SYSTEMATIC INVESTIGATION OF SHALLOW ACCEPTOR LEVELS IN ZNSE

A systematic investigation of shallow acceptor levels in ZnSe grown by molecular beam epitaxy (MBE) has been performed using low temperature photoluminescence (PL) measurements as a function of excitation level, temperature, strain, and laser energy (i.e., selectively excited donor-acceptor pair luminescence or SPL). Five of the levels are due to N, Li, As, P, and O, while the chemical origins of two levels, denoted A1 and A2, have not yet been determined. The A1 level is observed in undoped material after annealing using diamond-like C (DLC) caps, while the A2 level is observed in nominally Na-doped material. The ionization energies of these levels are accurately determined from the temperature dependence of the band-to-acceptor (e-A0) peak positions, accounting for strain. Those energies are 114.3 +/- 0.5, 114.2 +/- 0.3, 111.3 +/- 0.5, 106.1 +/-0.6, 95.0 +/- 0.4, 88.4 +/- 0.5, and 83 +/- 3 meV, respectively, for As, Li, N, Al, A2, P, and O in unstrained material. Several excited states have been observed in SPL measurements for As, A2, O, and P for the first time. The excited states of As, O, and A2 fit well to effective mass theory, while those for P do not. A model for the strain splitting of shallow acceptor-bound excitons has been developed and confirmed using measurements on samples whose substrates have been removed. Haynes's Rule is shown to be inapplicable to shallow acceptors in ZnSe. A strain splitting of the (e-A0) peak for As or Li acceptors in annealed material is clearly resolved and modeled.