Metals in germanium

An overview of the present knowledge of the electronic properties of Ib metals and transition metals in germanium is given. Similar impurities introduce deep-level states in the bandgap and may be active as recombination centres or carrier traps, even at low concentration. Those metals are also among the fastest diffusers which means that they are easily introduced during processing involving thermal treatments. Early data obtained by Hall effect are compared with more recent results from deep-level transient spectroscopy (DLTS), which is more suitable in the context of processing. Complete identification of the electronic levels of substitutional Cu, Ag, Au and Ni has been obtained; however, for many other metals the results are still incomplete or could not be confirmed. The latter is due to low solubility and contamination by unwanted impurities like Cu and Ni during metal diffusion. Estimates are also presented of the effect of transition metals on the minority carrier lifetime.