The last decades germanium is regaining importance as active layer in semiconductor technology because of the high (drift) mobility of carriers. Most of the interesting properties of this material stem from impurities and point defects.
Some of these impurities (f.e. transition metals) give rise to deep levels in the band gap, which can reduce the carrier lifetime and therefor need to be studied. Due to its high sensitivity, deep level transient spectroscopy (DLTS) is an excellent technique to detect and identify these impurities and defects.
In this work, p-type germanium wafers have been quenched or intentionally contaminated with transition metals and studied by DLTS. At low temperatures, a quasi-constant emission component has been observed at high time windows (oder of seconds). This component can be associated with a tunneling emission of holes from a defect state towards the valence band. By considering a single quantum well and using the model proposed by Letartre et al. [1], experimental evidence of this tunneling effect in germanium will be given and the electrical properties of these defects will be examined.
[1] X. Letartre, D. Stiévenard, M. Lannoo and E. Barbier, J. Appl. Phys. 69, 7336 (1991
