An Investigation into the Mechanisms of Electron Transport in Highly Doped Al_XGa_1-XN:Si (X > 0.65)

Al_XGa_1-XN, as an ultra-wide bandgap semiconductor (5-6 eV), is a promising material for UV-LEDs and high-power electronics, but ineffective doping for conduction has proven to be a prominent barrier for industrial implementation. Existing literature shows an increase in activation energy for conduction with increasing aluminum mole fraction, thus making highly conducting AlGaN components a challenge. Compensating defects are believed to be the cause, specifically those with a negatively correlated energy referred to as DX^- centers. The goal of this research is therefore to develop a better understanding of the mechanism of electron transport within highly silicon doped Al_XGa_1-XN (X > 0.65), specifically by monitoring the neutral donor concentration and linewidth with 10 GHz electron paramagnetic resonance (EPR). Samples were doped with Si on the order of 10¹⁸ – 10²⁰ [cm^-3] and were measured from room temperature to 4K. The temperature dependence of the neutral donor EPR spectra linewidth and intensity were measured, and statistical models were used to understand the mechanism of transport in these high Al mole fraction AlGaN samples. The results of this research indicate the presence of impurity band conduction and electron hopping. Temperature dependent EPR intensity also hints at possible DX behavior.