The Study Of Hybrid-Anode AlGaN/GaN Schottky Diode

Recently,AlGaN/GaN heterostructure Schottky diodes are of great importance in power switching applications,and they can fast switching speed,high electric field breakdown strength,and good thermal properties.However,Ga N-based Schottky diode has a relatively high turn-on voltage.The hybrid structure is composed of recessed Schottky and ohmic contact,and has a better gate control function.The turn-on voltage of the diode is only determined by the threshold voltage of the channel instead of the Schottky barrier,and thereby it can effectively reduce the device turn-on voltage.In the discussion,the hybrid-anode AlGaN/GaN SBD is comprehensively studied both in structural simulation and device fabrication.The research plans are as follows:First,the effect of anode recessed depth and Schottky/ohm(L_sc/d)ratio on device characteristics were analyzed by Silvaco-ATLAS simulation software,and the simulation results were used to determine the device structural parameters and guide the device layout design.Then the hybrid-anode AlGaN/GaN SBD was fabricated,and the DC characteristics of the device were performed.The influence trend of recessed depth and Lsc/d ratio on device characteristics is experimental verification.Finally,the effects of cathode and anode spacing,floating metal strips and Si N passivation layer on the device characteristics are analyzed.Compared with the conventional device structure,the excellent characteristics of the hybrid structure are highlighted.In the device simulation section,the voltage-current characteristics of the hybrid anode AlGaN/GaN SBD were studied by simulating different etching depths and Schottky/ohm ratios.The two-dimensional electron gas（2DEG）concentration decreases under the Schottky contact as the anode etching depth increase.The turn-on voltage increases first and then saturates.After the breakdown voltage increases rapidly to the maximum value,it remains basically constant.When the anode bias is applied and the recessed depth is less than 15nm,the 2DEG under the Schottky groove cannot be completely depleted.The cathode-anode ohmic regions are easily connected and the device voltage-current characteristic curve is similar to the ohmic characteristic.The forward characteristics at depths of 19nm and 24nm（completely etched）are basically the same.The electrons tend to pass through the Schottky metal rather than the ohmic metal in the hybrid structure.As the L_sc/d ratio increases,the device turn-on voltage and reverse breakdown also can increase first and then saturate.When L_sc gradually increases,the conductive channel is extended,and it causes an increase in the specific on-resistance.Thereby the device turn-on voltage increases accordingly.When L_sc is increased to be comparable to the spacing between cathode and anode,the increase in Schottky length has little effect on the forward characteristics of the device.When the Schottky length is greater than 2μm,the Schottky depletion region can effectively block the leakage channel of the Ga N buffer layer during reverse bias.The device breakdown voltage is maintained at about 600V.When the recessed depth is 16nm and the L_sc/d is 2/60,it can well meet the low turn-on voltage and high reverse breakdown.Completion of device fabrication and electrical test work,the test results and simulation conclusions are basically consistent which indicated the reliability of simulation.Later,the effect of different distances between cathode and anode on the device was studied.Although reverse breakdown gradually increased with increasing distance between the cathode and anode,the increment in breakdown voltage was small.When the length of Schottky is 2μm and 4μm respectively,the effect of the distance between the floating metal and the Schottky on the breakdown characteristics of the device was analyzed.When the distance is 6μm,the breakdown voltage is the highest.The reason of low breakdown rise is probably due to the interface leakage caused by Si N passivation.After removal of Si N passivation,reverse leakage current and the breakdown voltage of the device were effectively improved.Finally,the electrical parameters of conventional Schottky structure,recessed Schottky structure and hybrid-anode structure diodes are analyzed.It is proved that the Ga N-based diode of the hybrid-anode structure is superior to other types of devices in terms of low turn-on voltage and reverse breakdown.