Dynamic Behavior Improvement of Normally-Off p-GaN High-Electron-Mobility Transistor Through a Low-Temperature Microwave Annealing Process

Hsien-Chin Chiu,Feng-Tso Chien,Yi-Sheng Chang,Chia-Hao Liu,Hsuan-Ling Kao,Chih-Wei Hu,Rong Xuan

doi:10.1109/jeds.2019.2941519

Hsien-Chin Chiu, Feng-Tso Chien + Show 5 more

Open Access

https://doi.org/10.1109/jeds.2019.2941519

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Abstract

The surface morphology optimization of ohmic contacts and the Mg out-diffusion suppression of normally off p-GaN gate high-electron-mobility transistors (HEMTs) continue to be challenges in the power electronics industry in terms of the high-frequency switching efficiency. In this study, better current density and reliable dynamic behaviors of p-GaN gate HEMTs were obtained simultaneously by adopting low-temperature microwave annealing (MWA) for the first time. Moreover, HEMTs fabricated using MWA have a higher ION/IOF ratio and lower gate leakage current than the HEMTs fabricated using rapid thermal annealing. Due to the local heating effect, a direct path for electron flow can be formed between the two-dimensional electron gas and the ohmic metals with low bulges surface. Moreover, the Mg out-diffusion of p-GaN gate layer was also suppressed to maintain good current density and low interface traps.

Highlights

GaN-based normally-off high-electron-mobility transistors (HEMTs) with a p-GaN gate structure was implemented to demonstrate single-chip solutions for high-efficiency and compact power conversion systems [1], [3]
The use of the low-temperature microwave annealing (MWA) technique resulted in comparatively superior electrical characteristics and a much smoother surface of the MWAHEMTs than those of RTA-HEMTs
The MWA-HEMT exhibited a leakage current of as low as 10−8 mA/mm, which was approximately two orders of magnitude lower than the current exhibited by the RTA-HEMT

Summary

INTRODUCTION

GaN-based normally-off HEMT with a p-GaN gate structure was implemented to demonstrate single-chip solutions for high-efficiency and compact power conversion systems [1], [3]. Based on previous studies, there are two major challenges that dominate the reliability and dynamic behavior of p-GaN gate HEMTs after the high-temperature annealing process. The out-diffusion of Mg into the p-GaN layers results in a low energy level (EC = −3.93 eV). We overcame these drawbacks of the traditional p-GaN gate HEMT by adopting a low-temperature microwave annealing (MWA) process together with a p-GaN/AlN/AlGaN/GaN hetero- structure design. The smooth ohmic metal contacts on an AlGaN/GaN heterostructure were obtained by conducting MWA in a low-temperature (450◦C–550◦C) ohmic contact formation environment. Mg out-diffusion into the p-GaN/AlN/Al0.17Ga0.83N/GaN heterostructure beneath the gate metal was suppressed

DEVICE STRUCTURE AND FABRICATION

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Findings

CONCLUSION