Research On GaN-based Recessed Anode Schottky And PiN Diodes

With the increasingly severe international situation,electronic warfare has become the military focus of various countries,and the radar equipment,which is the core of our detection,is extremely vulnerable to being blinded by the high-power microwave weapons,so it needs limit protection in the front part of the radar.However,the traditional limiting modules mainly based on Si and Ga As diodes have faced bottlenecks and are difficult to meet the needs of high-power applications.As a typical representative of the third-generation semiconductor,gallium nitride（GaN）has unique characteristics such as large forbidden band width,high breakdown field strength,high electron saturation drift speed,and the ability to form two-dimensional electron gas（2DEG）with high density and high mobility.The advantages of material characteristics are very suitable for application in high-power limiting technology.At the same time,thanks to the advantages of materials and various technological breakthroughs,such as the recessed anode structure effectively reduces the turn-on voltage,the anode treatment technology reduces the reverse leakage,and the field plate design further reduces the capacitance,etc.,AlGaN/GaN Schottky diodes have been widely used in recent years.It shows great potential in microwave and high-voltage high-power applications and is the device of choice for next-generation post-stage limiting.To further advance the maturity of AlGaN/GaN Schottky diodes,in-depth studies of their intrinsic physical mechanisms are required to improve device reliability and move closer to ideal diode characteristics.On the other hand,with the advancement of epitaxy technology,the research on GaN PiN diodes has gradually increased.As a direct bandgap and wide-bandgap semiconductor material,the PiN diodes have better frequency characteristics and larger power capacity,and are suitable for use as front-ends of high-power diodes in limiter circuits.Under this research background,this paper optimizes the structure design and fabrication process of GaN diode devices suitable for microwave limiting applications,and deeply studies the device transport mechanism.The main achievements are as follows:1.It is found through experiments that recessed anode GaN Schottky diodes have lower dislocation sensitivity,and proposed a barrier height regulation model of field plate recessed anode Schottky diodes,proving that the new recessed anode Schottky diodes Diodes have more superior characteristics.First,the advantages of recessed anodes compared to traditional planar anode diodes were explored.The electrical properties of laterally recessed anodes and traditional planar anode AlGaN/GaN Schottky diodes were compared experimentally on epitaxial substrates with different dislocation densities.The anode structure has low sensitivity to dislocations in epitaxial materials.Secondly,the recessed anode GaN Schottky diode fabricated with the same epitaxial material has lower turn-on voltage,higher forward current density,lower reverse leakage,and higher breakdown voltage,which is closer to the ideal Schottky diode.Finally,the Schottky barrier regulation model of recessed anode AlGaN/GaN Schottky diode with field plate is proposed by theoretical calculation and correction of mirror force model.The forward current calculated by the model is compared with the actual measured results,which verifies the accuracy of the model.Through the research in this chapter,the unique advantages of the recessed anode structure are explained,which lays a theoretical foundation for the development of high-frequency high-power GaN Schottky diodes.2.The physical mechanism of reverse leakage of recessed anode AlGaN/GaN Schottky diodes is studied,and a three-region leakage mechanism model is proposed,which can accurately characterize the leakage law.In order to further study the reverse leakage mechanism of recessed anode AlGaN/GaN Schottky diodes,diodes with different R_A and L_overlap were prepared experimentally,and the reverse leakage was found to increase significantly with the increase of L_overlap through comparison.According to the difference in the trend of the diode temperature changing I-V curve,the reverse leakage mechanism of the diode is discussed in three areas.At near zero bias,thermionic emission is the dominant mechanism,and electrons directly enter the channel by crossing the Schottky barrier to form reverse leakage.As the reverse bias voltage increases,the potential barrier increases,and electrons undergo Frenkel-Poole emission through the trap level into the semiconductor.When the reverse current is almost constant with the increase of reverse bias voltage,the trap-assisted tunneling mechanism of the AlGaN surface becomes dominant,and electrons directly tunnel into the semiconductor through the trap.According to the above research,a three-region leakage model of recessed anode AlGaN/GaN lateral Schottky diode is proposed,and the accuracy of the model is verified by comparing with the experimental results,and the positioning analysis of the reverse leakage path of the device is provided.When the reverse bias voltage is close to the breakdown voltage,the electrons directly gain energy and tunnel through the barrier to form a reverse leakage current that continues to increase as the voltage increases.3.A GaN MIS diode with low turn-on voltage,low leakage and low subthreshold swing is proposed and realized.In order to break through the contradictory relationship between the low turn-on voltage and low leakage of Schottky diodes,the MIS diode structure was innovatively adopted,and the high-quality Al₂O₃ dielectric layer was obtained by optimizing the ALD-Al₂O₃ growth process and using ozone as the oxygen source.Using surface solution treatment and annealing technology,the interface treatment process between Al₂O₃ and non-polar GaN is further optimized,and the optimization mechanism is further analyzed.The interface state density of ALD-Al₂O₃ and a-plane GaN MOSCAP treated with piranha solution,BOE solution and N₂ PDA was measured by UV-assisted C-V method as low as2.04×10¹¹ cm^-2·e V^-1,which is the best international index.Utilizing this structure in a recessed anode yields a novel GaN MIS with turn-on voltage as low as 0.32 V,reverse leakage at room temperature as low as 4.5×10^-4 m A/mm,and subthreshold swing at room temperature as low as 10 m V/dec diode.The current transport mechanism of the MIS diode is the superposition of thermionic emission and direct tunneling,and the model is highly consistent with the actual test results.4.Designed and implemented a low on-resistance,high-power GaN PiN diode.Theoretical calculations were used to predict the carrier concentration in the i region under large injection of GaN PiN diodes.It was found that the lower the concentration and the smaller the thickness of the i region,the better the conductance modulation characteristics.And through theoretical calculation,it is found that the bulk resistance of the self-supporting substrate is very large,and the theoretical resistance value can be as low as 0.066 mΩ·cm²by adopting the quasi-vertical structure,which is 12%of the full vertical structure.The ohmic contact process of the GaN PiN diode is optimized through experiments,and the ohmic contact resistance of 60Ω·mm is obtained,which is on par with the international index of the same period.The isolation depth of the PiN diode and the post-etching process are optimized,so that the reverse leakage of the diode within-20 V is as low as 1×10^-7 A/cm².Finally,a high-power GaN PiN diode with a forward current exceeding 1×10⁴ A/cm²,a resistance as low as 0.1 mΩ·cm²,an on-off ratio as high as 10¹⁰,and a breakdown voltage of 200 V was fabricated.5.Developed a high Al composition AlGaN Schottky diode with a breakdown voltage exceeding 2 k V.For the development of next-generation high-power diode material devices,Si-doped Al_0.85Ga_0.15N epitaxial wafers were prepared on sapphire substrates,and 15%GaN was innovatively introduced to make the epitaxial wafers obtain a free electron concentration of 2×10¹⁷ cm^-3 case,the surface roughness is as low as 0.33 nm.The ohmic contact process of the high Al composition material was optimized,so that the contact resistance of the device was reduced to 7.5 kΩ?mm,and the surface state was reduced by etching the anode to improve the Schottky contact of the device.The Al_0.85Ga_0.15N Schottky diode prepared with this epitaxial wafer has a breakdown voltage of 2 k V when the cathode-anode spacing is 17μm,and achieves a very low ideal factor of 2.3 greater than 5.And the forward current of the existing international high Al composition diode is increased from 0.1 A/cm² to 1.2A/cm².This study illustrates the great promise of using high Al_xGa_1-xN for next-generation power devices.