AlGaN/GaN双异质结F注入增强型高电子迁移率晶体管∗

摘要

理论模拟了不同GaN沟道厚度的双异质结(AlGaN/GaN/AlGaN/GaN)材料对高电子迁移率晶体管(HEMT)特性的影响，并模拟了不同F注入剂量下用该材料制作的增强型器件的特性差异。采用双异质结材料，结合F注入工艺成功地研制出了较高正向阈值电压的增强型HEMT器件。实验研究了三种GaN沟道厚度制作的增强型器件直流特性的差异，与模拟结果进行了对比验证。采用降低的F 注入等离子体功率，减小了等离子体处理工艺对器件沟道迁移率的损伤，研制出的器件未经高温退火即实现了较高的跨导和饱和电流特性。对14 nm GaN沟道厚度的器件进行了阈值电压温度稳定性和栅泄漏电流的比较研究，并且分析了双异质结器件的漏致势垒降低效应。%Effects of double heterostructure materials (AlGaN/GaN/AlGaN/GaN) with different GaN channel thickness values (14 nm, 28 nm, 60 nm) on the high electron mobility transistor (HEMT) are simulated by using silvaco, and furthermore, the differences in characteristic among the enhancement mode devices made from such double heterostructure materials with different F injection doses (150 W, 135 W) are also simulated. The simulation results show that the threshold voltage shifts towards positive direction and the saturation current decreases as the GaN channel thickness decreases. The two-dimensional electron gas (2 DEG) density could be reduced as GaN channel thickness decreases due to piezoelectric polarization weakened by backing AlGaN barrier. Combining F plasma treatment and double heterostructure material, the enhancement mode device with high positive threshold voltage is successfully developed. The DC characteristics of the enhancement mode devices with different GaN channel thickness values are analyzed comparatively, and the simulation results are validated by using the experimental results. The threshold voltages of these enhancement mode devices with GaN channel thickness values of 14 nm, 28 nm, and 60 nm reach 1.1 V, 0.8 V, and 0.3 V, respectively. The maximum transconductance values of these enhancement mode devices with GaN channel thickness values of 14 nm, 28 nm, and 60 nm reach 115 mS/mm, 137 mS/mm, and 198 mS/mm, respectively. The thinner GaN channel thickness in the double heterostructure could reduce the depth of quantum well and 2 DEG density, so that the device with a GaN channel thickness of 14 cm has a lower saturation current. The breakdown voltages and gate reverse leakage currents of the three kinds of devices are investigated, and the device with a thinner GaN channel has a lower leakage current and higher breakdown voltage due to weakened vertical electrical field in thinner channel double heterostructure. The damage of channel mobility in F plasma treatment is weakened by using a lower plasma power (135 W), and the enhancement mode device without annealing process demonstrates a better saturation current and transconductance characteristic. The results of the device with annealing confirm that the plasma damage is depressed at an F injection power of 135 W. The threshold voltage temperature stability of 14 nm GaN channel thickness device is studied, and∆Vth is only 0.4 V after 350 ◦C 2 min annealing process. Drain induced barrier lowering (DIBL) effects of the HEMTs with double heterostructures are investigated, and the DIBL value of the14 nm GaN channel device is 16 mV/V. The DIBL value indicates a good limiting property of the 2 DEG in double heterostructure device.