Far-infrared photoconductivity spectra of quenched-in acceptors in Germanium: absorption and photo-thermal ionization lines of two new shallow acceptors

Abstract

The far-infrared photoconductivity spectra of germanium crystals quenched from T>800C show three new sets of hydrogenic acceptor excitation lines, in addition to the 8.69 meV (SA ' 1) and 9.48 meV (SA “ 1) acceptor series reported earlier. The corresponding ground state binding energies are 13.89 meV (SA ' 2), 14.42 meV (SA “ 2), and 17.89 meV (SA 3). We tentatively attribute both the SA ' 2 and the SA “ 2 line series to one acceptor complex with a multiple ground state. At high acceptor concentrations the excitation lines are seen as sharp minima superimposed on a continuous photoconductivity background. With decreasing acceptor concentration, or increasing temperature, they gradually evolve into the familiar positive-going photo-thermal ionization peaks. This is explained by the different concentration and temperature dependence of the cross-sections for the absorption and photo-thermal ionization mechanisms.