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

Abstract

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 (Rsh) and capacitance-voltage (C–V) measurements. Strong electrical conductivity in the UID graded AlGaN 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 × 1017 cm−3 was measured by C–V for Al compositions of 80%–100%. Average electron mobility (μ¯) was calculated from Rsh and n data for three ranges of Al composition grading, and it was found that UID AlGaN graded from 88%–96% had μ¯ = 509 cm2/V s. The combination of very large band gap energy, high μ¯, 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.