Growth and fabrication of GaN/AlGaN heterojunction bipolar transistor

Abstract

A GaN/AlGaN heterojunction bipolar transistor structure with Mg doping in the base and Si doping in the emitter and collector regions was grown by metalorganic chemical vapor deposition on c-axis Al2O3. Secondary ion mass spectrometry measurements showed no increase in the O concentration (2–3×1018 cm−3) in the AlGaN emitter and fairly low levels of C (∼4–5×1017 cm−3) throughout the structure. Due to the nonohmic behavior of the base contact at room temperature, the current gain of large area (∼90 μm diameter) devices was <3. Increasing the device operating temperature led to higher ionization fractions of the Mg acceptors in the base, and current gains of ∼10 were obtained at 300 °C.