Optimization Of GaN Vertical Junction Barrier Schottky (JBS) Diodes

Semiconductor power devices have the ability to handle high voltages and large currents,and can be applied to power electronic systems to realize the role of voltage change,voltage withstand,rectification and current renewal.Therefore,power devices have very important practical application value and theoretical research significance.As an important branch in the field of power devices,Schottky barrier diodes(SBDs)are an important part of power electronic systems,playing an important role in rectification and voltage withstanding.Gallium nitride(GaN)materials have excellent properties such as wide band gap,high critical electric field and high electron mobility,which are excellent materials for the preparation of high-power devices.Among them,GaN vertical SBD has become the preferred device structure for modern power systems due to its low on-state voltage drop,fast switching speed and low reverse recovery loss.Due to the influence of the mirror force between the anode metal and the semiconductor under reverse bias,the strong electric field at the Schottky contact interface concentrates resulting in a reduction of the Schottky barrier,so the SBD exhibits a lower reverse breakdown voltage and a larger reverse leakage current.The degree of Schottky barrier reduction due to the mirror force is directly related to the electric field on the Schottky contact surface,and several device structures have been proposed to suppress the strong electric field on the Schottky contact surface,one of which is a typical junction barrier Schottky(JBS)diode.The principle of JBS diode is to regulate the electric field distribution by alternating PN junctions below the anode contact,that is,the depletion area formed between adjacent PN junctions overlap to produce an "equivalent potential barrier",the barrier can be achieved for Schottky surface electric field shielding.In general,the depth of the PN junction in a JBS diode is positively correlated with the effectiveness of shielding the surface electric field,and a thicker p-type region is required to achieve a deeper PN junction.However,the doping of the p-type region is usually achieved by ion implantation,and the thicker the p-type region,the higher the ion implantation energy is required,which introduces more unwanted impurities and defects in the material and thus has a significant impact on the device performance.In this thesis,the device structure design is used to optimize this study.(1)A GaN-based trench-type JBS(TJBS)diode structure is proposed and designed,which can obtain a deep PN junction interface and optimize the electric field distribution inside the device.At the same time,the TJBS structure is systematically studied,the influence of key structural parameters on the forward and reverse performance of the device is analyzed,and a forward pass analysis model is established,and the validity of the model is verified by fitting the calculated and simulated values.(2)To further enhance the reverse breakdown performance of the TJBS structure,GaNbased superjunction TJBS(SJ-TJBS)diodes are proposed and designed,using oxide to fill the trench to achieve the depletion effect of the superjunction,and the breakdown voltage of SJTJBS diodes is significantly enhanced compared to the TJBS structure.A systematic study of SJ-TJBS diodes was then performed,including the effect of key structural parameters on the forward and reverse static performance of the device and the effect of trench shape on the reverse recovery of the device.The highest quality factor(FOM)value obtainable for the device is 8.65 KV2/mΩ·cm2.Finally,the designed SJ-TJBS diode demonstrates performance advantages when compared with the breakdown voltage and on-resistance of the same type of devices reported in the literature.