Low temperature transport of n-type gallium nitride

We measured the electrical conductivity of 1-2 /spl mu/m thick n-type intentionally and unintentionally doped gallium nitride samples from 1.5 to 290 K. Room-temperature Hall measurements show carrier densities in the range of 6.6/spl times/10/sup 16/ to 3.7/spl times/10/sup 18/ cm/sup -3/, and mobility values from 543 to 261 cm/sup 2//V-sec over this carrier density range. Hopping is among impurity sites, and the hopping distance increases with decreasing doping concentration for the silicon-doped samples.