"Current Status and Future Prospects of GaN-based HEMTs"

Junya Yaita, Researcher, Fujitsu Laboratory, Japan

December 9th (Monday), 4:00pm
Engineering Science Bldg (ESB), Rm 2001
NOTE: Time Change

Gallium nitride based high electron mobility transistors (GaN HEMTs) have been demonstrated as high frequency and high power amplifiers, which is expected for wireless communications, radars and so on. It, basically, has AlGaN/GaN structures so far. In 2000s, InAlGaN and AlN layer on GaN channel layer have been reported. These devices, however, are useally operated at very high frequency with low breakdown voltage due to high 2DEG densities. In this study, we introduce high output power density InAlGaN/GaN HEMTs and thermal management technologies for GaN HEMTs.

Recently, we developed 4 technologies for improving GaN-based HEMTs performances; (i) Crystal growth technique towards increasing the 2DEG electron mobility of InAlGaN/GaN HEMTs. InAlGaN/GaN HEMTs with AlGaN spacer layer improve electron mobility without decreasing 2DEG density. (ii) Optimizing device structure applying n+-GaN regrowth and InGaN back-barrier layer. The regrowth layer and InGaN back barrier layer improve contact resistance and off-state leakage current, respectively. (iii) Thermal management using high thermal conductivity material of diamond for thermal dispassion of GaN HEMTs. Low thermal conductivity of GaN is one of the reason for limitations of GaN-HEMTs performance. We applied diamond towards GaN HEMTs by wafer bonding and direct growth techniques. (iv) Solving the trade-off relationships between breakdown voltage and high current density using asymmetric 2DEG densities. The different strain fields in AlO and MgO passivation layer enable to control 2DEG density in GaN channel. Using this phenomenon, we realize different 2DEG densities in the same plane of GaN HEMTs. This different 2DEG densities realize large drain current with high breakdown voltage, which is similar to conventional vertical transistors.

InAlGaN/GaN HEMTs we achieved high power density of 4.5 W/mm using crystal growth technique and optimizing device structure. Moreover, we applied diamond heat spreaders to the GaN HEMTs. The power density is up to 19.9 W/mm. The high power and high frequency amplifier of GaN HEMTs using these technologies accelerates the wireless communication technology.

About Junya Yaita:

• B. E. degree in electronic engineering from Kanazawa University, Japan in 2013
• M. E. and Ph. D degrees in electronic engineering from the Tokyo Institute of Technology, Tokyo, Japan, in 2015 and 2018.

Areas of Expertise and Interest: for my PhD thesis, I investigated heteroepitaxial growth of diamond films for power and sensor devices. Now, I work in Fujitsu laboratory and investigate GaN-based transistors for laser for high-frequency power amplifier. The diamond and GaN applications have been expected for next-generation RF-systems such as satellite communications. Therefore, I am interested in what kind of device performance are required for mm-wave systems.

• “Characterization of Schottky Barrier Diaodes on Heteroepitaxial Diamond on 3C-SiC/Si Substrates” IEEE TED submitted.
• "In-situ bias current monitoring of nucleation for epitaxial diamonds on 3C-SiC/Si substrates" Diamond & Related Materials, Vol. 88, pp. 158-162, (2018).
• “Preferentially-aligned nitrogen-vacancy centers in heteroepitaxial (111) diamonds on Si substrates via 3C-SiC intermediate layers" Appl. Phys. Express.11 045501 (2018).
• "Influence of High-Power-Density Plasma on Heteroepitaxial Diamond Nucleation on 3C-SiC Surface" Appl. Phys. Express. 10, 045502, (2017).
• "Highly oriented diamond (111) films synthesized by pulse bias-enhanced nucleation and epitaxial grain selection on a 3C-SiC/Si (111) substrate" Appl. Phys. Lett., 110, 062102, 2017.
• "Heteroepitaxial Growth of Diamond Films on 3C-SiC/Si Substrates with Utilization of Antenna- Edge Microwave Plasma CVD for Nucleation", Jananese Journal of Applied Physics, 54.4S 04DH13 (2015).
• "600 V Diamond Junction Field-Effect Transistors Operated at 200 °C", IEEE Electron Device Letters, 35.2, 241-243 (2013).
• "Improvement of fluorescence intensity of nitrogen vacancy centers in self-formed diamond microstructures", Applied Physics Letters, 107.16, 163012 (2015).

Hosted by: Prof. Mark Rodwell, ECE