AS CAPTURE AND THE GROWTH OF ULTRATHIN INAS LAYERS ON INP

Modification of (001) InP surfaces in the absence of P and by As captu re in the absence and presence of In is investigated under chemical be am epitaxy conditions by virtual-interface analysis of real-time kinet ic 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 a ngstrom/s at 518-degrees-C, with the rate described by an activation e nergy of 5.3 eV. Consistent with this stability, As that accumulates o n the surface under As exposure in the absence of growth can be comple tely 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. Us ing the virtual-substrate approximation, we determine the amounts of c aptured As to submonolayer precision from the associated displacements of the trajectories of the ellipsometrically measured pseudodielectri c function [epsilon] without any knowledge. about the underlying layer s. Photoluminescence data show that these layers are not entirely unif orm 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 du e to layer inhomogeneity or a modified SIMS ionization sensitivity for very thin layers.