超薄势垒InAlN/GaN HFET器件高频特性分析

采用二次外延重掺杂n+ GaN实现非合金欧姆接触,并通过优化干法刻蚀和金属有机化学气相沉积(MOCVD)外延工艺,有效降低了欧姆接触电阻.将非合金欧姆接触工艺应用于InAlN/GaN异质结场效应晶体管(HFET)器件制备,器件的有效源漏间距缩小至600 nm.同时,结合40 nm T型栅工艺,制备了高电流截止频率(fT)和最大振荡频率(fmax)的InAlN/GaN HFET器件.结果显示减小欧姆接触电阻和栅长后,器件的电学特性,尤其是射频特性得到大幅提升.栅偏压为0V时,器件最大漏源饱和电流密度达到1.88 A/mm;直流峰值跨导达到681 mS/mm.根据射频小信号测试结果外推得到器件的fT和fmax同为217 GHz.

High-Frequency Characteristics Analysis of InAlN/GaN HFET Devices with Ultrathin Barrier Layer

Nonalloyed ohmic contacts were realized by regrown epitaxial heavily-doped n+ GaN.The ohmic contact resistance was reduced by improving the dry etching and metal organic chemical vapor deposition (MOCVD) epitaxial processes.Nonalloyed ohmic contacts process was used in the fabrication of InA1N/GaN heterostructure field-effect transistor (HFET) devices,in which the virtual source-to-drain distance was reduced to 600 nm.Meanwhile,with the 40 nm T-shaped gate process,InA1N/GaN HFET devices with high current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were fabricated.The results show that the electrical characteristics of the devices,especially for the RF characteristics,are improved greatly after the reduction of ohmic contact resistance and gate length.The maximum drain-source saturation current density reaches to 1.88 A/mm at the gate bias voltage of 0 V and the DC peak transconductance reaches to 681 mS/mm.The values offT andfmax were both extrapolated to be 217 GHz according to the RF small signal measurement results.