NATURE OF PREDOMINANT ACCEPTORS IN HIGH-QUALITY ZINC TELLURIDE

We report very sharp bound exciton luminescence spectra in high quality melt-grown very lightly compensated ZnTe, p-type with NA-ND in the low 10+15 cm-3. Bound exciton localisation energies at seven shallow neutral acceptors with EA between ~55 and ~150 meV are very insensitive to EA. Optical absorption and dye laser luminescence excitation spectroscopy were necessary to obtain a full separation of the transitions due to different acceptors, together with a study of certain 'two-hole' luminescence satellites in which the acceptor is left in a series of orbital states after bound exciton decay. Two shallow acceptors are PTe and AsTe, a third possibly LiZn while a fourth, relatively prominent in our best undoped crystals, may be a complex. A deeper, 150 meV acceptor, frequently reported in the ZnTe literature and electrically dominant in most of our undoped crystals has the Zeeman character of a point defect. We present clear evidence from our spectra that this energy does not represent the binding of a single hole at a doubly ionized cation vacancy, a popular attribution since 1963. This acceptor may be covered by another impurity, possibly CuZn. We also report bound phonon effects, lifetime broadening of excited bound exciton states and observe a single unidentified donor with ED ~18.5 meV. This energy is determined using selective dye laser excitation at the weak neutral donor bound exciton line and from the onset of valence band to ionized donor photo-absorption. © 1978.