Conduction-band-to-acceptor magnetoluminescence in zinc telluride

Abstract

We report on the magnetic field behavior of free-to-bound (FB) acceptor luminescence and donor absorption in high-purity $p$-type ZnTe. Conduction-band Landau level states are readily seen in the acceptor FB luminescence, and yield the best current estimate of the electron effective mass in ZnTe, $\frac{{m}_{e}^{*}}{{m}_{0}}=0.116\ifmmode\pm\else\textpm\fi{}0.005$, significantly different from most previous values. Spin splitting is also seen, and yields approximate hole and electron $g$ values in agreement with recent estimates from acceptor bound-exciton (BE) luminescence, as near as can be determined. These results confirm a small negative electron $g$ value, far from that predicted by first-order $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}$ theory. This discrepancy shows that interactions with higher bands are important in ZnTe. We use a five-band model together with our experimental values of ${m}_{e}^{*}$ and ${g}_{e}$ to determine the matrix elements ${P}^{2}$ and ${{P}^{\ensuremath{'}}}^{2}$ of the interaction between the conduction band and, respectively, the valence and next-higher conduction bands. We find ${P}^{2}=32.3$ eV and ${{P}^{\ensuremath{'}}}^{2}=7$ eV, close to values in GaAs. The polaron mass enhancement is about 5% for the electron in ZnTe. The electrons recombine with an effective temperature of \ensuremath{\sim} 14 K at a lattice temperature of \ensuremath{\sim} 5 K under typical experimental conditions. The magnetic field causes strong enhancement of "two-hole" BE luminescence satellites involving $p$-like acceptor excited states caused by mixing with $s$ states for an acceptor with large central-cell contribution to its binding energy, possibly an effect of relatively long-range terms due to misfit strain. The zero-field positions of the acceptor FB band suggest that ${E}_{g}$ is close to 2.394 eV in ZnTe at 4.2 K according to recent independent estimates of the acceptor ionization energies from these BE satellites. This, in turn, implies an internal binding energy of the free exciton close to 13 meV, significantly larger than previous values, \ensuremath{\sim}10 meV. Large magnetic effects occurring within an absorption edge located just below the main acceptor BE line are tentatively attributed to the onset of a BE state at ionized donors, stabilized in the magnetic field.