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 don or-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 u ndoped material after annealing using diamond-like C (DLC) caps, while the A2 level is observed in nominally Na-doped material. The ionizati on energies of these levels are accurately determined from the tempera ture dependence of the band-to-acceptor (e-A0) peak positions, account ing 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 f it well to effective mass theory, while those for P do not. A model fo r the strain splitting of shallow acceptor-bound excitons has been dev eloped and confirmed using measurements on samples whose substrates ha ve 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.