Electron mobility exceeding 104 cm2/V s in an AlGaN–GaN heterostructure grown on a sapphire substrate

High-quality AlGaN/GaN undoped single heterostructures (SH) with different Al contents have been grown on sapphire substrates. The magnetotransport investigation was performed on these samples at a low temperature. The observation of Shubnikov–de Hass oscillations in the magnetic fields below 3 T and the integer quantum Hall effect confirmed the existence of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. The ${\mathrm{Al}}_{\mathrm{0.18}}{\mathrm{Ga}}_{\mathrm{0.82}}\mathrm{N/GaN}$ SH shows a Hall mobility of 10 300 cm²/V s at a carrier sheet density of ${\text{6.19×10}}^{12}/{\mathrm{cm}}^{\mathrm{2}}$ measured at 1.5 K. To the best of our knowledge, this is the highest carrier mobility ever measured in GaN-based semiconductors grown on sapphire substrates. The Al composition dependence of the mobility and carrier sheet density were also investigated. Based on the piezoelectric field effect, the Al composition dependence of the 2DEG sheet density was calculated, which agreed well with the experimental result. The negative magnetoresistance with parabolic magnetic-field dependence in the low magnetic field was also observed in the sample with the highest 2DEG sheet density.