| Diamond has the characteristics of ultra-wide bandgap(5.5 eV),high thermal conductivity,high intrinsic mobility,high breakdown electric field,high saturation velocity,and low dielectric constant.It has great application potential in the fields of microwave power and power electronic devices.Hydrogen-and silicon-termination are two termination techniques that utilize hydrogen and silicon atoms to modify the diamond surface,respectively.Compared with other termination technologies,they have the characteristics of high carrier concentration and good insulator/diamond interface quality,respectively.Metal-oxide-semiconductor field-effect transistors(MOSFETs)made of hydrogen-and silicon-terminated diamond as device channels are currently a research hotspot in the field of diamond semiconductor devices.However,the current hydrogen-and silicon-terminated diamond MOSFET devices still suffer from unclear mechanisms,immature structures and processes,resulting in a large gap between the actual performance of the devices and the theoretical values,and there is an urgent need to carry out research on device mechanisms and models,device structures,and manufacturing processes.Therefore,this dissertation carries out research work targeting hydrogen-terminated diamond device modeling,high linearity hydrogenterminated diamond devices,high current and high threshold voltage silicon-terminated diamond devices,which are divided into four parts as follows.(1)In view of the problem that the existing empirical-based large-signal model of hydrogen-terminated diamond devices has excessive fitting parameters,it is difficult for the model to guide device optimization and circuit design,thus a quasi-physical-based nonlinear model with clear physical meaning and fewer fitting parameters is proposed.The proposed quasi-physical-based large-signal modeling method realizes the accurate modeling of the large-signal characteristics of hydrogen-terminated diamond devices.This method firstly establishes a numerical physical model that can accurately characterize the physical mechanism of surface adsorbates and carbon-hydrogen(C-H)dipole of hydrogen-terminated diamond to obtain the carrier concentration and electric field distribution,and then carries out the analytical modeling of drain current based on the zone division theory,and finally achieves the accuracy of saturation power over 90%.The drain current model contains only seven fitting parameters,which is more than 30%less than the conventional empirical model.(2)In view of the problem of poor linearity of conventional hydrogen terminated diamond devices due to the high fixed-charge content of low-temperature(atomic-layer-deposited Al2O3,ALD-Al2O3)gate dielectric prepared by oxygen plasma precursors,a low fixed-charge low-temperature ALD-Al2O3 gate dielectric process using water(H2O)precursor was proposed to develop hydrogen-terminated diamond devices,and accordingly a high-linearity hydrogen-terminated diamond device was achieved.This process breaks the key bottleneck of poor device mobility and linearity due to the high fixed-charge content of traditional ALD-Al2O3 gate dielectric,the results show that the prepared ALD-Al2O3 films have achieved a low fixed-charge content of 3.7 × 1012 cm-2 and a stable effective mobility of 105～200 cm2/V·s.The experimental results show that the proposed devices achieve a linearity figure-of-merit(gm_max×GVS)greater than 673 V·mS/mm,which is more than double that of the devices prepared by the low-temperature ALD-Al2O3 process using oxygen plasma precursors.(3)In view of the problems of low output current and poor threshold voltage(VTH)stability of the existed silicon-terminated diamond devices due to the low quality of gate dielectric,a gate dielectric reset process optimization method with the post-reset dielectric having better uniformity is proposed to break through the key bottleneck of device performance optimization due to the unclear reaction mechanism of silicon-termination formation by the selective growth method.As a result,an effective improvement of device output current and VTH stability is achieved at the same time.By removing the SiO2 mask with poor quality after selective growth of p++-Diamond,and then depositing an ALD-Al2O3 film,the reset of the gate dielectric of the silicon-terminated diamond device is realized.The experimental results show that this method achieves a maximum drain current density(|ID_max|)greater than 310 mA/mm,which is nearly double that of the conventional silicon-terminated diamond devices prepared by retaining the low quality SiO2 mask as the gate dielectric,and the VTH fluctuation range of the prepared devices with different channel lengths is 0.5 V,which is 93%lower than that of the conventional silicon-terminated diamond devices mentioned above..(4)In view of the problem of insufficient silicon(Si)density on the diamond surface for the preparation of silicon-terminated diamond devices by the selective growth method,a device realization method based on molecular beam deposition technology for the preparation of high-density silicon-terminated devices is proposed to realize the preparation of Si films with high density and controllable thickness,which can effectively increase the density of silicon-termination on diamond surface and facilitate the stable and controllable preparation of high VTH silicon-terminated diamond devices.Furthermore,a flat-band voltage(Vfb)extraction method is proposed by locating the center of the capacitance "dip" in the high-frequency capacitance-voltage(C-V)curve to obtain a positive fixed charge density of～7.8 × 1011 cm-2 for the Al2O3/oxidised high-density silicon-termination interface,revealing the operating principle of the enhancement-mode device.In addition,in order to break the key bottleneck of the lack of suitable ohmic contacts for the preparation of silicon-terminated diamond devices by using molecular Si beam deposition,we propose the device realization method of using metal mask to firstly prepare p++-Diamond(p++-Diamond-First)as the ohmic contact,and then using molecular beam deposited Si film as the channel.The experimental results show that |VTH| of the devices with different channel lengths prepared by this method is more than 10 V,which is nearly double that of similar MOS structure devices prepared by the selective growth method,and the VTH fluctuation range of the devices is only 0.2 V,which is 97%lower than that of the conventional silicon-terminated diamond devices. |
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