Effects of Doping, Disorder, and Compensation on Electron Conduction in Si‐Doped k-Ga2O3 Close to the Metal‐to‐Insulator Transition

Si-doped κ-Ga2O3 epilayers grown by metal–organic vapor phase epitaxy on c-oriented sapphire were investigated by temperature-dependent resistivity, Hall measurements, electron-paramagnetic resonance (EPR), high-resolution transmission electron microscopy (TEM), and elastic-recoil detection analysis (ERDA). The electrical properties were found consistent with variable-range hopping transport (VRH) through localized states, with the electronic system persisting on the insulating side of a metal-to-insulator transition for any silane flow used. The physical meaning of Hall voltage under hopping transport was critically discussed through the comparison with EPR results. The electronic properties of the samples were described considering the high density of structural defects detected by TEM, hydrogen incorporation found by ERDA, ab-initio calculations, reconciling all results with current literature and with VRH parameters extracted from resistivity data analysis. The conclusion is that most of the Si incorporated in the layers is (self-)compensated, with a compensation ratio higher than 0.9 inhibiting the transition to metal conduction. Structural defects, such as boundaries between rotational domains and off-plane planar antiphase boundaries, are proposed to play a pivotal role in such high compensation via formation of doping-dependent point defects and related deep levels. The role of significant hydrogen incorporation in deep acceptor passivation and compensation reduction is discussed.