EFFECT OF THE COULOMB INTERACTION ON THE THERMAL IONIZATION-ENERGY OFTHE DOMINANT IMPURITY IN COMPENSATED GE-GA

The role of the Coulomb interaction in the thermal ionization of the g round state of the dominant impurity in a compensated semiconductor wa s investigated experimentally using a series of neutron-doped Ge:Ga sa mples with a degree of compensation K=0.3. The thermal ionization ener gy epsilon(1) was determined from the exponential temperature dependen ces of the Hall coefficient in the region of classical transport of eq uilibrium holes, produced by thermal ionization of the ground state of Ga, along the valence band. It was shown that in the region of light doping N<10(15) cm(-3)=0.01N(C), where N-C is the critical Ga concentr ation in Ge for a metal-insulator transition, the dependence of epsilo n(1), on the compensation and the degree of doping are described by th e Uzakov-Efros model. The well-known fact that epsilon(1) decreases wi th increasing doping is explained by the relaxation of the charge stat e of the impurity band in each thermal-ionization event (the electroni c analog of the Franck-Condon principle). For intermediate degrees of doping 0.01N(C)<N<0.1N(C) the Lien-Shklovskii model was found to be va lid. This model attributes the change in epsilon(1)(N, K) to the diffe rence in the motion of the energies of the Fermi level and the percola tion level. (C) 1995 American Institute of Physics.