Photoionization of Ge¯-DX State in GaAs

We have determined the efficiency of photoionization of Ge¯-DX state in GaAs as a function of photon energy. The optical ionization energy derived from the fitting is about 1.0 eV. It proves a large difference between optical and thermal ionization energies and confirms that for Ge-impurity, the broken-bond model and large lattice relaxation are valid and not the breathing mode with small lattice relaxation, resulting from the calculations presented for Ge-impurity in T.M. Schmidt, A. Fazzio, M.J. Caldas, Mater. Sci. Forum 196/201, 273 (1995).