A new in situ III-V surface characterization technique: chemical modulation spectroscopy

Abstract

A new in situ technique for the study of the molecular beam epitaxy (MBE) growth process of III–V compounds based on the chemical modulation of the surface has been developed. In this technique, the anisotropic optical reflectivity is modulated by a periodic variation of the surface stoichiometry induced by using group V pulsed molecular beams. Pulses are produced by valved pulsed cells for group V elements (As, P, Sb) that we use for atomic layer molecular beam epitaxy (ALMBE) growth. The substrate is maintained at sufficiently high temperature in order to obtain rapid desorption of group V molecules from surface during flux interruptions, and the process is monitorized by reflection high energy electron diffraction (RHEED). Linearly polarized light, reflected at near normal incidence by the sample, is collected independently along one of the two principal axes of the crystal, [1 1 0] and [1 Image 0]. This technique has been applied to the surfaces of epitaxial (1 0 0) layers of GaP, GaAs, GaSb, InP, InAs, and InSb grown by MBE. Spectra in the 1–3 eV range show well defined peaks for light polarized along [1 1 0] and [1 Image 0] directions, parallel to group III and group V dimers, at specific energies for each compound.