A Sub-Critical Barrier Thickness Normally-Off AlGaN/GaN MOS-HEMT

Raphael Brown,Xu Li Xu Li,Douglas Macfarlane,Edward Wasige,Gary Ternent,Abdullah Al-Khalidi,Iain Thayne,Haiping Zhou Haiping Zhou

doi:10.1109/led.2014.2334394

Raphael Brown, Xu Li Xu Li + Show 6 more

Open Access

https://doi.org/10.1109/led.2014.2334394

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Journal: IEEE Electron Device Letters	Publication Date: Sep 1, 2014
Citations: 52	License type: CC BY 3.0

Affiliation: University of Glasgow

Abstract

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al 0.25 Ga 0.75 N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO 2 ) as the gate dielectric. They demonstrated threshold voltages (V th ) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (V GS ) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices.

Highlights

G ALLIUM nitride (GaN) based wide bandgap semiconductor transistor technologies demonstrate high breakdown electric fields and high current densities, and so are actively being researched for power electronics applications
Conventional GaN-based HEMTs are of depletion mode type but enhancement mode (E-mode) or normally-off devices would be preferable for power electronics since they simplify circuit design and provide highly desirable essential feature of fail-safe operation [1], [2]
Common approaches to achieve normally-off GaN-based HEMTs are based on the conventional d-mode devices (∼20nm thick AlGaN barrier (∼25% Al-content) with an inherent two dimensional electron gas (2DEG) channel) and include recessed-gate, fluorine ion implantation or growth of a p-type GaN or AlGaN cap layer to locally deplete the channel underneath the gate [2]

Summary

INTRODUCTION

G ALLIUM nitride (GaN) based wide bandgap semiconductor transistor technologies demonstrate high breakdown electric fields and high current densities, and so are actively being researched for power electronics applications. Common approaches to achieve normally-off GaN-based HEMTs are based on the conventional d-mode devices (∼20nm thick AlGaN barrier (∼25% Al-content) with an inherent two dimensional electron gas (2DEG) channel) and include recessed-gate, fluorine ion implantation or growth of a p-type GaN or AlGaN cap layer to locally deplete the channel underneath the gate [2]. These approaches suffer from non-uniformity in device performance, device instability and Manuscript received May 31, 2014; accepted June 23, 2014. Normallyoff operation was attributed to negative charge in the gate dielectric which depleted the 2DEG channel for VGS < Vth. This letter describes a high performance E-mode AlGaN/GaN MOS-HEMT similar in layout to that in Refs. Devices with high positive threshold voltages and high current operation have been demonstrated

DEVICE STRUCTURE AND FABRICATION

DEVICE OUTPUT AND TRANSFER CHARACTERISTICS

OFF-STATE BREAKDOWN CHARACTERISTICS

CONCLUSION