CHARGE-DENSITY PROFILES OF CLOSE SPACED VAPOR TRANSPORT GAAS EPITAXIAL LAYERS

GaAs epitaxial films have been deposited on heavily Si-doped (100) GaAs substrates by closely spaced vapor transport from a semi-insulating (undoped) GaAs source. Charge density (N) profiles of the epitaxies have been determined electrochemically by a succession of photocorosion steps and capacitance measurements. When the films are thick enough, typical N profiles show four regions. Starting from the surface of the film and going toward the GaAs substrate, there is a first region (I) of constant N, extending over a length varying with the deposition time. It is followed by a second region (II) extending over 12±2μm, where N slowly rises. In region III, there is an abrupt increase of N followed by region IV which is the substrate region.