Study on H plasma treatment enhanced p-GaN gate AlGaN/GaN HEMT with block layer

High electron mobility transistors(HEMTs)show tremendous potentials for high mobility, high breakdownvoltage, low conduction, low power consumption, and occupy an important piece of the microelectronics field.The high-resistivity-cap-layer high electron mobility transistor (HRCL-HEMT) is a novel device structure.Based on the hole compensation mechanism, the p-GaN is converted into high resistance semiconductor materialby hydrogen plasma implantation. Thus, the surface of the p-GaN layer will have a serious bombardmentdamage under the hydrogen plasma implantation. In practical work, it is also very challenging in the accuratecontrolling of the hydrogen injection rate, injection depth and injection uniformity. To achieve the requireddepth of injection, the injected hydrogen plasma is often more than the required dose or multiple injectionstimes. The energy of hydrogen plasma plays a huge influence on the surface of the p-GaN layer.The leakagecurrent will be generated on the device surface, which deteriorates the electrical performance of the device. In this work, to protect the surface of p-GaN layer, a 2-nm Al2O3 film is deposited on the surface of the p-GaN cap layer to reduce the implantation damage caused by hydrogen plasma treatment. The research showsthat after the device deposited Al2O3 film prior to the hydrogen plasma treatment, the gate reverse leakagecurrent is reduced by an order of magnitude, the ratio of ION to IOFF is increased by about 3 times. Meanwhile,the OFF-state breakdown voltage is increased from 410 V to 780 V. In addition, when the bias voltage is 400 V,the values of dynamic RON of devices A and B are 1.49 and 1.45 respectively, the device B shows a more stabledynamic performance. To analyze the gate leakage mechanism, a temperature-dependent current IG-VG testingis carried out, and it is found that the dominant mechanism of gate leakage current is two-dimensional variablerange hopping (2D-VRH) at reverse gate voltage. The reason for reducing the gate reverse current is analyzed,and the Al2O3 film increases the activation energy of trap level and changes the surface states of HR-GaN;furthermore, the Al2O3 film blocks the injection of too much H plasma, thereby reducing the density of AlGaNbarrier and channel trap states, and weakening the current collapse.