DEEP-LEVEL OPTICAL SPECTROSCOPY OF ZNTE

The variation of the deep-level spectrum of stoichiometric ZnTe in the various stages of its purification and annealing in saturated Zn vapo r has been studied by low-temperature photoluminescence and IR Fourier spectroscopy. The relation between the concentration of the main resi dual impurities with complex formation probability is analyzed. We hav e succeeded in observing for the first time Z center emission in ZnTe, as previously in CdTe and ZnSe. This center is shown to be a multicha rged impurity in ZnTe. The activation energies of these levels have be en determined. A comparison of the data obtained by chemical analysis with optical spectra has led to a conclusion that this center is assoc iated with isolated oxygen present on the metalloid sublattice. While this emission exhibits the same specific features in a number of II-VI compounds (a high recombination rate, narrow emission lines, extremel y weak electron-phonon coupling), the positions of the levels in the b and gap and the characteristic charge state distinguish ZnTe from CdTe and ZnSe. As a rule, the Z center forms in a material in decompositio n of various complexes (for instance, of the complex responsible for t he 1.65-eV emission in ZnTe) and disappears when the material is doped leading to formation of the same complexes. An assumption is put forw ard that this center creates the main compensating deep levels and is an essential component of easily forming complexes with impurities. It s position in the lower half of the ZnTe band gap (in contrast to ZnSe and CdTe) makes preparation of the n material difficult. (C) 1988 Ame rican Institute of Physics.