Role of Minority-Carrier Diffusion in Photoreflectance Measurements of Epitaxial GaAs Wafers

Publisher Website
Google Scholar
Abstract
Minority-carrier diffusion, instead of direct penetration of pump light, can be a dominant factor which determines the probed region in photoreflectance measurements of epitaxial GaAs wafers. Appearance of Franz-Keldysh oscillations (FKOs) originating from epitaxial layer/substrate interfaces is found to critically depend on the penetration depth of pump light relative to the surface depletion-layer width. This relationship indicates the importance of generation and diffusion of minority carriers within the neutral region, which can induce photoreflectance from unexpectedly deep locations. By inserting a potential barrier (a doped AlAs layer) into the path for minority-carrier diffusion, such a FKO component is shown to be eliminated. The experiment confirms that the sample under study is indeed in the diffusion-limited regime, and at the same time, provides a simple method which allows an accurate evaluation of the FKOs from the doped region (surface depletion layer), which usually is of interest from technological aspects.