Experimental and Theoretical Piezospectroscopy of Neutral Copper Impurity in Germanium.

A group-theoretical study of triple acceptors in group-IV semi-conductors under an applied uniaxial force, F,(' )has been made employing the self-consistent-field model. The ground state, constructed from three equivalent single-hold (GAMMA)(,8) states, is found to be itself a (GAMMA)(,8) state, whereas the excited states are more complex. The energy splitting of the various impurity states and the relative intensities of the associated stress -induced components have been determined for F(' )(PARLL) <100>, <111> and <110>. Only effects linear in stress have been considered. The optical absorption spectrum of the group-I impurity, neutral copper, in germanium at liquid helium temperature and above has been studied using photon energies near 40 meV and quantitative uniaxial compression with polarized radiation for F(' )(PARLL) <100>, <111> and <110>. The piezospectroscopic behaviour of this triple acceptor is found to be surprisingly simple and very similar to those of single acceptors. However, several discrepancies cannot be explained within the self-consistent-field model. The deformation potential constants for the various states have been obtained along with the intensity parameters of the D line.