IMPROVEMENT OF LIFE TIME OF MINORITY-CARRIERS IN GAAS EPI-LAYER GROWNON GE SUBSTRATE

A buffer layer structure on Ge substrate was studied for MOCVD growth of a high-quality GaAs layer. The buffer layer structure was designed taking into consideration both lattice constants and thermal expansion coefficients of GaAs and Ge. It consisted of a preliminarily grown th in layer of AlxGa1-xAs and a GaAs layer. Photoluminescence (PL) decay of a GaAs layer in an Al0.2Ga0.8As-GaAs-Al0.2Ga0.8As double-hetero (DH ) structure, which was grown on the buffer layer structure, was observ ed by time-resolved PL method to estimate the quality of epilayers in the DH structure. The PL decay time strongly depended on Al content (x ) of the AlxGa1-xAs preliminary layer, and the highest value was obtai ned when the x was 0.25. A PL decay time above 20 ns was successfully obtained for the DH structure grown on the buffer layer structure, whi ch consisted of a 0.05 mu m thick Al0.25Ga0.75As layer and a 1 mu m th ick GaAs layer. Although this value was half of that for the DH struct ure grown on GaAs substrate, it was much longer than the value of 3 ns for the DH structure grown on Ge substrate with a conventional GaAs b uffer layer 1 mu m thick.