Compensating defects in high Al content Al0.85Ga0.15N films grown on an AlN substrate

AlxGa1-xN is a promising semiconductor for power electronics, but the mechanism for the conductivity produced by Si doping is controversial. In this work, temperature-dependent Hall measurements were conducted to address the conduction mechanism and electron paramagnetic resonance (EPR) was used to observe the Si dopant and other point defects. The samples studied were 0.5 um thick Al0.85Ga0.15N films grown by molecular beam epitaxy on a 1 um AlN film on an AlN substrate. The results reveal a nearly temperature independent carrier density, suggesting impurity band conduction. Notably, 1019 cm−3 carriers were detected at room temperature, despite the presence of several defects detected by EPR. The centers include the neutral donor with DX character and a second center, with as-yet undetermined origin, that likely partially compensates the Si donors during growth. The minimal effect of the unintentional defects and DX-character of the dopant is reasoned to be due to 1) the small energy barrier between the donor and DX level and 2) the low density (1017 cm−3) of the unintentional defects. Thus, although the growth of high Al content AlGaN may incur unwanted defects and the Si dopant may be a DX center, usefully high carrier concentrations may be achieved.