Nonpolar (11-20) plane AlGaN∕GaN heterojunction field effect transistors on (1-102) plane sapphire

Abstract

GaN-based compound semiconductors have been investigated for use in future power switching devices with high breakdown voltages and low on-state resistances due to their high breakdown field and high saturation electron velocity. To date, conventional AlGaN∕GaN heterojunction field effect transistors (HFETs) are fabricated on c-plane across which the spontaneous and piezoelectric polarization fields produce extraordinarily high sheet carrier concentrations. In this paper, we report on the epitaxial growth and fabrication of AlGaN∕GaN HFETs on (11-20) a-plane which are not affected by the polarization fields. The a-plane’s epitaxial layers are grown on (1-102) r-plane sapphire substrates by metal organic chemical vapor deposition. The sheet carrier concentrations can be controlled by simply doping the AlGaN in the nonpolar devices. The a-plane devices exhibit nearly normally-off characteristics in which the threshold voltage is −0.5V, while that of the conventional c-plane device is −4.0V. The HFET on nonpolar planes easily enables normally-off operation which is highly desirable in power switching applications.