Physics of electrical degradation in GaN high electron mobility transistors

The deployment of GaN high electron mobility transistors (HEMT) in RF power applications is currently bottlenecked by their limited reliability. Obtaining the required reliability is a difficult issue due to the high voltage of operation. In order to improve reliability, it is essential to develop detailed physical understanding of the fundamental degradation mechanisms. In this thesis, we investigate the physical mechanisms behind the electrical degradation of GaN HEMTs by performing systematic stress experiments on devices provided by our industrial collaborators. These devices are electrically stressed under various bias conditions while regularly characterized by a benign characterization suite. We observe that electrical stress beyond a critical voltage results in an increase in drain resistance, a decrease in maximum drain current, and a sharp increase in reverse gate current. We show that this mode of degradation is driven by electric field and that current is less relevant. Behind this degradation is trap formation that occurs at the critical voltage. To understand this, we have developed a new trap-analysis methodology. It is found that under stress, the density of traps increases in the AlGaN barrier layer in the proximity to the gate edge on the drain side of the device. We show that this degradation is enhanced under mechanical uniaxial tensile strain that is externally applied to the device. From our experiments, we propose a degradation mechanism of defect formation through the inverse piezoelectric. In this mechanism, high vertical electric field at the gate edge under high voltage increases tensile stress in the AlGaN layer due to piezoelectricity of the material.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Joh, Jungwoo

Advisor dc:contributor.advisor

• Jesús A. del Alamo.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/55116

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/55116