GaN hot electron transistors: From ballistic to coherent

Abstract

Previously we demonstrated high-current, high-gain III-nitride hot electron transistors (HETs) with collimated electron injection into an undoped base region, reaching collector current density of ∼0.44 MA/cm2 and Gummel gain β ∼ 2 at 300 K. Here, we compare the behavior of these devices from 300 to 77 and 4.2 K to elucidate the role of hot electron scattering in limiting the performance. Under cryogenic operation and Gummel biasing, we obtain a maximum current gain of 3.5 at a collector current density of 1.35 MA/cm2, limited by the onset of intervalley electron transfer, and common-emitter current gain β > 20. Our results point to the promise of nitride HETs for realizing the long-proposed coherent transistor.