Electron configuration and charge state of electrically active Cu, Ag and Au ions inZnSe

Abstract

The Hall effect, electrical conductivity and electron mobility are investigated attemperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. Thepresence of a small amount of Cu atoms leads to an inversion of the sign of the Hallcoefficient at temperatures above 300 K. Anomalous temperature dependenceof the electron mobility is observed in the samples with low Cu concentration(<0.3 at.% in the melt). Different characters of the temperature dependences of kineticcoefficients are found for n-ZnSe doped with Ag and Au. These curves are typical forcrystals having several donor levels at different energetic depths. Immediately afterdoping, silver behaves like a usual compensating acceptor impurity while gold showsamphoteric properties. We propose a model that explains the anomalies of thetemperature dependences of the kinetic coefficients in Cu-doped crystals and thelack of the anomalies in Ag-doped and Au-doped crystals. In accordance withthis model and our experimental data, copper in n-ZnSe has two charge states,CuZn+ (d10)and CuZn2+ (d9), and two acceptor levels near the valence band. Silver and gold exist in single-charged statesAgZn+ and AuZn+ with d10 electron configuration forming single energy levels near the valence band. Au atoms form mainly interstitialAui donors at low doping concentrations and substitutionalAuZn and AuZn-based acceptors at high doping concentrations. Time stimulation of the amphotericproperties of Ag is discussed.