Vapour growth, EPR and optical study of Znse:Ti single crystals



Znse:Ti crystals were grown by seeded chemical vapour transport (SCVT) in a hydrogen atmosphere. In situ doping with titanium was carried out from an additional TiSe source in the quartz ampoule at 1460 K. The Good homogeneity of the Ti distribution and the presence of only a few defects have been demonstrated by etch pit and X-ray topography studies. For the frist time, Ti3+ (3d1) centres in a II–VI semiconductor compund are detected. The concentration of localized centres of Ti2+ and Ti3+ in high-resistivity material determined by EPR is about 5 × 1016 cm−3. Fe3+, Ni2+ and traces of Mn2+ are additionally observed. Below 77K an anisotropic EPR spectrum of Ti3+ (d1) is recorded, indicating both a dynamic and a static Jahn–Teller effect of the 2E(D) ground state. At lower temperatures clear evidence of the static Jahn–Teller effect is observed. The frist emission and excitation spectra of Ti impurities in II–VI compounds are presented. An emission near 3400 cm−1 is assigned to the 3T2(F) → 3A2(F) transition of Ti2+ (d2). Its excitation structures coincide with the known absorption bands to 3T1(P) and 3T1(F). A further structured luminescence band at 4700 cm−1 is related to 2T22E(D) transition of Ti3+ (d1). Ti ions form a deep donor level Ti2+/Ti3+ situated approximately 14,100 cm−1 above the valence band. This photo-ionization threshold is derived from the excitation measurements in accordance with previous photoconductivity experiments.