Photovoltaic effects on Franz–Keldysh oscillations in photoreflectance spectra: Application to determination of surface Fermi level and surface recombination velocity in undoped GaAs∕n-type GaAs epitaxial layer structures

Abstract

We demonstrate that the surface Fermi level and surface recombination velocity in undoped GaAs∕n-type GaAs (i-GaAs∕n-GaAs) epitaxial layer structures can be simultaneously estimated from Franz–Keldysh oscillations (FKOs) in photoreflectance spectra, taking account of the photovoltaic effects. Initially, we performed computational studies on the surface electric fields in i-GaAs∕n-GaAs structures under the illumination of a probe beam. The surface electric-field strength is sensitive to the surface Fermi level and surface recombination velocity. We have found that these parameters can be evaluated from the dependence of the surface electric-field strength on the probe-beam power density. Next, we estimated experimentally the surface Fermi level and surface recombination velocity in an as-grown i-GaAs∕n-GaAs structure by analyzing the photovoltaic effect on the FKOs. The period of the FKOs increases with a decrease in the probe-beam power density. The surface Fermi level and surface recombination velocity are estimated from the probe-beam power dependence of the surface electric-field strength that is obtained from the analysis of the FKOs. We have also applied the analysis of the photovoltaic effect to the assessment of the GaAs surfaces exposed to the nitridation and the catalytic chemical vapor deposition of SiNx. In addition, we have derived a line-shape function of the FKOs from i-GaAs∕n-GaAs structures, which is applicable even to the FKOs influenced by a probe-beam interference phenomenon in a layered structure.