a function of the implanted ion range relative to the MQW stacks. In agreement with previous XSTM findings, when ions are implanted through the MQWs, HRXRD measurements indicate equivalent extents of interdiffusion occurring on both sublattices, while GIXA measurements further indicate the compositional profiles to be non-Fickian and compatible with uniformly broadened square well distributions. Following shallow ion implants (where ions are deposited between the MQWs and the sample surface), (004) HRXRD measurements indicate preferential group V interdiffusion. Dynamical simulations of the superlattice envelope in the (004) HRXRD rocking curves show the compositional profiles to be non-Fickian and compatible with a square well model for the broadened compositional profiles. Additional analysis of the (001) bilayer spacing from previously published XSTM linescan data for this structure is also consistent with this finding. Results of a preliminary photoluminescence and HRXRD investigation of disordering induced by indium implants and the effects of extended annealing on a series of MQW samples (with and without implantation) are presented. Implications for the implantation enhancement of interdiffusion in the InGaAs∕InP material system are discussed. The interpretation of quantum well interdiffusion experiments in this material system in terms of Fickian diffusion models warrants revision in light of the present findings.

Scanning tunneling microscope images of lattice-matched InGaAs/InP structures were investigated using autocorrelation analysis. Correlation lengths and correlation amplitudes were calculated from constant–current empty-state images. Theoretical STM images were calculated from a model which only considered surface displacements due to strain relaxation. By comparing model and experimental correlation lengths and amplitudes it is concluded that contrast variations in constant–current images are dominated by strain relaxation effects. Changes in probe tip geometry and applications of this technique to study clustering in III–V alloys are also discussed.

Employing density-functional theory in combination with scanning tunneling microscopy, we demonstrate that a thin metallic film on a semiconductor surface may open an efficient and hitherto not expected diffusion channel for lateral adatom transport: adatoms may prefer diffusion within this metallic layer rather than on top of the surface. Based on this concept, we interpret recent experiments: We explain why and when In acts as a surfactant on GaN surfaces, why Ga acts as an autosurfactant, and how this mechanism can be used to optimize group-III nitride growth.

InGaN alloys with (0001) or (000 ) polarities are grown by plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy images, interpreted using first-principles theoretical calculations, show that there is strong indium surface segregation on InGaN for both (0001) and (000 ) polarities. Evidence for the existence and stability of a structure containing two adlayers of indium on the In-rich InGaN(0001) surface is presented. The dependence on growth temperature and group III/V ratio of indium incorporation in InGaN is reported, and a model based on indium surface segregation is proposed to explain the observations.

The surface structures and growth kinetics of InGaN(0001) are studied. It is well known that during molecular beam epitaxy GaN surfaces undergo a smooth to rough transition when the growth condition is switched from Ga rich to N rich. It is found here that indium atoms have only a small effect on this transition when deposited on GaN(0001̄), but when deposited on GaN(0001) the indium acts as a surfactant and greatly extends the regime of smooth growth. Near the smooth/rough transition of InGaN(0001) growth, a bright ∛×∛ reconstruction is observed at growth temperature. The formation kinetics of this reconstruction are studied in detail. Scanning tunneling microscopy and total energy computations are used to study the structure of InGaN(0001) surfaces under metal rich conditions. Indium is found to occupy the top two atomic layers of the crystal; its incorporation in the second layer produces significant strain, leading to the formation of small pits on the surface and increased indium concentration inside and around the pits.

The reconstruction and growth kinetics of gallium nitride (0001) and (000 (1) over bar) surfaces are studied using scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED). Results for bare GaN surfaces are summarized, with particular attention paid to the "pseudo-1 x 1" reconstruction of the (0001) face. Changes in the surface structure and kinetic processes due to indium co-deposition during growth are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

Quantum well intermixing can be accomplished via the introduction of excess defects. We review key concepts and parameters required in order to understand the physics of the technique. We show that in the cases of ion implantation and low temperature (LT) epitaxy in InP, the intermixing-causing defect is highly mobile. In both cases the interdiffusion of the group-V sublattice is greater than the group-III sublattice, resulting in strain development and a reduced splitting between the heavy hole and light hole transitions. Using additional characterization of LT InP, we propose that the mobile defect is a P interstitial

The reconstruction and surface morphology of gallium nitride (0001) and [Formula: see text] surfaces are studied using scanning probe microscopy and reflection high energy electron diffraction. Results for bare GaN surfaces are summarized, and changes in the surface structure and morphology due to codeposition of indium or magnesium during growth are discussed.

Cross-sectional scanning tunneling microscopy is used to study InGaAs/InP quantum-well intermixing produced by phosphorus implantation. When phosphorus ions are implanted in a cap layer in front of the quantum wells (in contrast to earlier work involving implantation through the wells), clear strain development is observed at the interfaces between quantum well and barrier layers after annealing. This is interpreted in terms of enhanced group-V compared to group-III interdiffusion.

Cross-sectional scanning tunneling microscopy (STM) is used to study lattice matched InGaAs/InP quantum well (QW) intermixing induced by ion implantation and thermal annealing. Different strain development in QWs (determined by STM topography of elastic relaxation in cross sectionally cleaved samples) is found to be dependent upon the range of the implanted ions relative to the QWs. It is found that the quantum wells remain latticed matched to the barrier layers after intermixing when ions are implanted through the multiple quantum well (MQW) stack. A shallow implantation in which ions are implanted into the cap layer above the MQW stack leads to tensilely strained wells and compressively strained interfaces between wells and barriers. The strain development in the latter case is attributed to different degrees of interdiffusion on the group III and group V sublattices. Finite element elastic computations are used to extract the group V and group III interdiffusion length ratio, and results using different diffusion models are compared. A preferred group V interdiffusion in the case of shallow implantation is explained in terms of faster diffusing P related defects compared to In related defects. Images of as-grown QWs provide useful information about the growth technique related compositional fluctuations at the interfaces.

Scanning tunneling microscopy is used to study low temperature grown (LTG) InGaAs with and without Be doping. The Be-doped material is observed to contain significantly fewer AsGa antisite defects than the undoped material, with no evidence found for Be–As complexes. Annealing of the LTG-InGaAs forms precipitates preferentially in the undoped material. The previously observed dependence of the optical response time on Be doping and annealing is attributed to changes in the As antisite concentration and the compensation effect of the Be.

InGaN alloys with indium compositions ranging from 0–40% have been grown by molecular beam epitaxy. The dependence of the indium incorporation on growth temperature and group III/group V ratio has been studied. Scanning tunneling microscopy images, interpreted using first-principles theoretical computations, show that there is strong indium surface segregation on InGaN. Based on this surface segregation, a qualitative model is proposed to explain the observed indium incorporation dependence on the growth parameters.

Strain-compensated InGaAsP/InGaP superlattices are studied in cross section by atomic force microscopy and scanning tunneling microscopy. Undulations in the morphology of the {110} cross-sectional faces are observed, and are attributed to elastic relaxation of this surface due to underlying strain arising from thickness and compositional variations of the superlattice layers. Finite element computations are used to extract a quantitative measure of the strain variation.

Using n-doped InGaAs/InP multi-quantum-well samples we compare measurements of ion-beam-induced quantum well broadening made by cross-sectional scanning tunneling microscopy and cross-sectional scanning transmission electron microscopy with the broadening calculated from the blueshift of the low temperature photoluminescence peak using different models of the intermixing process. Results are consistent with a simple square well model used to interpret photoluminescence shifts, but disagree with a model of separate Fick’s law diffusion on group III and V sublattices.