| As one of the representatives of ultra wide band gap semiconductor materials,diamond has broad application prospects in high-frequency and high-power electronic devices.However,it is difficult to be doped.At present,diamond-based electronic devices are mainly fabricated on hydrogen-terminated diamond(H-dimaond)with a two-dimensional hole gas(2DHG)to realize electrical conductance.The 2DHG property is closely related to the property of the H-dimaond surface.Since the characteristics of the H-diamond surface with different orientations are different,it is necessary to study the single crystal diamond with different surface orientations in order to break through higher performance of diamond-based electronic devices.In addition,the 2DHG concentration on the hydrogenated-diamond can be more than 1013cm-2.Therefore,the H-dimaond MOSFET needs a gate insulator with high dielectric constant to control the large charge response under the external bias voltage.Then,the research on the high-k insulator/H-diamond structure is necessary.Based on the above research background,the research work and conclusions are as follows:The(100),(110)and(111)single-crystal diamond plates were got from the same single-crystal diamond sample by laser cutting and polishing.The AFM results show that after hydrogen plasma treatment,there are dense triangular pyramid-like etch pits and hawkeye-like etch pits with different sizes on the surfaces of(100)and(110)samples,respectively,and the surface roughness increases.The analysis shows that the etch pits are obtained by hydrogen plasma etching of dislocations extending to the surface of the original samples.The PL and Raman results show that the optical properties of(100),(110)and(111)diamond are similar.The Hall effect test shows that the sheet resistances of(110)and(111)samples are approximately equal,and significantly lower than that of(100)samples.In addition,the carrier concentration of(111)sample is the highest.The Al-gate MESFET with a gate length of 6?m were fabricated on(100)(device A),(110)(device B)and(111)(device C)single crystal diamonds,respectively.At VGS=-4 V,the on resistance of device C is 48.51?·mm,which is only 67%of device A and B,and the maximum saturation current is-80.41 mA/mm and approximately 1.4 times of device A and B.The maximum transconductance of the three samples is approximately equal,and they all have a large switch ratio of?108.The maximum carrier concentration of device C is 1.45×1013cm-2,which is approximately 1.1 times of device A and B.The main reason for the high saturation current and low on resistance of device C is that the carrier concentration is a little higher and the sheet resistance is lower.The interfacial band configuration between polycrystalline H-diamond and HfO2film was analyzed by XPS.The band gap of HfO2was calculated to be 5.16±0.2 eV,and the valence band offset(?EV)of HfO2/H-diamond interface was calculated to be 1.98±0.2 eV and the conduction band offset(?EC)is 2.29±0.2 eV.Then the complete HfO2/H-diamond interfacial band configuration was obtained.A 300?ALD grown HfO2film was used as gate dielectric as well as passivation layer.Two kinds of devices with or without gate-source distance were fabricated on the polycrystalline H-diamond substrate.The source-drain distance of the two devices was 6?m,and the gate length was 2?m(device A)and 6?m(device B),respectively.At VGS=-8 V,the saturated current of device A is 190.6 mA/mm,which is higher than 141.4 mA/mm of device B,but the on resistance of device B is 61.61?·mm,approximately half of that of device A.The carrier mobility of device B is 37.1 cm2/V·s,and it is almost unchanged in the largeVGSrange of-2 V to-8 V.Device A achieves a breakdown voltage of more than200 V.In addition,the stability of device A under saturation-region constant voltage stress is also characterized.In the first 30 minutes,12%-16%degradation of drain current of device A occurs,but in the next 30 minutes,it tends to be stable,only 6%degradation occurs. |
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