An investigation was made of the donor levels and local structure of DX centers in Si-doped AlxGa0.51-xIn0.49P that had been prepared by means of gas-source molecular beam epitaxy. In the ternary alloy, Ga0.51In0.49P, the Si donors formed only shallow donor states. In quaternary alloys, when x was greater than 0.25, a deep electron-trapping center was observed. Hall measurements revealed an activated behavior of the mobile electron concentration, and the thermal binding energy of the dominant donor state was about 0.1eV when the x-value was 0.25. Illumination with infra-red or red light resulted in persistent photoconductivity at temperatures of up to 120K. Positron annihilation spectroscopy showed that the Si DX center was a vacancy-like defect with a local structure which was equivalent to that found previously in AlGaAs. The very different core shell structures of the group-III (Ga, In) and group-V (P) atoms provided direct evidence that the vacancy had P atoms as its nearest neighbors, and it was identified as being a vacancy in the group-III sub-lattice. The structural data supported the vacancy-interstitial model, which predicted that donor impurities could take on 2 different configurations in sp-bonded semiconductors.

J.Mäkinen, T.Laine, J.Partanen, K.Saarinen, P.Hautojärvi, K.Tappura, T.Hakkarainen, H.Asonen, M.Pessa, J.P.Kauppinen, K.Vänttinen, M.A.Paalanen, J.Likonen: Physical Review B, 1996, 53[12], 7851-62