Localization Effects in a Non-Degenerate 2D Electron Gas

We have measured the magnetoresistance of a 2D electron gas on a solid hydrogen substrate as a function of the surface disorder. Very clean crystal surfaces give rise to large electron mobilities and an essentially classical positive magnetoresistance. For sufficiently low mobility surfaces, however, a negative contribution to the magnetoresistance appears in the region below ~ 1 kG. This effect is quite similar to that observed in the inversion layer fo Si MOSFET systems and is, we believe, strong evidence for localization in a "classical" electron gas. In contrast to degenerate systems, the coherent backscattering correction to the conductivity for a Boltzman distribution scales as n where n is the electron density and T is temperature.