Photoluminescence studies of heteroepitaxial GaAs on Si

The authors present a systematic study of the photoluminescence of undoped GaAs layers deposited by MOCVD on Si substrates. The study includes an examination of substrate and layer thickness effects in thin GaAs layers, and a detailed investigation of the stress effects on the intrinsic band-edge transitions in thicker samples. For sample thickness, t less than or equal to 0.5 mu m, they observe strong midgap emission bands associated with defects close to the interface. These bands depend strongly on the nature of the Si substrate. The crystal quality improves with sample thickness, and for t greater than or equal to 0.5 mu m the emission is dominated by lines in the band edge region which are relatively independent of substrate preparation. Photoluminescence excitation spectra reveal that the highest energy line is due to an intrinsic exciton transition, and that a splitting of this line observed for t greater than or equal to 2 mu m reflects the presence of two different regions of strain in the material.