Donor discrimination and bound exciton spectra in InP

Abstract

We report detailed studies of the near-gap photoluminescence (NGPL) of refined vapor phase epitaxial (VPE) InP layers, selected to afford the best chance of resolving structure arising from the small chemical shifts between different donor species. Good general correlation was found between electrical data and the quality of the NGPL spectra in a survey of 50 crystals. In particular, the quality of the D+,X bound exciton (BE) and the ‘‘two-electron’’ donor satellites (TEDS) of the D0,Xn BE luminescence components correlated with the 77 °K mobility, known to be dominated by ionized impurity scattering. Use of selective excitation with a narrowed line from a dye laser and magnetic fields to obtain spectral components less subject to inhomogeneous broadening is discussed. The magnetic field is most effective in narrowing the TEDS components. The crystal quality, expressed mainly through the total concentration of shallow donors and acceptors, is apparently just inadequate to obtain line narrowing by selective excitation even in the best available crystals of VPE InP. However, selective excitation is still helpful in removing background luminescence and in enhancing luminescence satellites of particular D0, Xn BE components. Inhomogeneous broadenings of the various electronic states are contrasted. Measurements on both the D0, Xn′ TEDS and D+, X show evidence of only a single donor in the few samples with optimum linewidths. The general difference between these NGPL findings and far infra-red photoconductivity (FIRPC) measurements results from differential incorporation rates for the two most likely inadvertent shallow donor species, Si and S, during the growth of the VPE layers. The energy of the single NGPL donor suggests that it may be Si according to available FIRPC data. Resonantly enhanced Raman scattering (RERS) is observed both amongst the TEDS and through pure electron spin flip transitions. The D+, X and D0,h spectral features are well resolved, and Zeeman spectroscopy is consistent with the D+, X attribution. Approximate electron and hole g values are derived, together with more accurate values of ge from the RERS and of m*e from the TEDS magnetic splittings.