DLTS results of the third acceptor level of substitutional copper in n-type germanium are presented for the first time. Accurate determination of the signature and the temperature dependence of the electron capture cross section yields an energy level of E, -0.26 eV in agreement with the Hall effect. It is shown that two DLTS bands attributed in the literature to the third copper level should correspond to other defects.

The band-gap levels introduced by gold in germanium have been investigated using DLTS. The samples were taken from well characterised n-and ptype germanium crystals and were doped with gold by diffusion at 7 0 0 OC followed by a quench to room temperature. Three acceptor levels at E, -0.056 eV, E, -0.2 15 eV and E , + 0.1 35 eV and one donor level at E, + 0.044 eV are observed, in agreement with published data obtained from Hall effect studies. All four levels are attributed to one amphoteric defect, i.e. the gold substitutional.

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The defect parameters of substitutional silver in germanium have been investigated with DLTS. Silver, when diffused into germanium, introduces four occupancy levels in the band gap. Three of them are already known from Hall experiments: the acceptor levels with ionisation enthalpies €,+0.116 eV, E,-0.261 eV and E,-0.1 13 eV. The fourth level, a very deep donor situated at €,+0.035 eV, has never been reported before. This new level implies that silver is the third known amphoteric impurity in germanium, besides gold and cobalt.

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