Conduction mechanism and shallow donor properties in silicon-doped ε-Ga2O3 thin films: An electron paramagnetic resonance study

The defects in Si-doped epsilon-Ga2O3 epitaxial layers have been investigated by electron paramagnetic resonance (EPR) spectroscopy. The results show that Si doping introduces a single, paramagnetic defect, attributed to Si incorporation on the tetrahedral gallium lattice site. It is a spin S = 1/2 center with an axial g tensor with principal values of g//c = 1.9573 and g perpendicular to c = 1.9591. The temperature dependence of the EPR parameter demonstrates that it is a shallow effective mass donor, which is at the origin of the n-type conductivity. The EPR spectrum is modified by motional narrowing effects, the analysis of which allows one to reveal different transport regimes, including localization, hopping conductivity, and ionization in the conduction band when the temperature is raised from T = 4 K to room temperature. Partial electrical compensation and donor clustering are equally evidenced by the EPR results, which are confirmed by correlated electrical transport measurements. Silicon is thus a promising dopant for the formation of highly conductive n-type epsilon-Ga2O3.