Compositionally graded contact layers for MOCVD grown high Al-content AlGaN transistors

TL;DR

This paper presents a novel graded contact layer for MOCVD-grown high Al-content AlGaN transistors, significantly reducing contact resistance and enhancing device performance in ultra-wide bandgap applications.

Contribution

It introduces an improved reverse Al-composition graded contact layer that achieves lower resistance and better device metrics in high Al-content AlGaN transistors.

Findings

Contact resistance reduced to 3.3x10^-5 Ohm.cm2

Maximum current density of 635 mA/mm at VGS=+2 V

Breakdown voltage exceeds 220 V with a field of 2.86 MV/cm

Abstract

In this letter, we design and demonstrate an improved MOCVD grown reverse Al-composition graded contact layer to achieve low resistance contact to MOCVD grown ultra-wide bandgap (UWBG) Al0.70Ga0.30N channel metal semiconductor field-effect transistors (MESFETs). Increasing the thickness of the reverse graded layer was found to improve contact layer resistance significantly, leading to contact resistance of 3.3x10^-5 Ohm.cm2. Devices with gate length, LG, of 0.6 microns and source-drain spacing, LSD, of 1.5 microns displayed a maximum current density, IDSMAX, of 635 mA/mm with an applied gate voltage, VGS, of +2 V. Breakdown measurements on transistors with gate to drain spacing, LGD, of 770 nm had breakdown voltage greater than 220 , corresponding to minimum breakdown field of 2.86 MV/cm. This work provides a framework for the design of low resistance contacts to MOCVD grown high Al-content AlxGa1-xN channel transistors.