| As a typical representative of the emerging ultra-wide band-gap semiconductor,gallium oxide has excellent properties such as extremely high breakdown field strength of 8MV/cm and ultra-wide band-gap width（4.8～4.9 e V）.Its Baliga quality factor is 3200,which is 10 times and 4 times of the wide band-gap semiconductor SiC and Ga N,respectively.At the same time,gallium oxide has the important advantage of large size and high quality single crystal substrate,which is easy to be prepared at low cost.Therefore,gallium oxide has become one of the ideal technology choices for ultra-high voltage,ultra-high energy efficiency and cost-effective next-generation power electronic devices,and has great application prospects in high-energy power grids,new energy vehicles,high-speed railways and other fields.Therefore,gallium oxide semiconductor has become the most popular new field of semiconductor research in recent years,and it has also become an important battlefield for the competition of major countries in the field of cutting-edge semiconductor technology.Although gallium oxide semiconductor material in the preparation of power electronic devices has a great potential,but to get to the ultra-high pressure gallium oxide power electronic devices,components of anodic electric field on the edge of the focus is to improve the pressure big challenges,need to conduct the thorough research to the new high voltage terminal structure,through the terminal of the structure of the innovation and the key technology and development,Continuously improve the performance of gallium oxide power electronic devices.At the same time,the p-type doping of Ga N semiconductor is difficult,which brings great challenges to the preparation of PN junction terminal and PN junction diode in power electronic devices.In this context,with the goal of improving the breakdown voltage and power optimal value of Ga N power diode,this paper proposes a variety of new terminal structures through in-depth research on material characteristics,device structure and device conductivity mechanism,and introduces p-type NiOxstructure.The significant hole superinjection effect in p-NiOx/n-Ga2O3heterojunction is confirmed and revealed for the first time.On this basis,a variety of new terminal Ga2O3Schottky diodes and Ga2O3heterojunction diodes with hole superinjection have been developed.The highest breakdown voltage of the device is over 8000 V.The highest power optimum is over 25.7 GW/cm2,which for the first time exceeds the physical limit of Ga N monopole devices.The research results have cleared a number of key technical obstacles for the rapid development and practical application of gallium oxide power diodes,and highlight the broad application prospects of gallium oxide in power electronic devices.The main research contents and achievements of this paper are as follows:1.The surface treatment technology and field plate structure of Ga2O3vertical Schottky diode are studied.Through process and structure optimization,the interface trap of passivation layer is reduced,the electric field distribution at the anode edge is improved,and the breakdown voltage of the device is significantly increased.Piranha solution was used to pretreat the surface of gallium oxide material,combined with hot oxygen annealing treatment,which significantly reduced the oxygen vacancies and hanging bonds on the surface of the material,and reduced the trapping density Qit at the Al2O3/Ga2O3interface from 8.8×1011cm-2to 6.5×1011cm-2.Through the internal electric field analysis of the device,the vertical Ga2O3Schottky diode with inclined field plate structure was optimized and designed.Based on the isotropic etching effect of F ion in BOE solution on SiO2passivation layer,the tilted anode groove was prepared in SiO2passivation layer,and the tilted field plate structure diode was realized.At the same length of the field plate,the voltage of the device is increased from 1850 V of the vertical field plate to 2200 V of the inclined field plate.2.Through structural simulation and process optimization,the Ga2O3Schottky diode with high voltage and high power optimal value of SiO2medium terminal structure is developed.The highest voltage and power optimal value are up to 6000 V and 10.6 GW/cm2,respectively.Firstly,the theoretical simulation of Ga2O3Schottky diodes with three kinds of SiO2thickness（300 nm,600 nm,1200 nm）is carried out.The electric field distribution under the device reverse bias and the influence of SiO2thickness and field plate length on the electric field distribution are analyzed,and the corresponding device structure is optimized and designed.Then three kinds of Ga2O3Schottky diodes with SiO2medium thickness of 300 nm,600 nm and 1200 nm were developed through self-alignment process and anodic thermal annealing interface repair process,and the breakdown voltages of the devices were 3.4 KV,4.3 KV and 6.0 KV,respectively.The on-resistance ranges from 3.3to 3.4 mΩ·cm2,and the optimal power values(P-FOM=BV2/Ron,sp)are 3.4,5.4 and 10.6GW/cm2,respectively.For the device with SiO2medium thickness of 1200 nm,the power optimal value is in the range of 7.4 to 10.6 GW/cm2,reaching the highest level reported internationally.3.Aiming at the problem of high carrier concentration in n-type gallium oxide epitaxial layer,the method that N and P ion implantation process and hot oxygen annealing process can effectively reduce the carrier concentration in the epitaxial layer is proposed and verified.The effective regulation of carrier concentration in the epitaxial layer is realized,and the exit plate structure p-NiOx/n-Ga2O3heterojunction diode is prepared.Compared with the device without epitaxial layer treatment,the voltage resistance of the device treated with N and P ion implantation process increased from 3.3 KV to 3.5 KV,and the on-resistance increased from 1.9 mΩ·cm2to 4 mΩ·cm2.The carrier concentration in the injection region of 500 nm epitaxial layer decreased from 3.2×1016cm-3to 7.2×1011cm-3.The device voltage resistance increased from 3.3 KV to 3.7 KV,the on-resistance increased from 1.9 mΩ·cm2to 3.3 mΩ·cm2,and the average carrier concentration in epitaxial layer decreased from 3.2×1016cm-3to 1×1016cm-3.4.A p-NiOx/n-Ga2O3heterojunction diode with a double-layer dielectric composite terminal structure with ultra-high voltage is proposed and developed.Firstly,the Ga2O3epitaxial material was treated by hot oxygen annealing at 500℃for 3 hours to reduce the carrier concentration in the epitaxial layer from 2×1016cm-3to 5-7×1015cm-3.Then,Mg ion was injected into the edge terminal and field plate structure to suppress the peak electric field intensity at the anode edge.Based on the thinning of Ga2O3substrate to improve the heat dissipation ability of the device,the high performance gallium oxide heterojunction diode（HJ-PND）with the highest breakdown voltage of 8.32 KV,conduction resistance of 5.24 mΩ·cm2,and power optimal value of 13.21 GW/cm2is finally realized.The average breakdown electric field strength of the device is up to 6.2MV/cm.5.Based on Mg ion implantation edge terminal,p-NiOxdielectric and Ga2O3epitaxial layer etching double isolation process and field plate structure,p-NiOx/n-Ga2O3heterojunction diode with power superior value beyond the single-pole limit of Gallium oxide was developed,and the significant hole superinjection effect in Gallium oxide heterojunction was confirmed for the first time.The hole lifetime in Gallium oxide is5.4-23.1 ns.Through the combination of simulation and experiment,the conductivity modulation effect of p-NiOx/n-Ga2O3heterojunction diode is deeply studied.It is found that there will be a significant hole overinjection phenomenon under the positive bias,which leads to a significant reduction in the on-resistance of the device.The minimum Ron,spis only 0.35 mΩ·cm2,and the breakdown voltage is more than 3 KV.The optimal P-FOM of the device power is up to 25.7 GW/cm2. |
