Radiative Recombination in Melt-Grown n -Type, Ge-Doped GaAs

Photoluminescence measurements were made of closely compensated, n-type GaAs grown by the horizontal Bridgman method. The ratio of Ge donors to Ge acceptors is estimated to be ∼1.25. At 77°K (n≅3× 1017 cm−3) emission bands are observed at 1.51, 1.49, and 1.22 eV. The second band is nearly comparable in intensity to the first in these materials and is ascribed to a recombination process involving a shallow Ge acceptor level. These data suggest that this level is located 0.02–0.03 eV above the valence band. The band at 1.22 eV is considerably more intense than the other bands. Evidence is presented suggesting that this band is due to a shallow donor to deep acceptor radiative transition. The shallow donor is probably Ge. The deep acceptor level is approximately 0.2 eV above the valence band and may involve a lattice defect particularly prominent in melt-grown GaAs. The low-energy emission band has been correlated with an absorption peak. On the basis of the absorption data, the deep acceptor concentration is roughly estimated to be of the order of 1016 cm−3.