Electroreflectance Studies in GaAs

Abstract

Measurements of the electroreflectance effect on GaAs surfaces in the range of photon energies from 1.3 to 4.5 eV are reported. If an ac electric field modulates the surface potential in the reflecting surface, the reflectance responds in a sequence of pronounced peaks at the photon energies of interband transitions, as they are known from previous analysis of the band structure. However, the high resolution and sensitivity of this derivative technique adds a new kind of information. The shift of the observed groups of peaks with electric field establishes an experimental criterion which discriminates among parabolic edges of the M0 type and saddle-point edges of the M1 type. This provides, for the first time, an unambiguous guideline for the phase of band structure analysis which deals with the assignment of structure in the optical properties to interband transitions. Strong structure in the reflectance response below the fundamental absorption edge is tentatively assigned to an absorption for which the initial state is an impurity level. Information gained from such structure below the fundamental edge, approximately coinciding with the photon energy of radiative transitions in GaAs, complements the large amount of work, experimental and theoretical, aimed at this spectral region, particularly in GaAs.