Growth Of Diamond By Using MPCVD System And Investigation Of Hydrogen Terminated Diamond Field Effect Transistors

Diamond is one of new generation ultra-wide bandgap semiconductor materials,and it has a series of excellent properties,such as,wide band gap,high carrier mobility,high breakdown voltage,high thermal conductivity,large hardness,and high chemical stability.Therefore,it is also called"the ultimate semiconductor".Diamond has great potential for applications in the area of high-frequency and high-power devices,optical windows,high-energy particle detectors,quantum information and biosensors.However,the lack of large area single crystal,high production cost,and the difficulty in doping obstruct the deveopment of diamond severely.Currently,most growth of single crystal diamond by using chemical vapor deposition?CVD?system is homoepitaxy on the single crytal diamond substrate grown by using high-pressure and high-temperature?HPHT?methods.However,the HPHT method is difficult to obtain large-size single crystals,which seriously limits the size of CVD grown single crystal diamonds.Thus,it is necessary to carry out the research on the expanding growth of single crystal diamond to obtain high-purity,high-quality and large-size single-crystal diamond.What's more,the activation energies of the most widely used boron and phosphorus dopants are 0.37 eV and 0.62 eV,respectively,which are so high that their ionization efficiency at room temperature is very low.Fortunately,after treating the diamond surface by using hydrogen plasma and exposing it to the air,a two-dimensional hole gas?2DHG?with the concentration of 10¹²¹0¹⁴ cm^-2can be formed on the surface.However,this 2DHG is unstable.Thus,the realization of high-performance,high-stability field-effect transistor devices based on the hydrogen-terminated diamonds still need constant efforts.Based on the above backgrounds,this dissertation focus on the growth of high-quality diamond materials and the research on high-performance diamond field effect transistors.It is expected that high-quality,large-area single-crystal diamond materials,as well as high-performance,high-stability diamond field-effect transistors can be realized.The main work and results of this dissertation are as follows.1.Based on MPCVD system,the processes of epitaxial growth of single crystal diamond were optimized,and the effects of methane concentration and argon addition on epitaxial growth of single crystal diamond were studied.The maximum growth rate reached more than 20?m/h without argon addition,and a growth rate of 43?m/h was achieved with a20%argon addition.The full width at half maximum?FWHM?of the XRD?004?rocking curve is measured to be 37.91 arcsec,which is comparable with the result of the electronic grade single crystal diamond?34.98 arcsec?from Element Six Ltd.In addition,our CVD grown single crystalline diamond has a nitrogen impurity concentration of 1 ppm or less,where the paramagnetic nitrogen impurity concentration is at the level of tens of ppb.2.A new expanding-growth technique of the of single crystal diamond was proposed.By stabilizing the heat exchange between the substrate and the substrate holder,keeping the constant values of growth processes parameters and the surface temperature of the substrate,and using a pocket substrate holder,the effectively enlarged growth of the single crystal diamond was realized.The single crystal diamond with a maximum edge length of10 mm was realized based on a substrate with a maximum edge length of 7.5 mm,which is the largest size of the literature reported results from China.We also innovatively achieved the simultaneous enlarged growth of multiple single-crystal diamond samples,and greatly improved the growth efficiency of single-crystal diamond under the premise of ensuring the uniformity of the material quality.3.The hydrogen termination diamond MESFETs were achieved based on CVD grown single crystal diamond.The on/off ratio of the device is as high as 10⁹,which is the highest level ever reported in the world.It indicates the high purity and high insularity of the CVD grown single crystal diamond.The device has an output current of 96 mA/mm and a subthreshold swing of 80 mV/dec.4.We fabricated the hydrogen terminated single crystalline diamond MOSFET with a MoO₃ gate dielectric for the first time.The transistors with 4-?m gate show a transconductance of 29 mS/mm and a saturation current of 33 mA/mm at V_GS=-1.5 V,respectively.The effective mobility is extracted to be 108 cm²/?Vs?from the relationship between the on resistance and|V_GS-V_TH|,and the carrier mobility is always a constant with the gate voltage shifting to the negative voltage from V_TH.In addition,the interface characteristics between the gate metal and MoO₃ were investigated and it was found that an unintentionally introduced alumina exists at the interface.5.The channel carrier transport characteristics of the single crystalline diamond MOSFET with MoO₃ gate dielectrics were studied based on the fat-gate devices.The calculated results indicate that the concentrations of fixed charge and trap in the oxide layer are1.67×10¹² cm^-2 and 1.35×10¹¹ cm^-2,respectively.The effective hole mobility reaches 210cm²/Vs.We also used the empirical formula of the relation between the carrier mobility and vertical electric field in the silicon MOS channel to fit the relationship between the carrier mobility and the gate voltage of the diamond device for the first time.The mobility degradation induced by vertical surface electric field was shown by the upper limit of the low-field mobility?₀=699 cm²/?V·s?and the mobility degradation factor?=1.13.6.The MOSFETs with MoO₃ gate dielectric were fabricated on polycrystalline diamond substrates.The device with a gate length of 2?m shows f_T=1.2 GHz and f_max=1.9 GHz.For the devices with MoO₃ passivation,the stability of the repeated I_DS^V_GS measurements was demonstrated by a mere I_Dsat decrease of 3.3%between the first and third sweepings.In addition,the devices worked well at 200°C and showed even larger I_Dsat than that at room temperature.7.The hydrogen-terminated polycrystalline diamond MOSFETs with Al₂O₃ passivation layer grown by atomic layer deposition at 200 ^oC and 300 ^oC were achieved by using gold mask technology,and the characteristics of devices were studied.The 2-?m gate length devices with 200°C grown Al₂O₃ dielectric achieve a maximum saturation drain current of339mA/mm,which is the maximum value for the diamond MOSFETs with the same gate length except the NO₂-adsorbed case.However,Al₂O₃ grown at 300°C has higher quality and the device can support higher gate voltage.In addition,both devices exhibited high stability after continuous test due to the effective protection of the hydrogen-terminated diamond surface after passivating the surface using Al₂O₃ dielectric.We expect to improve the performance of the device by reduce the thickness of the oxide layer grown at 200°C and stack another high-quality high k dielectric on it in the future studies.