QUANTUM INTERFERENCE AND SPILL EFFECTS IN THE VARIABLE-RANGE-HOPPING MAGNETORESISTANCE OF HEAVILY-DOPED SEMICONDUCTORS - COMPARISON BETWEENSI, GE, CDTE AND GAAS

The negative hopping magnetoresistance (NHM) due to quantum interferen ce, asm;ell as the positive hopping magnetoresistance (PHM) due to til e reduced overlap between the impurity wave functions should both only increase as tile temperature decreases. For the first time in GaAs, C dTe and Ge we observed with decreasing temperatures a more complicated dependence on temperature and magnetic field. Tile NHM initially incr eases with decreasing temperature bu?; then decreases sharply, and dis appears at tile lowest temperature. We relate this Effect to the spin alignment of the impurity atoms in the magnetic field for g mu much g reater than k(B)T. Experimentally this new spin contribution depends s trongly on the impurity concentration which; together with tile critic al concentration of the MIT, increases in the sequence of GaAs, CdTe, Ge, Si from 2 x 10(16) to 3.5 x 10(18) cm(-3). The small NHM in Ge and its absence in Si may be due to dominating spin effects.