Polarization-induced electrical conductivity in ultra-wide band gap AlGaN alloys

摘要

Unintentionally doped (UID) AlGaN epilayers graded over Al compositions of 80%-90% and 80%-100% were grown by metal organic vapor phase epitaxy and were electrically characterized using contactless sheet resistance (R_(sh)) and capacitance-voltage (C-V) measurements. Strong electrical conductivity in the UID graded AIGaN epilayers resulted from polarization-induced doping and was verified by the low resistivity of 0.04 Ω cm for the AlGaN epilayer graded over 80%-100% Al mole fraction. A free electron concentration (n) of 4.8 × 10~(17)cm~(-3) was measured by C-V for Al compositions of 80%-100%. Average electron mobility (anti mu) was calculated from R_(sh) and n data for three ranges of Al composition grading, and it was found that UID AlGaN graded from 88%-96% had anti mu = 509 cm~2/V s. The combination of very large band gap energy, high anti mu, and high n for UID graded AlGaN epilayers make them attractive as a building block for high voltage power electronic devices such as Schottky diodes and field effect transistors.