Reliability Study And Anode Structure Optimization Of AlGaN/GaN Schottky Barrier Diodes

GaN-based III-nitride wide bandgap semiconductors are considered as highly promising materials for next-generation power electronic devices due to their outstanding properties such as high electron mobility,high critical electric field and high thermal conductivity.GaN-based Schottky barrier diode(SBD)is an indispensable component in power electronic circuits,being used in various converters and inverters.Al GaN/GaN hetero-structure based lateral SBDs are therefore of extensive research interest considering the existence of their high density and high-mobility two-dimensional electron gas(2DEG)as well as their high breakdown electric field over3MV/cm.In addition,the fabrication process of Al GaN/GaN-based SBDs is compatible with that of GaN high-electron-mobility transistor(HEMT),showing great promise for versatile and compact GaN power integrated circuits(ICs).Although the techniques of GaN lateral SBDS have been improved remarkably,their current performance is still far from the theoretical limit.The main performance problems of GaN SBDs include high V_on and R_on,low breakdown voltage,and poor uniformity.In this thesis,in order to improve the performance of GaN lateral SBDs,two innovative device structures are proposed and fabricated,and then their electrical characteristics are systematically studied.The main contents of this thesis are as follows:1.In this work,multi-aperture anode structure with fully recessed Al GaN barrier layer was proposed to obtain a low V_on and R_on without sacrificing the reverse blocking capability.With the Schottky junction formed between the Ni anode metal and the channel of two-dimensional electron gas,as well as the evidently enlarged contact profile by the introduction of multiple apertures,the Schottky barrier height is successfully lowered to 0.46 e V and the V_on is lowered to 0.35V.The on state resistance decreases linearly with the increase of the perimeter of Schottky contact sidewall.An optimal value of 6.93m?·cm² is obtained.The relationship between anode etching depth and forward characteristics is studied.It is found that the fully recessed multi-aperture anode configuration could provide additional advantage in device uniformity.Lastly,Ti/Al/Ni/Au cathode fabricated with low temperature-annealing process is beneficial for obtaining 2700V reverse breakdown voltage because of the low contact surface roughness,leading to a power figure-of-merit of 1.11GWcm^-2.2.To further improve current density and study the performance of packaged GaN devices,multi-finger fully-recessed SBDs and dual-anode SBDs were proposed.Compared with fully-recessed devices,the dual-anode SBDs exhibit lower V_on of0.44V and lower R_on of 3.28 m?·cm² owing to their unique current conducting mechanism.On the other hand,the dual-anode SBDs exhibit a relatively poorer forward current uniformity,which should be attributed to the variation in the recess etching depth.The leakage current is found non-sensitive to temperature,which could be explained by direct tunneling mechanism.Finally,the flip-chip packaging is confirmed to have better heat flux distribution as compared to that of conventional wire bonding based packaging,which enables higher surge current capability.