ENERGY-GAP BETWEEN THE CONDUCTION-BAND AND THE UPPER HUBBARD BAND

The behavior of the energy gap epsilon between the bottom of the condu ction band and the upper Hubbard band has been studied over the wide d oping range 0.07 less-than-or-equal-to N1/3 a less-than-or-equal-to 0. 25, where N is the dopant concentration, and a is the carrier localiza tion length at an impurity. At N1/3 a less-than-or-equal-to 0.12, the experimental values of epsilon(N) agree with values calculated from Ni shimura's theory.