具有阻挡层的H等离子体处理增强型p-GaN栅AlGaN/GaN HEMT研究

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

采用H等离子体处理p-GaN盖帽层来制备p-GaN栅AlGaN/GaN高电子迁移率晶体管(HEMT).在p-GaN层表面上先沉积2 nm的Al_(2)O_(3)薄膜,以减少H等离子体注入p-GaN时对表面造成的损伤.经研究表明沉积Al_(2)O_(3)阻挡层的器件栅极反向泄漏电流降低了一个数量级,开关比提高了约3倍.由于栅极泄露电流的减小,关态击穿电压从410 V提高到780 V.针对栅极反向泄漏减小的现象,进行了变温I_(G)-V_(G)测试,验证了栅极反向泄漏电流的主导机制是二维变程跳跃(Two-dimensional variable range hopping,2D-VRH)模型.分析了减小栅极反向电流的原因是由于Al_(2)O_(3)阻挡层改变了HR-GaN的表面态,使陷阱能级的活化能升高.此外,器件动态特性也表现出更稳定的趋势,这是Al_(2)O_(3)薄膜阻挡过多的H等离子体的注入,使AlGaN势垒和沟道陷阱态数量减少,电流崩塌效应减弱.

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.In this work,to protect the surface of p-GaN layer,a 2-nm Al_(2)O_(3) 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 Al_(2)O_(3) film prior to the hydrogen plasma treatment,the gate reverse leakage current 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 stable dynamic performance.To analyze the gate leakage mechanism,a temperature-dependent current I_(G)-V_(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 Al_(2)O_(3) film increases the activation energy of trap level and changes the surface states of HR-GaN;furthermore,the Al_(2)O_(3) 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.