The electronic properties of defects resulting from electron irradiation of Ge at low temperatures were investigated. Various space-charge capacitance-transient spectroscopy techniques connected with an electron-beam facility were applied. In n-type Ge, a level at about 0.14eV was identified below the conduction band whose properties resembled those of a defect previously attributed to a close vacancy-interstitial or Frenkel pair. This pair seemed to annihilate over a small barrier at about 70K, and its stability was particularly sensitive to the irradiation temperature and energy. Two coupled levels were also observed at 0.08 and 0.24eV below the conduction band; stable up to 160K. Recent independent theoretical work had predicted the existence of the single and double donor of the Ge interstitial with energy levels matching these 2 values exactly. These tentative identifications constituted a major difference with respect to Si, where neither the Frenkel pair nor self-interstitial had ever been detected. Two levels were found in p-type Ge. The shallower one, located at about 0.14eV above the valence band, was tentatively attributed to the vacancy. It exhibited a field-driven instability at about 80K, which made its analysis difficult. The application of a reverse bias led to a strong drift process which swept this defect out of the observation area without necessarily annealing it out. Unlike the case of Si, where the vacancy had 4 charge states, only one vacancy-related level appeared to exist in Ge, and was probably a double acceptor. One hole mid-gap trap behaved much like the B interstitial in Si. This led to the suggestion that it might arise from the Ga interstitial, which was a naturally occurring dopant in these Ge samples. Such a situation would reflect operation of the Watkins replacement mechanism in Ge.

Low-Temperature Irradiation-Induced Defects in Germanium - in situ Analysis. A.Mesli, L.Dobaczewski, K.Bonde Nielsen, V.Kolkovsky, M.C.Petersen, A.Nylandsted Larsen: Physical Review B, 2008, 78[16], 165202 (16pp)