We examine the morphological evolution of growing surfaces using Monte Carlo simulations of a solid-on-solid model. We use direct comparisons with experiment both to identify the kinetic processes that must be included in a model for GaAs(001) homoepitaxy and to parametrize the rates of these processes. We first examine the evolution of a vicinal surface during the first few monolayers of growth and compare the density of surface steps of the simulated surfaces with reflection high-energy electron-diffraction measurements. By including both a non-thermal incorporation step of freshly deposited atoms and a barrier to interlayer atomic transport, excellent quantitative agreement is obtained for an entire range of growth conditions, including the relaxation of the surface toward equilibrium upon the termination of the beam. We then examine the morphology as successively more layers are grown and find that the surface evolves into a self-organized state wherein the local slope of the growing features remains approximately constant with time.
The solid-on-solid model, with nearest- and next-nearest neighbour interactions, of two-dimensional nucleation on the surface of a crystal in unstable equilibrium with its supersaturated vapour allows from the local mean direction of curved step to derive closed formulae for the shape, the area, and the activation energy for growth of the crystal nucleus. The formulae facilitate to estimate from the observed shape patterns the parameters of nucleation, to follow the evolution of the crystal nucleus with temperature and the dependence of activation energy on distance between screw dislocations which provide steps on the crystal surface.
Gallium nitride bulk crystals grown at about 15 kbar and 1500 K have been examined by using the high resolution X-ray diffractometry. An analysis of a set of the rocking curves of various Bragg reflections enabled us to estimate a dislocation density. For the crystals of dimensions lower than about 1 mm it is lower than 10^{-5} cm^{-2}. For bigger samples the crystallographic quality worsens. With an application of the reciprocal lattice mapping we could distinguish between internal strains and mosaicity which are both present in these crystals The results for the bulk crystals are compared with those for epitaxial layers.
This paper discusses molecular beam epitaxy with particular emphasis on the production of state of the art electronic and optoelectronic low dimensional structures and devices. The molecular beam epitaxy process is outlined briefly and the practical problems associated with producing "state of the art" (Al,Ga)As/GaAs structures are considered. Examples include high mobility electron and hole gases, low threshold current lasers and the multi-quantum well solar cells.
The first results obtained with the use of Ga_{2}S_{3} and Ga_{2}Se_{3} compounds as sources of donor elements for molecular beam epitaxy of Al_{x}Ga_{1-x}Sb (0 ≤ x ≤ 1) and Al_{x}Ga_{1-x}As (0 ≤ x ≤ 0.4) are reported. In GaAs free electron concentrations obtained when incorporating the donors from these sources can be easily controlled in the range of three orders of magnitude. For Al_{x}Ga_{1-x}Sb it was possible to compensate the high concentration of native acceptors and to obtain n-type of conductivity.
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