Research Of Breakdown Characteristics In Gallium Oxide Lateral Field-Effect Transistors

As an emerging wide-bandgap semiconductor material,Ga₂O₃（gallium oxide）has a bandgap width of 4.8 e V and a critical breakdown electric field of 8 MV/cm,all of which surpass the theoretical limits of Ga N and Si C materials.With the rapid development of large-size,low-cost Ga₂O₃ bulk single crystal preparation and high-quality epitaxial technology,the application of gallium oxide in power devices has attracted extensive attention.However,current Ga₂O₃ power devices still suffer from low breakdown voltage,large leakage current,and significant self-heating effects.Based on this,this study uses numerical simulation tools to investigate the breakdown performance of field-plate-connectedβ-Ga₂O₃ MOSFET and Ga₂O₃-on-Si C MOSFET and compares them with conventionalβ-Ga₂O₃ MOSFET,obtaining better electrical performance.The main work is as follows:The numerical calculation ofβ-Ga₂O₃ lateral MOSFET is calibrated.By researching the material properties of gallium oxide,a comprehensive gallium oxide simulation model parameter library is established,and the transfer characteristics of theβ-Ga₂O₃ MOSFET are studied using numerical calculation methods.The results show a high degree of agreement with experimental results.Based on this,an avalanche model parameter library for gallium oxide is established,and by optimizing the simulation convergence at low intrinsic carrier concentration,the breakdown voltage of different active layer concentrations is obtained,which is in good agreement with the experimental results,thus validating the accuracy of the establishedβ-Ga₂O₃ MOSFET device simulation model.The novel field-plate structure forβ-Ga₂O₃ MOSFET is proposed.By analyzing the electric field distribution in the channel,it is found that the peak electric field of theβ-Ga₂O₃ MOSFET concentrates at the gate edge.To optimize this,a gate field-plate structure is proposed,and the effects of the gate field-plate length(L_FP)and passivation layer thickness(T_FP)on the breakdown voltage of the device are studied.The optimal parameters for the gate field-plate structure are determined as L_FP=3.0μm and T_FP=0.5μm,increasing the breakdown voltage of the device from449 V to 1060 V.To further improve the breakdown voltage of the device,the discrete field-plate structure is proposed based on the gate field-plate structure.The optimal parameters for the discrete field-plate structure,including the discrete field-plate length(L_DFP),passivation layer thickness(T_DFP),and distance between the discrete field-plate and gate field-plate(D_DFP),are obtained through optimization.The breakdown voltage of the device is further increased to 1269 V.The self-heating effect of theβ-Ga₂O₃ MOSFET is studied,and the novel structure of Ga₂O₃-on-Si C MOSFET is proposed.By comparing the transfer characteristics and output characteristics of the conventionalβ-Ga₂O₃ MOSFET and Ga₂O₃-on-Si C MOSFET through simulations,it is found that the lattice temperature of Ga₂O₃-on-Si C MOSFET decreases by more than 100°C and the drain current increases by 95%,effectively alleviating the self-heating effect of theβ-Ga₂O₃ MOSFET.In addition,the premature breakdown phenomenon of Ga₂O₃-on-Si C MOSFET is studied,and the breakdown characteristics of the two are compared.It is found that the Si C substrate surface reaches the critical breakdown field strength first,and an over 40%decrease in breakdown voltage is observed in the unoptimized Ga₂O₃-on-Si C MOSFET.By optimizing the epitaxial layer concentration and thickness and the substrate concentration and thickness,the optimal structural parameters are determined as an epitaxial layer concentration of 10¹⁷ cm^-3,thickness of 235 nm,substrate doping concentration of 10¹² cm^-3,and thickness of 30μm.The breakdown voltage of the device is 1057 V,which is minimizing the decrease to the maximum extent compared to the conventionalβ-Ga₂O₃ MOSFET.