InP and GaAs characterization with variable stoichiometry obtained by molecular spray

Both InP and GaAs surfaces were studied in parallel. A molecular spray technique was used to obtain two semiconductor surfaces with different superficial compositions. The structures of these surfaces were examined by electron diffraction. Electron energy loss was measured spectroscopically in order to determine surface electrical characteristics. The results are used to support conclusions relative to the role of surface composition in establishing a Schottky barrier effect in semiconductor devices

Scaling of Heteroepitaxial Island Sizes

Monte Carlo simulations of an atomistic solid-on-solid model are used to study the effect of lattice misfit on the distribution of two-dimensional islands sizes as a function of coverage $\Theta$ in the submonolayer aggregation regime of epitaxial growth. Misfit promotes the detachment of atoms from the perimeter of large pseudomorphic islands and thus favors their dissolution into smaller islands that relieve strain more efficiently. The number density of islands composed of $s$ atoms exhibits scaling in the form \mbox{$N_s(\Theta) \sim \Theta / \langle s \rangle^2 \, g(s/\langle s \rangle$)} where $\langle s \rangle$ is the average island size. Unlike the case of homoepitaxy, a rate equation theory based on this observation leads to qualitatively different behavior than observed in the simulations.Comment: 10 pages, LaTeX 2.09, IC-DDV-94-00

Crystal growth and elasticity

The purpose of this paper is to review some elasticity effects in epitaxial growth. We start by a description of the main ingredients needed to describe elasticity effects (elastic interactions, surface stress, bulk and surface elasticity, thermodynamics of stressed solids). Then we describe how bulk and surface elasticity affect growth mode and surface morphology by means of stress-driven instability. At last stress-strain evolution during crystal growth is reported.Comment: 12 page

Influence of the mirrors on the strong coupling regime in planar GaN microcavities

The optical properties of bulk $\lambda/2$ GaN microcavities working in the strong light-matter coupling regime are investigated using angle-dependent reflectivity and photoluminescence at 5 K and 300 K. The structures have an Al$_{0.2}$Ga$_{0.8}$N/AlN distributed Bragg reflector as the bottom mirror and either an aluminium mirror or a dielectric Bragg mirror as the top one. First, the influence of the number of pairs of the bottom mirror on the Rabi splitting is studied. The increase of the mirror penetration depth is correlated with a reduction of the Rabi splitting. Second, the emission of the lower polariton branch is observed at low temperature in a microcavity containing two Bragg mirrors and exibiting a quality factor of 190. Our simulations using the transfer-matrix formalism, taking into account the real structure of the samples investigated are in good agreement with experimental results.Comment: published versio

Electronic structure of wurtzite and zinc-blende AlN

The electronic structure of AlN in wurtzite and zinc-blende phases is studied experimentally and theoretically. By using x-ray emission spectroscopy, the Al 3p, Al 3s and N 2p spectral densities are obtained. The corresponding local and partial theoretical densities of states (DOS), as well as the total DOS and the band structure, are calculated by using the full potential linearized augmented plane wave method, within the framework of the density functional theory. There is a relatively good agreement between the experimental spectra and the theoretical DOS, showing a large hybridization of the valence states all along the valence band. The discrepancies between the experimental and theoretical DOS, appearing towards the high binding energies, are ascribed to an underestimation of the valence band width in the calculations. Differences between the wurtzite and zinc-blende phases are small and reflect the slight variations between the atomic arrangements of both phases

Wetting layer thickness and early evolution of epitaxially strained thin films

We propose a physical model which explains the existence of finite thickness wetting layers in epitaxially strained films. The finite wetting layer is shown to be stable due to the variation of the non-linear elastic free energy with film thickness. We show that anisotropic surface tension gives rise to a metastable enlarged wetting layer. The perturbation amplitude needed to destabilize this wetting layer decreases with increasing lattice mismatch. We observe the development of faceted islands in unstable films.Comment: 4 pages, 3 eps figure

Analysis of the characteristic temperatures of (Ga,In)(N,As)/GaAs laser diodes

The characteristic temperatures of the threshold current density, T0, and external differential quantum efficiency, T1, of a series of (Ga,In)(N,As)/GaAs quantum well (QW) laser diodes are measured in the wavelength range from 1 to 1.5μm. It is found that both T0 and T1 strongly decrease with increasing lasing wavelength. The origin of this degradation is shown to be, in the case of T0, mostly dominated by a decrease in the transparency current density characteristic temperature, an increase in the optical losses and a decrease in the modal gain. The degradation of T1 is mainly due to the increase in the optical losses. The effective carrier recombination lifetime in the QW is shown to decrease from 1.2 to 0.2 ns with N content up to 2%, in good agreement with previous reports that link this low lifetime to non-radiative monomolecular recombination through defects in the QW. Carrier leakage is ruled out as the dominant process degrading T0 and T1 on the basis of the temperature dependence of the effective carrier recombination lifetime

Elastic relaxation during 2D epitaxial growth: a study of in-plane lattice spacing oscillations

The purpose of this paper is to report some new experimental and theoretical results about the analysis of in-plane lattice spacing oscillations during two-dimensional (2D) homo and hetero epitaxial growth. The physical origin of these oscillations comes from the finite size of the strained islands. The 2D islands may thus relax by their edges, leading to in-plane lattice spacing oscillations during the birth and spread of these islands. On the one hand, we formulate the problem of elastic relaxation of a coherent 2D epitaxial deposits by using the concept of point forces and demonstrate that the mean deformation in the islands exhibits an oscillatory behaviour. On the other hand, we calculate the intensity diffracted by such coherently deposited 2D islands by using a mean model of a pile-up of weakly deformed layers. The amplitude of in-plane lattice spacing oscillations is found to depend linearly on the misfit and roughly linearly on the nucleation density. We show that the nucleation density may be approximated from the full-width at half maximum of the diffracted rods at half coverages. The predicted dependence of the in-plane lattice spacing oscillations amplitude with the nucleation density is thus experimentally verified on V/Fe(001), Mn/Fe(001), Ni/Fe(001), Co/Cu(001) and V/V(001).Comment: 39 pages, 10 figure

Quantum modeling of semiconductor gain materials and vertical-external-cavity surface-emitting laser systems

This article gives an,overview of the microscopic theory,theory used to quantitatively model a wide range of semiconductor laser gain materials. As a snapshot of the current state of research, applications to a variety of actual quantum-well systems are presented. Detailed theory experiment comparisons are shown and it is analyze how the theory can be used to extract poorly known material parameters. The intrinsic laser loss processes due to radiative and nonradiative Auger recombination are evaluated microscopically. The results are used for realistic simulations of vertical-external-cavity surface-emitting laser systems. To account for nonequilibrium effects, a simplified model is presented using pre-computed microscopic scattering and dephasing rates. Prominent deviations from quasi-equilibrium carrier distributions are obtained under strong in-well pumping conditions