CONDUCTION-BAND INTERVALLEY SPACING IN ZINC SELENIDE OBTAINED FROM THE PHOTOIONIZATION SPECTRUM OF A DEEP-LEVEL

The photoionization spectrum of a level in the upper half of the band gap of zinc selenide has been measured. There are two thresholds, at 0 .46 and 1.72 eV. These are assigned to transitions from the level to t he GAMMA valley and to a set of higher valleys, giving an intervalley spacing of 1.26 eV in agreement with the pseudopotential calculations of J. R. Chelikowsky and M. L. Cohen [Phys. Rev. B 14, 556 (1976)]. Th e level concentration is 3 X 10(14) cm-3. Thermal-emission experiments give an apparent activation energy 0.33 eV and an apparent capture cr oss section 1.4 X 10(-14) cm2, values similar to those obtained by oth er authors for a level in ZnSe by deep-level trap spectroscopy. In the zinc selenide sample used here, there are no other levels with simila r concentration in the upper half of the band gap.