Bias Stress Measurements on High Performance AlGaN/GaN HFET Devices

Abstract

High performance AlGaN/GaN heterojunction field effect transistor (HFET) devices have been fabricated, using material grown by MBE on sapphire substrates. The Hall effect 2DEG sheet charge densities and mobilities were as high as 1.68 Â 10 13 cm --2 and 1000 cm 2 /Vs respectively. Peak dc currents in excess of 1 A/mm, with transconductances in excess of 220 mS/mm were common. f T and f max scaled linearly with the inverse of the gate length, with maximum values of 39 and 80 GHz recorded for T-gates of length %0.3 mm. The devices with optically defined gates were stressed at V DS = 10 V and V G = 1 V, for times up to 5000 s. The stress decreased both f T and f max , but this degradation mostly recovered after a few days. In contrast, the gate leakage current improved (decreased) with stressing, but did not return to the initial undesirable levels. Thus, we found that electrical bias stressing can have a positive effect on some of the characteristics of our devices.

Al-Free Nanolayered Metallization Systems for Sub-Micron HEMTs

“…Among the variety of ohmic contacts proposed for HEMTs [6], most of the metallization schemes are based on Al [7][8][9][10][11][12][13][14][15][16][17] because of its low work function (4.06 eV). However, due to the tendency of the aluminium to ball at high temperatures, these contacts have rough surface and bad edge acuity.…”