High-resolution local vibrational mode spectroscopy of the negatively charged oxygen–vacancy complex in germanium

Abstract

It was recently discovered that in irradiated germanium doped with oxygen a local vibrational mode occurs at 669cm−1 which could be ascribed to the negatively charged oxygen–vacancy (VO−) complex. In the 669cm−1 band and in another band at 731cm−1 due to a different defect, fine structure which indicated the occurrence of the Ge-isotope splitting of the modes could be partly resolved. We report here the results of high-resolution infrared measurements (res.=0.02cm−1) at liquid helium temperatures of the two bands. The oxygen-doped germanium ([Oi]=2.7×1017cm−3) was first irradiated with 2MeV electrons to increase the concentration of VO complexes. A second similar specimen received the same treatment but with subsequent anneals to obtain the 731cm−1 band. The experimentally observed splitting of the 669cm−1 band and the amplitudes of its individual components are accurately predicted using a model of a non-linear symmetric Ge–O–Ge molecule within a Ge crystal lattice, in agreement with the assignment of the mode to the VO− complex. A similar model also seems to apply to the yet unassigned 731cm−1 mode and the conclusion is made that the defect also must include a single O atom bonded to two equivalent Ge atoms. The higher annealing temperature of the unassigned band however indicates that the defect must be more complex than the VO center.