SUBJECT: Ph.D. Proposal Presentation
BY: Georges Pavlidis
TIME: Wednesday, May 3, 2017, 3:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Assessing the Performance and Reliability of Gallium Nitride Based Electronics via Optical and Electrical Methods
COMMITTEE: Dr. Samuel Graham, Chair (ME)
Dr. Eric R. Heller (AFRL)
Dr. Peter J. Hesketh (ME)
Dr. Satish Kumar (ME)
Dr. John D. Cressler (ECE)
Dr. Shyh-Chiang Shen (ECE)


Gallium nitride (GaN) based electronics have shown great potential for RF devices and power electronics. Its superior material properties have enabled the fabrication of high frequency and high voltage devices. To minimize the device cost and avoid the challenges of fabricating bulk material, GaN is heteroepitaxially grown on substrates such as Si and SiC. The growth of GaN on foreign substrates leads to the formation of defects which can affect the device's electrical and thermal performance. The quantification of performance parameters such as the gate junction temperature and hot electron trapping is thus necessary to accurately assess the device's quality and lifetime. Until now, under DC conditions, Raman thermometry has shown to be the most accurate method to estimate the junction temperature. This method, however, requires a complex setup and long acquisition periods. To address the need for a fast and accurate technique, an electrical method is proposed using the change in resistance of the gate metal. The accuracy of this technique is verified via Raman thermometry. Overall, these techniques enable a deeper understanding of the device's degradation mechanisms under DC biasing. Devices, however, are normally operated under pulsed biasing conditions and the need of transient characterization is necessary. A new transient thermoreflectance imaging technique is used along with measuring transiently the gate resistance to estimate the device's temperature rise. Overall, the methods proposed in this study are shown to have great accuracy when assessing the electrical and thermal performance of GaN electronics.