Work-function engineering in novel high Al composition Al0.72Ga0.28N/AlN/GaN HEMTs

Abstract

Enormous progress has been made in low Al composition (<40 %) AlGaN/GaN HEMTs for high power and high frequency applications [1]. For scaling down to deep sub-micrometer dimensions, high Al composition AlGaN barrier can offer higher two-dimensional electron gas (2DEG) density and lower sheet resistance than low Al composition AlGaN [2]. Pure AlN barriers cause high contact resistance due to their wide band gap (6.2 eV) [3]. Compared to lattice-matched AlInN barriers, the higher band gap and conduction band offset of high Al composition AlGaN barrier can result in lower gate tunneling current [4]. In this work we report the device characteristics of novel high Al composition Al0.72Ga0.28N/AlN/GaN HEMTs. By combining ALD technology, threshold voltage control by work-function engineering is demonstrated for the first time.