AS CAPTURE AND THE GROWTH OF ULTRATHIN INAS LAYERS ON INP

Modification of (001) InP surfaces in the absence of P and by As capture in the absence and presence of In is investigated under chemical beam epitaxy conditions by virtual-interface analysis of real-time kinetic ellipsometric (KE) data. In the absence of anion flux, from 490 to 520-degrees-C the surface roughens microscopically at a rate of 0.06 angstrom/s at 518-degrees-C, with the rate described by an activation energy of 5.3 eV. Consistent with this stability, As that accumulates on the surface under As exposure in the absence of growth can be completely removed by subsequent exposure to P, showing that As exchange is limited to the outer layer. However, As can be captured permanently by resuming InP growth before the surface has been completely purged of As or by codepositing In, thus producing ultrathin regions of InAs. Using the virtual-substrate approximation, we determine the amounts of captured As to submonolayer precision from the associated displacements of the trajectories of the ellipsometrically measured pseudodielectric function [epsilon] without any knowledge. about the underlying layers. Photoluminescence data show that these layers are not entirely uniform but exhibit lateral thickness variations. Independent assessments of monolayer amounts of captured As by secondary-ion-mass spectrometry (SIMS) differ by a factor of two from the KE results, which may be due to layer inhomogeneity or a modified SIMS ionization sensitivity for very thin layers.