ELECTRON-CONCENTRATION DEPENDENCE OF THE COULOMB GAP IN ALGAAS-SI

The Efros-Shklovskii (ES) T-1/2 and Mott T-1/4 parameters and the widt h of the soft Coulomb gap in Al0.3Ga0.7As:Si have been determined for electron concentration n ranging from 1.2 x 10(16) to 14 x 10(16) cm(- 3). The gap width presents a maximum at an n value corresponding to a compensation ratio K between 0.94 and 0.97. The T-1/2 and T-1/4 parame ters decrease exponentially with II and provide the simple relation e( 2)g(0) xi(2)/kappa proportional to n, between the localization length xi and the dielectric constant kappa. This is compatible with scaling theory. Our data also suggest that the validity limits for the Mott an d ES regimes should be estimated, respectively, by 2.5(T-1/2)(2)/T-1/4 and (T-1/2)(2)/T-1/4. [S0031-9007(98)05315-0].