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

• Published in: Applied physics letters 2016-11, Vol.109 (22)
• Main Authors: Armstrong, Andrew M., Allerman, Andrew A.
• Format: Article
• Language: English
• Subjects: Aluminum gallium nitrides; Applied physics; Band gap; Composition; Electric potential; Electrical resistivity; Electron mobility; Electronic devices; Energy gap; Epitaxial growth; Evaluation; Field effect transistors; High voltages; Metalorganic chemical vapor deposition; Polarization; Schottky diodes; Semiconductor devices; Ultrawideband; Vapor phase epitaxy
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4969062

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.