Ionization energy of the shallow nitrogen acceptor in zinc selenide

Evidence on the presence and binding energy of the shallow N acceptor is obtained for growth-doped liquid-phase-epitaxial (LPE) and organometallic chemical-vapor-deposited (OMCVD) ZnSe thin single-crystal layers. The small increase in N-acceptor bound-exciton (BE) binding energy $E_{\mathrm{BX}}$ relative to the Li acceptor, 0.3 meV, is clearly established from intercomparison of spectral features and use of tunable dye-laser spectroscopy. The LPE crystals contain a new unidentified donor $E_D=26.8\mathrm{}$ meV, as well as In and Al minor donors, while the dominant donor in these OMCVD crystals is Ga. Selectively excited donor-acceptor-pair (DAP) luminescence spectra contain a satellite structure which provides an estimate of ${\left(E_A\right)}_{\mathrm{N}}=111\mathrm{}\pm 1$ meV, distinctly 2.2±0.5 meV shallower than the Li acceptor but ∼21 meV deeper than some previous estimates from LPE ZnSe:N. This estimate is confirmed by $A^0$,$X$ BE "two-hole" satellites observed under strong optical pumping. The effective-mass value of $E_A$ is placed close to 110 meV. The dependence of displacement energy of this structure on DAP separation is very significant in the comparison of Li and N acceptors. The relationship of $E_{\mathrm{BX}}$ and $E_A$ is retrograde for the shallowest acceptors N, Li, and Na so far identified in ZnSe. Sharp differences between the excitation spectra of BE photoluminescence between $n$-type ZnSe and $p$-type ZnTe doped to comparable concentrations are discussed. It is concluded that the best N-doped OMCVD ZnSe yet available is still $n$ type due to residual donors.