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

Abstract

<sec>High electron mobility transistors(HEMTs)show tremendous potentials for high mobility, high breakdown voltage, 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 material by hydrogen plasma implantation. Thus, the surface of the p-GaN layer will have a serious bombardment damage under the hydrogen plasma implantation. In practical work, it is also very challenging in the accurate controlling of the hydrogen injection rate, injection depth and injection uniformity. To achieve the required depth of injection, the injected hydrogen plasma is often more than the required dose or multiple injections times. The energy of hydrogen plasma plays a huge influence on the surface of the p-GaN layer.The leakage current will be generated on the device surface, which deteriorates the electrical performance of the device.</sec><sec>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 shows that after the device deposited Al₂O₃ film prior to the hydrogen plasma treatment, the gate reverse leakage current is reduced by an order of magnitude, the ratio of <i>I</i>_ON to <i>I</i>_OFF 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 <i>R</i>_ON of devices A and B are 1.49 and 1.45 respectively, the device B shows a more stable dynamic performance. To analyze the gate leakage mechanism, a temperature-dependent current<i> I</i>_G-<i>V</i>_G testing is carried out, and it is found that the dominant mechanism of gate leakage current is two-dimensional variable range 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 AlGaN barrier and channel trap states, and weakening the current collapse.</sec>