A NEW IN-SITU III-V SURFACE CHARACTERIZATION TECHNIQUE - CHEMICAL MODULATION SPECTROSCOPY

A new in situ technique for the study of the molecular beam epitaxy (M BE) 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 surf ace stoichiometry induced by using group V pulsed molecular beams. Pul ses are produced by valved pulsed cells for group V elements (As, P, S b) 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 f lux interruptions, and the process is monitorized by reflection high e nergy electron diffraction (RHEED). Linearly polarized light, reflecte d at near normal incidence by the sample, is collected independently a long one of the two principal axis of the crystal, [1 1 0] and [1 (1) over bar 0]. This technique has been applied to the surfaces of epitax ial (1 0 0) layers of GaP, GaAs, GaSb, InP, InAs, and InSb grown by MB E. Spectra in the 1-3 eV range show well defined peaks for light polar ized along [1 1 0] and [1 (1) over bar 0] directions, parallel to grou p III and group V dimers, at specific energies for each compound.