RECENT PROGRESS ON GaN-BASED ELECTRON DEVICES

Abstract

We present results of some novel AlGaN/GaN heterojunction field-effect transistors (HFETs) specifically developed for RF front-end and power applications. To reduce the parasitic resistance, two unique techniques: selective Si doping into contact area and a superlattice (SL) cap structure, are developed. With the selective Si doping method, a transistor with an on-state resistance as low as 1.86 Ω·mm and a Tx/Rx switch IC with very low insertion loss (0.26 dB) and very high power handling capability (P1dB over 40 dBm) were obtained. With the SL cap HFETs, an ultra low source resistance of 0.4 Ω·mm was achieved and excellent DC and RF performances were demonstrated. The typical characteristics of these HFETs are: maximum transconductance of over 400 mS/mm, maximum drain current of 1.2 A/mm, cut-off frequency of 60 GHz, maximum oscillation frequency of 140 GHz, and a very low noise figure of 0.7 dB with 15 dB gain at 12 GHz. For power applications, in order to significantly reduce fabrication cost, we fabricated the AlGaN/GaN HFET on a conductive Si substrate with a source-via grounding (SVG) structure. The device has a very low on-state sheet resistance of 1.9 mΩ·cm2, a high off-state breakdown voltage of 350 V, and a current handling capability of 150 A. In addition, a sub-nano second switching response with t r of 98 ps and t f of 96 ps with a current density as high as 2.0 kA/cm2 is demonstrated for the first time.