chapter  13
30 Pages


AlGaN/GaN high electron mobility transistors (HEMTs) have great potentials in wireless communications and radar applications. However, the current leakage in conventional Schottky gate GaN electronic devices is a major hindrance. A degradation of critical device properties such as the breakdown voltage, efficiency, and gain is induced by the large reverse leakage current of the Schottky gate AlGaN/GaN HEMTs, due not only to the high-density dislocations in GaN, especially those penetrating to the material surface, but also to the constant high electric field and junction temperature to which GaN HEMT devices are exposed whether in microwave power or power switching applications. Besides the reverse leakage current, the forward gate conduction may occur in the Schottky gate AlGaN/GaN HEMT at a relatively large forward bias (>2V), in which case the device may fail. As a result, the Schottky gate cannot meet the requirements of enhancement-mode GaN devices typically operating at a large positive bias, since such high gate currents driven by the radio frequency (RF) signals lead to reduced breakdown voltage and PAE as well as an increased noise figure of the AlGaN/GaN HEMTs and affect the reliability of long-term operation of the device (Winslow and Trew 1994).