Heterostructure and Interfacial Engineering for Low-Resistance Contacts to Ultra-Wide Bandgap AlGaN

TL;DR

This paper demonstrates a novel heterostructure engineering approach to achieve ultra-low contact resistivity in AlGaN devices through reverse grading and interfacial optimization, significantly outperforming previous methods.

Contribution

It introduces a reverse-graded contact layer with interfacial engineering that drastically reduces contact resistivity in ultra-wide bandgap AlGaN transistors.

Findings

Record low contact resistivity of 1.4 x 10^-6 Ohm.cm^2 achieved.

Reverse grading and interfacial engineering are key to reducing contact resistance.

Interfacial resistance due to bandgap narrowing dominates overall contact resistance.

Abstract

We report on the heterostructure and interfacial engineering of metalorganic chemical vapor deposition (MOCVD) grown reverse-graded contacts to ultra-wide bandgap AlGaN. A record low contact resistivity of 1.4 x 10-6 Ohm.cm2 was reported on an Al0.82Ga0.18N metal semiconductor field effect transistor (MESFET) by compositionally grading the contact layer from Al0.85Ga0.15N to Al0.14Ga0.86N with degenerate doping and proper interfacial engineering considering bandgap-narrowing-induced band offset between channel and contact layer. This represents orders-of-magnitude of lower contact resistivity than that obtained in similar MOCVD-grown structures. A detailed, layer-by-layer analysis of the reverse graded contact and TCAD simulation of the bandgap narrowing effect highlighted that the reverse graded contact layer itself is extremely conductive and interfacial resistance due to bandgap-narrowing-induced barrier between contact and channel dominates the contact resistance.