Quasiclassical Anderson transition and thermally activated percolative charge transport in single-crystalline ScN

Quasiclassical Anderson transition (QAT) represents the crossover from metallic to activated conduction in heavily doped highly compensated semiconductors (HDHCSs) due to large-scale potential fluctuations. The spatial inhomogeneity of the charged dopants in HDHCSs localizes carriers, forming metallic droplets surrounded by potential barriers. Nitride semiconductors are seldom explored for HDHCS studies due to the difficulty in synthesizing stoichiometric high-quality films and self-compensation effects. Here we show conclusive experimental evidence of the QAT in compensated scandium nitride (ScN) single-crystalline films. Mg (hole) doping in $n$-type ScN increases the resistivity by nine orders and leads to semi-insulating films exhibiting a distinct crossover from the hopping conduction at low temperatures to thermally activated percolative transport at high temperature. The sign reversal of the Seebeck coefficient, anomalously low Hall mobility that increases with raising temperature, and persistent photoconductivity support the QAT and carrier transport mechanisms. QAT in single-crystalline nitrides could lead to lattice-matched devices with lasers, modulators, and dynamic holographic applications.