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Zusammenfassung:
Bridgman-grown CdTe and (Cd, Zn)Te crystals doped with Ti are investigated by means of near-infrared optical spectroscopy and electron paramagnetic resonance (EPR). In high-resistivity CdTe material, Ti centres are detected by EPR with a concentration of abou 1016 cm-3. Below 60 K, the isotropic spectrum of the Ti2+(3d2) ground state 3A2(F) is recorded, showing strong saturation at lower temperatures. Below 8 K, a second spectrum appears due to transitions within the vibronic 2E ground state of Ti3+(3d1 caused by simultaneous action of a dynamic Jahn-Teller effect and random strains. Both these centres show isotropic hyperfine structure with 12 equivalent next-nearest Cd neighbours, proving that the Ti impurity substitutes for Cd at lattice sites of Td symmetry. The EPR signals are photosensitive in the visible and near-infrared regions. The luminescence spectra of Ti centres in Cd1-xZnxTe:Ti with x = 0.15 show the 3T2(F) 3A2(F) transition of Ti2+ centred at 2 600 cm-1 and the 2E(D) emission of Ti3+ around 3200 cm-1. The excitation spectrum of the Ti2+ luminescence shows three excitation bands, viz. to 3T1(F), 3T1(P), and near-gap levels.
