ELECTRON-TRANSPORT MECHANISM IN GALLIUM NITRIDE

The electron transport mechanism in autodoped gallium nitride films grown by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy was investigated by studying the temperature dependence of the Hall coefficient and resistivity on samples with various concentrations of autodoping centers. The Hall coefficients go through a maximum as the temperature is lowered from 300 K and then saturate at lower temperatures. The resistivities in the same temperature range initially increase exponentially and then saturate at lower temperatures. These findings are accounted for if a significant fraction of electron transport, even at room temperature, takes place in the autodoping centers and that conduction through these centers becomes dominant at lower temperatures. The activation energy of these centers was found to be on the order of 20-30 meV. When the concentration of the autodoping centers becomes smaller than that of deep compensating defects, the material becomes semi-insulating and transport by hopping in the compensating defects becomes dominant.