高跨导氢终端多晶金刚石长沟道场效应晶体管特性研究

Characterization of high-transconductance long-channel hydrogen-terminated polycrystal diamond field effect transistor

基于多晶金刚石制作了栅长为4 pm的铝栅氢终端金刚石场效应晶体管.器件的饱和漏源电流为160 mA/mm,导通电阻低达37.85Ω·mm,最大跨导达到32 mS/mm,且跨导高于最大值的90%的栅压(V_(GS))范围达到3 V(-2 V≤V_(GS)≤-5 V).通过传输线电阻分析以及器件的导通电阻和电容-电压特性分析,发现氢终端多晶金刚石栅下沟道中的空穴面浓度达到了1.56×10^(13)cm^(-2),有效迁移率在前述高跨导栅压范围保持在约170 cm^2/(V·s).分析认为,较低的栅源和栅漏串联电阻、沟道中高密度的载流子和在大范围栅压内的高水平迁移率是引起高而宽阔的跨导峰和低导通电阻的原因.

Diamond has a great potential to be used in high-power, high-voltage and high-frequency semiconductor devices due to its wide band gap （5.5 eV）, high breakdown field （〉 10 MV/cm）, high thermal conductivity （22 W/（cm.K））, and good carrier transport property. High-quality polycrystal diamond with large size wafers （up to several inches） is more easily obtained than the expensive monocrystal diamond plate with the size of only several mm2, and the good performance of electronic device on polycrystal diamond has been reported. So we fabricate a normally-on hydrogen-terminated polycrystal diamond field effect transistor with a 4-pm aluminum gate by using a gold mask process. The saturation drain current is 160 mA/mm, and the on-resistance is as low as 37.85 Ω.mm. The maximum transconductance reaches 32 mS/mm, and the gate voltage range with the transconductance higher than 90% of its maximum value reaches 3 V （-2 V·VGS≤-5 V）. An Ohmic contact resistance of 5.52 Ω.mm and a quite low square resistance of 5.71 kΩ/sq for the hydrogen-terminated diamond are extracted from the analysis of transmission line model measurement. On the basis of the analyses of the obtained results, the on-resistance of device dependent on gate voltage, and the capacitance-voltage data measured at the gate-source diode, we find that the hole sheet density under the gate reaches 1.56×10^13 cm^-2 at a gate voltage of -5 V, and the extracted effective mobility of the holes stays at about 170 cm^2/（V.S） in the aforementioned gate voltage range with high transcondnctance. In summary, the high and broad transconductance peak and the low on-resistance are attributed to the relatively low gate-source and gate-drain series resistance, the high-density carriers in the channel, and the high-level mobility achieved over a large gate voltage range. The relevant research of finding proper dielectrics for the gate insulator and the passivation layer is under way to further improve the device performance.