Irradiation was carried out at 77, 300, and again at 77K. The use of extended doses during final irradiation at 77K revealed the presence of a defect center which absorbed at 3400/cm. This increased linearly with accumulated radiation dose. Another small band was observed at 3602/cm in quickly grown samples. A Ge-doped crystal which had been grown under high pressures, and a Premium-Q crystal, did not exhibit either of these bands. Whereas irradiation at 300K produced Al-OH- bands in all of the samples, their strength was increased in comparison with the as-received material in the case of crystals which were grown under a high pressure. Isochronal annealing showed that the low-temperature irradiation-induced band at 3400/cm remained constant at 120 to 180K, and decayed sharply to about 15% of its maximum strength at 180 to 200K. The depletion of this band coincided with the onset of recovery of the usual growth defect bands, together with an increase in the 3602/cm band within this temperature range. This showed that the defect centers which absorbed at 3602 and 3400/cm arose from an interrelated configuration of hydroxyl point defects. The 3400/cm radiation-induced band was attributed to a Ge-H-Li complex of the form, [Ge4+e-M+e-H+]0.

H.Bahadur: Physical Review B, 1995, 52[10], 7065-75