多场环结构对GaN基JBS击穿电压和正向工作电流的影响

Effects of multi field ring edge termination on the breakdown voltage and forward current for GaN-based junction barrier Schottky diode

通过TCAD仿真模拟计算,系统地研究了不同结构参数对GaN基结势垒肖特基二极管(Junction Barrier Schottky Diode)电学特性的影响。JBS二极管在肖特基接触下方以若干个p型场环取代N--GaN漂移区,通过电荷耦合效应降低肖特基接触位置的电场强度,减弱镜像力的影响以达到减小反向漏电和提高击穿电压的效果。研究表明,P-GaN场环的厚度、掺杂浓度及场环的间隔均对器件的反向击穿电压有明显影响。例如,采用适当厚度的场环可以显著降低反偏状态下肖特基接触位置下方的电场强度,同时不会产生过大的pn结漏电,最优厚度300 nm的场环可以实现1 120 V的击穿电压。同时,由于阳极金属分别与N--GaN和P-GaN形成肖特基接触和欧姆接触,JBS二极管可以实现低开启电压。当pn开启后,P-GaN内空穴注入漂移区产生电导调制效应,有助于提高正向电流密度。

We systematically investigate the impact of different structural parameters on the electrical characteristic for GaN-based junction barrier schottky(JBS) diode with the help of TCAD simulation tools. The N--GaN drift region under the Schottky contact is partly replaced by several p-type GaN field rings, so the electric field magnitude at/near the Schottky contact interface can be markedly reduced by using the charge-coupling effect. The charge-coupling effect results in the weakened image force, and thus the decreased leakage current and increased breakdown voltage(BV) can be obtained. According to our results, the thickness, p-type doping concentration, and the spacing of the P-GaN field ring have a significant impact on the reverse blocking characteristics for the studied devices. In the reverse bias state, the electric field magnitude at the Schottky contact interface can be reduced by using a field ring with an optimized thickness, e.g., the BV can reach ~1 120 V when the field ring with the 300 nm thickness is used. At the same time, the leakage current at p-n junction will not be greatly increased. Meanwhile, the JBS diode can achieve a low turn-on voltage(VON) when the anode metal forms the Schottky contact and ohmic contact on the N--GaN and P-GaN, respectively.When the p-n junction is turned on, the hole injection into the drift region produces an enhanced conductance modulation effect, then the forward current density can be increased.