Interpretation of the Temperature‐Dependent Transport Properties of GaN/Sapphire Films Grown by MBE and MOCVD

Electron transport in Si‐doped and unintentionally‐doped GaN films grown on sapphire by MOCVD and MBE has been analysed assuming that a parallel conducting channel, via an impurity band, is present. No dependence on growth method or dopant type was observed, but other trends were apparent: a) the activation energy for the impurity band fell with increased doping; b) the temperature of the minimum in the Hall carrier density versus temperature curves increased with doping, but did not depend strongly on the absolute value of mobility; c) the ratio of the mobility in the GaN conduction band to that in the impurity band also showed systematic behaviour, possibly arising from structure‐related scattering processes. An STM study of the surface characteristics of some of these samples suggests that potential variations associated with particular structural features may be important in influencing the electrical properties.