Electroreflectance in GaAs

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 a.c. 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 between parabolic edges of the M 0 type and saddle-point edges of the M 1 type.