EDGE EMISSION AND PHONON EFFECTS IN PHOTOLUMINESCENCE OF CDTE

In the photoluminescence spectra of CdTe four series of lines can be resolved in the temperature range 4.2 to 78 °K; each of them is due to the electron transitions involving LO phonons (I. II. III, IV). The relative intensities of these series (the zero‐phonon lines at 1.528; 1.539; 1.548; and 1.556 eV at 20°K) depend on the sample temperature and the present impurities. The series I and II are similar in their intensity dependence on temperature to the so‐called LT (low temperature, long wavelength) and HT (high temperature, short wavelength) series of the green edge emission of CdS. Series I is dominant in crystals doped with shallow donors; this fact in connection with the temperature dependence and the dependence of the line shape on the excitation intensity leads to the conclusion that it is due to radiative transitions between shallow donors (ED = 0.015eV) and acceptors (EA = 0.0067 eV). The temperature dependence of the intensity of series II and the lines' shape suggest that this series is due to radiative transitions of electrons from the conductivity band to acceptor levels (EA = 0.0067 eV). The variation of the relative intensities of series I and II with the type and content of impurities in the samples correlates with the variation of the relative intensities of the lines in the 1.59 eV region ascribed to the exciton annihilation at donors and acceptors. The distribution of phonon replica intensities in series I and II corresponds to the expression In = I0Nn/n!(n = 0,1,2,…). The changes of the parameter N observed in some cases are due to the overlapping of series I and II with the series III or IV. the nature of which is not quite clear. The variation of the parameter N (which depends on the intensity of the electron‐phonon interaction) with the level depth is found to agree qualitatively with the theory of Hopfield. The band at 0.50 eV corresponding to the transitions involving deeper levels shows a structure which may be due to the interaction of electron transitions with local phonons having an energy of 0.045 eV. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim