Systematic investigation of shallow acceptor levels in ZnSe

Abstract 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 A 1 and A 2 , have not yet been determined. The A 1 level is observed in undoped material after annealing using diamond-like C (DLC) caps, while the A 2 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-A 0 ) 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, A 1 , A 2 , P, and O in unstrained material. Several excited states have been observed in SPL measurements for As, A 2 , O, and P for the first time. The excited states of As, O, and A 2 fit well to effective mass theory, while those for P do not. A model for the strain splitting of shallow acceptor-bound excitions has been developed and confirmed using measurements on samples whose substrates have been removed. Hayne's Rule is shown to be inapplicable to shallow acceptors in ZnSe. A strain splitting of the (e-A 0 ) peak fo As or Li acceptors in annealed material is clearly resolved and modeled.