DLTS of silver in germanium: evidence for an amphoteric impurity

Abstract

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.

Electronic properties of titanium and chromium impurity centers in germanium

“…7,16,17 The spectrum of Cr, with triple acceptor levels and a very deep donor level, resembles the cases of Ag and Au. 7,18,19 For the latter metals with d 10 s 1 configuration, the triple acceptor activity has been qualitatively explained by a tetrahedral bonding model for the substitutional impurity. 1 The argument is less straightforward for the transition metals with a par-tially filled d-shell, although in the cases mentioned above a similar correspondence exists between the acceptor multiplicity and the 4s occupation, i.e., a double acceptor for a 4s 2 configuration ͑Ti͒ and a triple acceptor in the case of a 4s 1 configuration ͑Cr͒.…”

Electronic structure and Jahn–Teller instabilities in a single vacancy in Ge

“…This method was shown to predict levels with an error bar of ∼0.2 eV, but when the marker and the defect under scrutiny possess electron states which are similar in symmetry and extent, deviations from the measurements fall below 0.1 eV [21]. For donor markers, we have chosen substitutional sulfur (E c − E(0/+) = 0.28 eV and E c − E(+/++) = 0.59 eV) [22], selenium (E c − E(0/+) = 0.27 eV and E c − E(+/++) = 0.51 eV) [22], silver and gold (E(0/+) − E v = 0.035 eV and E(0/+) − E v = 0.044 eV, respectively) [23,24]. For acceptor markers, substitutional silver (E(−/0) − E v = 0.116 eV, E c − E(=/−) = 0.261 eV and E c − E(≡/=) = 0.113 eV) [23], and substitutional gold (E(−/0) − E v = 0.135 eV, E c − E(=/−) = 0.215 eV and E c − E(≡/=) = 0.056 eV) [24], were adopted.…”

“…For donor markers, we have chosen substitutional sulfur (E c − E(0/+) = 0.28 eV and E c − E(+/++) = 0.59 eV) [22], selenium (E c − E(0/+) = 0.27 eV and E c − E(+/++) = 0.51 eV) [22], silver and gold (E(0/+) − E v = 0.035 eV and E(0/+) − E v = 0.044 eV, respectively) [23,24]. For acceptor markers, substitutional silver (E(−/0) − E v = 0.116 eV, E c − E(=/−) = 0.261 eV and E c − E(≡/=) = 0.113 eV) [23], and substitutional gold (E(−/0) − E v = 0.135 eV, E c − E(=/−) = 0.215 eV and E c − E(≡/=) = 0.056 eV) [24], were adopted. The 4d and 5d shells on Au and Ag, respectively, were explicitly treated as valence states.…”