Selective pair luminescence was used to identify shallow acceptor levels in undoped epilayers which had been grown, by means of molecular beam epitaxy, under ultra-high vacuum. The low-temperature photoluminescence spectra were typical of high-purity material. Unlike conventional molecular beam epitaxially grown undoped material, where the near-bandedge excitonic luminescence was dominated by acceptor-bound excitons, the near-band-edge luminescence of the present samples was dominated by donor-bound excitons. The ground and excited acceptor states indicated that CAs was the main residual acceptor impurity in the layer. The existence of a donor-acceptor pair emission band demonstrated that a second acceptor was electronically active. Excited-state spectroscopy identified the second residual acceptor as being ZnGa. This was hardly ever observed under the usual conditions.

Donor-Acceptor Pair Spectroscopy of GaAs Grown in Space Ultra-Vacuum G.Neu, M.Teisseire, A.Freundlich, C.Horton, A.Ignatiev: Applied Physics Letters, 1999, 74[22], 3341-3