Photocurrent anisotropy in compositional modulated superlattice of long-range ordered Ga_0.5In_0.5P

Abstract

Photocurrent anisotropy of long-range ordered Ga_0.5In_0.5P alloys has been sys-tematically investigated. The ordered Ga_0.5In_0.5P is a compositional modulated superlattice of Ga_0.5+η/2In_0.5-η/2P and Ga_0.5-η/2In_0.5+η/2P monolayer planes, where η is a long-range order parameter. The photocurrent edge of the [110] polarization is lower than that of the$[1{\text{ }}\overline {\text{1}} 0]$. The observed anisotropy in the photocurrent spectra is due to a crystal-field splitting at the valence-band maximum in ordered Ga_0.5In_0.5P. The anisotropy shows a continous variation as a function of η. In order to make clear the effects of the valence-band splitting on the polarized photocurrent spectra, we performed theoretical calculations in which a distribu-tion of η in the epitaxial film and an order-parameter dependence of oscillator strength were considered. From these calculations, it is found that oscillator strength is a key parameter in the anisotropic character. The calculated results moderately agree with the measured data. Furthermore, the epitaxial thickness dependence of the anisotropic character in photocurrent was investigated.