Conductivity and Hall-effect in highly resistive GaN layers

Abstract

Highly resistive GaN layers grown by molecular beam epitaxy are characterized by temperature dependent conductivity and Hall effect measurements. Samples with ρ300≅3×103 Ω cm show room temperature Hall mobility of 22 and 35 cm2 V−1 s−1 and have a temperature dependence μH∼Tx with x=0.9 and 0.5. This is in contradiction to a sample with ρ300≅32 Ω cm which has a room temperature mobility of 310 cm2 V−1 s−1 and a μH∼Tx with x=−1.4. The same activation energy of 0.23 eV, attributed to donor-like defects, is found for all three samples investigated. Temperature dependent conductivity data can be reasonably fitted considering band conduction. The presence of various hopping mechanisms is discussed.