Synthesis Of Nickel Nitride And Application In GaN-based Electronic Devices

With the development of information technology,wireless power transmission is attracting attention as one of the power supply technologies due to its crucial role.Schottky barrier diode(SBD)is a critical device of antenna-rectifier(rectenna)circuit in the microwave wireless power transmission systems,which is widely used in electric vehicle power charging,energy harvesting systems,power source,and in-building wireless power distribution.Gallium nitride(GaN)-based materials exhibit many extraordinary features,including large bandgap,higher breakdown field,higher electron mobility and higher electron saturation velocity,accordingly GaN SBDs have attracted much attention for improving the efficiency of microwave wireless power transmission system.However,the most common nickel(Ni)anode is reported to form a Ni-N alloy(a mixture of Ni3N,Ni4N,NiN and so on)after thermal treatment,resulting in the degradation of stability.This is required more stability materials to replace the Ni for the Schottky contact applicaion.However,the serious heat dissipation during static conduction and on/off switching cycles causes a high junction temperature.This will strongly deteriorate the safe and reliable operations.Therefore,the junction temperature measurement of power device plays a critical role in many applications.Many studies have demonstrated the possibility of junction temperature monitoring using a thermally stable SBD and/or pn diode(PND).Generally,the forward voltage of diode presents an excellent linear dependence on temperature when they are biased at a relatively small constant current.The sensing ability of a diode temperature sensor bases on the quasi-linear dependence of forward voltage on temperature,requiring good thermal stability and linearity.GaN-based electronic devices have shown the excellent thermal stability and strong temperature dependence,meaning that it can be a possible candidate for temperature sensing.In this thesis,we discussed the synthesis and application of nickel nitride for GaN electron devices application.Meanwhile,we also investigated the GaN based PND and SBD diodes for temperature sensor application.The main research contents and innovative research results can be summarized as follows:1.Nickel nitride(NixN)films were deposited by magnetron reactive sputtering under varying N2 partial pressure(P(N2))conditions range from 0.005 to 0.184 Pa.With the increasing of P(N2),the deposition rate decreases while the resistivity and root mean square roughness increase.X-ray diffraction(XRD)and X-ray photoelectron spectra(XPS)indicate that Ni4N and Ni3N phases dominate the films at]ow and medium P(N2),respectively.In addition,Ni2N phase can be also obtained at high P(N2).The Ni/N ratio evaluated from the XPS spectra is consistent with the NixN phases showed in the XRD spectra of different P(N2).2.NixN films prepared by magnetron reactive sputtering at different pressure ratios of Ar and N2 mixture gases,were employed as anode material for GaN SBD application.Comparing with the GaN diodes with Ni anode,the Schottky barrier height and turn-on voltage of the Schottky barrier diodes with NixN anode are increased with 0.03?0.18 eV and 0.03?0.15 V,respectively.Capacitance-voltage curves demonstrated that good interface quality with no obvious hysteresis is realized.Especially,Ni3N anode diodes obtaine at medium P(N2)possess a high barrier height and a low reverse leakage current and are regarded as a promising anode material.The temperature-dependent current-voltage characteristics demonstrate that the Ni3N-SBDs have better thermal stability than that of Ni-SBDs,owing to the suppression of interface reaction between Ni and GaN.In addition,the thermal stability of GaN diode with Ni3N anode is potential for temperature sensing application with the sensitivity of approximately 1.3 mV/K.3.NiO/GaN PNDs and TiN/GaN SBDs were investigated extensively by varying the device diameter and current level.For the NiO/GaN PND,the series resistance and ideality factor dominate the sensitivity at the fully-turn-on state.However,the series resistance weakly influenced the sensitivity of the TiN/GaN SBDs temperature sensor at the fully-turn-on state.After subtracting the component of series resistance,the sensitivity decreases and increases with the increased device diameters for the NiO/GaN PNDs and TiN/GaN SBDs temperature sensors,respectively.For both temperature sensors,in the sub-threshold state,a good linear relationship between sensitivity and the corresponding current density have been observed for devices with different diameters.A low current density is corresponding to the high sensitivity.The NiO/GaN PNDs and TiN/GaN SBDs presenting good thermal stability and linearity from 25 to 200? are promising candidates for temperature sensing application.5.We also investigated the NiN/GaN SBD for temperature sensor application.While in the sub-threshold region,a good linear relationship between sensitivity and the corresponding current density hav been observed for a 200 ?m diameter NiN/GaN SBD temperature sensor.By comparing whih TiN,Ni and NiN electrode GaN SBDs temperature sensors,the NiN electrode device shows a near-ideal theoretical sensitivity of the GaN SBD temperature sensor which is calculated by the thermionic emission model from GaN based SBDs.6.We also fabricated NiN-gated AlGaN/GaN Hetero-junction Field Effect Transistors(HFETs)by magnetron reactive sputtering with a Ni target in an ambient Ar and N2 mixture gas.Gete leakage current characteristics shows that the reverse leakage current of NiN-gated HFETs is approximately reduced by one order of magnitude and the ON/OFF drain current ratio increases two order of magnitudes comparing with the conventional Ni-gated HFETs.