Donor levels and the microscopic structure of theDXcenter inn-type Si-dopedAlxGa0.51−xIn0.49P grown by molecular-beam epitaxy

Abstract

We have investigated donor levels and the local structure of DX centers in Si-doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{0.51\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{In}}_{0.49}$P grown by gas-source molecular-beam epitaxy. In a ternary alloy ${\mathrm{Ga}}_{0.51}$${\mathrm{In}}_{0.49}$P, Si donors form only shallow donor states. In contrast, in quaternary alloys with x\ensuremath{\ge}0.25 a deep electron trapping center is observed. Hall measurements reveal an activated behavior of the mobile electron concentration, and the thermal binding energy of the dominant donor state is \ensuremath{\sim}0.1 eV when the Al fraction is x=0.25. Illumination with infrared or red light results in persistent photoconductivity at T\ensuremath{\le}120 K. The appearance of the DX level in the band gap around x\ensuremath{\approxeq}0.1 gives a consistent picture of the experimental findings. Positron annihilation spectroscopy shows that the Si DX center is a vacancylike defect with a local structure equivalent to that found earlier in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As. The very different core shell structures of the group-III (Ga, In) and group-V (P) atoms give direct evidence that the vacancy has P atoms as its nearest neighbors and we identify it as a vacancy in the group-III sublattice. The structural data give support to the vacancy-interstitial model, which predicts that the donor impurities can take two different configurations in sp-bonded semiconductors. \textcopyright{} 1996 The American Physical Society.