1.State Key Discipline Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071, China 2.Shaanxi Joint Key Laboratory of Graphene, Xi’an 710071, China
Fund Project:Project supported by the National Key Research and Development Program of China (Grant No. 2018YFB0406504), the Foundation of State Key Laboratory of China (Grant No. 6142605180102), the National Natural Science Foundation of China (Grant No. 61874080), and the National Postdoctoral Program for Innovative Talents (Grant No. BX20190263)
Received Date:02 July 2019
Accepted Date:05 November 2019
Published Online:20 January 2020
Abstract:Diamond has great potential applications in high-power, high-frequency semiconductor devices because of its wide band gap (5.5 eV), high thermal conductivity (22W/(cm·K)), and high carrier mobility (4500 cm2/(V·s) for electron, and 3800 cm2/(V·s) for hole). It has been widely considered as an ultimate semiconductor. From the analysis of our previous work, we find that the output current of field effect transistor based on hydrogen-terminated polycrystalline diamond is usually larger than that based on single crystal diamond, and that the preferential orientations of the polycrystalline diamond are mainly $ \langle 110\rangle $ and $ \langle 111\rangle $ shown by XRD results. Therefore, in order to further analyze the effect of surface orientation on the device performance of hydrogen-terminated diamond field effect transistor (FET), we study the devices fabricated respectively on the (110) plane and (111) plane single crystal diamond plates obtained from a single 3.5-mm-thick single crystal diamond grown by the microwave plasma chemical vapor deposition on the high-pressure high-temperature synthesized diamond substrate. Prior to processing the device, these diamond plates are characterized by atomic force microscope, Raman spectra and photoluminescence (PL) spectra. The results of Raman and PL spectra show that (110) plane and (111) plane plates originating from the same CVD single crystal diamond have no significant difference in optical property. Then the normally-on hydrogen-terminated diamond FET with a gate length of 6 μm is achieved. The device on (111) plane delivers a saturation drain current of 80.41 mA/mm at a gate voltage VGS = –4 V, which is approximately 1.4 times that of the device on (110) plane. Meanwhile, the on-resistance of the device on (111) plane is 48.51 Ω·mm, and it is only 67% of the device on (110) plane. Analyses of the capacitance-voltage show that the hole concentration of the gated device on (110) plane and (111) plane are 1.34 × 1013 cm–2 and 1.45 × 1013 cm–2, respectively, approximately at the same level. In addition, the hole density of the device on both (110) and (111) plane increase near-linearly with the increase of gate voltage from the threshold voltage to – 4 V, indicating that the control effect of the gate on the carrier in the channel is uniform. The possible reason for the higher saturation drain current as well as the lower on-resistance of the device on (111) plane is that its sheet resistance is lower. Keywords:single crystal diamond/ (110) plane/ (111) plane/ field effect transistors
图 7 转移特性 (a)器件A; (b)器件B Figure7. Transfer and transconductance characteristics: (a) Device A; (b) device B.
图8总结了部分已报道的栅长4—11 μm的单晶金刚石场效应管最大饱和电流和最大跨导值随栅长的变化关系, 同时列入本文的器件数据. 可以发现, 在长沟道器件中, 栅长6 μm的器件获得的最大饱和电流和跨导都拥有明显的优势, 尤其是(111)金刚石上的器件B. 图 8 氢终端金刚石场效应管输出电流(a)和最大跨导(b)随栅长的变化(数据来自文献[26,27,29—33]), MOSFET器件给出了栅金属和栅介质 Figure8. Summary of the reported (a) IDmax and (b) maximum transconductance of hydrogen-terminated diamond FETs dependent on the gate length[26,27,29-33]. The gate metal and gate dielectric are given for MOSFETs.
场效应管器件的特性主要由栅下沟道中载流子浓度、分布以及输运特性来决定的. 为了深入分析器件的特性, 测试了器件在1 MHz下栅-源二极管的C-V曲线, 结果如图9所示. 设栅下沟道中载流子的浓度为pch, 通过C-V曲线以及关系式$p_{\rm{ch}} = \dfrac{1}{e}\displaystyle\int {C_{\rm{GS}}{\rm{d}}V_{\rm{GS}}} $(e为基本电荷电量1.6 × 10–19 C), 可以计算得到器件A的沟道载流子最大浓度为1.34 × 1013 cm–2, 器件B的为1.45 × 1013 cm–2, 近似是器件A的1.08倍. 图 9 栅源二极管的C-V特性以及计算出的沟道载流子浓度随VGS的变化 (a)器件A; (b)器件B Figure9. Capacitance-voltage characteristics of the gate-source diode and the calculated hole density in the gated channel as a function of VGS: (a) Device A; (b) device B.