High breakdown voltage lateral AlGaN/GaN high electron mobility transistor with p-GaN islands buried buffer layer for power applications
Authors: Zhang Li  , Lin Zhi-Yu  , Luo Jun  , Wang Shu-Long  , Zhang Jin-Cheng  , Hao Yue  , Dai Yang  , Chen Da-Zheng  , Guo Li-Xin  ,   Key Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi'an 710000, China;,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710000, China
Published: December 2020

The relatively low breakdown voltage (BV) seriously restricts the high power application of GaN based high electron mobility transistors (HEMTs). In this work, a novel AlGaN/GaN HEMT with buried p-n junctions is investigated to improve the breakdown characteristics by introducing six equidistant p-GaN islands buried buffer layer (PIBL) into the n-GaN epitaxial layer. The p-GaN islands act as reversed p-n junctions, which produces new electric field peaks at the edges of p-GaN islands, then realizing a much high breakdown voltage, and the reversed p-n junctions can help to suppress punch-through effect in buffer layer. Furthermore, the characteristics of proposed device are analyzed in detail from the aspects of off-state I-V characteristics, equipotential contour distribution, off-state electric field distribution, offstate carrier distribution and output characteristics. Simulated equipotential contour distribution shows that under the condition of high-voltage blocking state, multiple reverse p-n junctions introduced by the buried p-GaN islands produce five new electric field peaks, realizing a more uniform equipotential contour distribution especially at the edges of the buried p-islands. Then off-state electric field distribution demonstrates that p-GaN islands modulate the surface and bulk electric fields, which makes the voltage distributed in a larger area, therefore presenting a much higher breakdown voltage. It can be seen from off-state carrier distribution that the electrons in the buffer layer fully depleted in PIBL HEMT effectively suppress the buffer leakage current, thus alleviating the buffer-leakage-induced impact ionization leading to a high breakdown BV of over 1700 V with gate-to-drain length of 10μm, which is nearly 3 times larger than BV of 580 V in conventional AlGaN/GaN HEMT. Although, the introduction of p-type buried layer narrows the current path and causes an improved on-resistance, simulation shows that the specific on-resistance (Ron,sp) of PIBL HEMT is only about 1.47 mΩ·cm2, while the BV of the PIBL device is over 1700 V, and the obtained figure of merit (FOM=BV2/Ron,sp) reaches as high as 1966 MW·cm-2. The optimization of device structure reveals that when the distance between p-GaN layer and AlGaN layer (t) is 0.2μm, a thinner buried p-GaN island (tp) should help to realize a more significant electric field modulation, and PIBL HEMT can achieve a maximum BV of 1789 V with a tp=0.1μm. Compared with the traditional AlGaN/GaN HEMT, the PIBL HEMT reveals a higher breakdown voltage, meanwhile ensuring low Ron,sp, which makes this structure a promising candidate in the applications of high power electronic devices.