Silicon doping dependence of highly conductive n-type Al0.7Ga0.3N

Highly conductive Si-doped n-type Al0.7Ga0.3N alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. Variable temperature Hall-effect measurements have been employed to study the electrical properties for samples with nominal Si dopant concentration (NSi) from 2.6 to 6.8×1019cm−3. For the sample with NSi=6.0×1019cm−3, we have achieved n-type resistivity of 0.0075Ωcm with an electron concentration of 3.3×1019cm−3 and mobility of 25cm2∕Vs at room temperature. For the same sample, the effective donor (Si) activation energy E0 was determined to be as low as 10meV. E0 increases to 25meV as NSi is reduced to 2.6×1019cm−3, which can be explained by the bandgap renormalization effect. This implies that heavy doping is necessary in high-Al-content AlGaN alloys to bring down the donor activation energy, therefore a higher conductivity.