Study On Breakdown Characteristics Of AlGaN/GaN Schottky Barrier Diodes Fabricated On Silicon Substrate

GaN is one of the most promising candidate materials for power electronics applications due to its superior material characteristics such as large bandgap, high breakdown electrical field, high electron saturation velocity, and the ability to form hetero-junctions with other Ⅲ-nitride materials. Recently, GaN grown on silicon substrate has drawn much attention. Compared with conventional sapphire substrate, the high thermal conductivity of silicon is highly desirable for power device applications. Meanwhile, high-quality Si substrate with large diameter can be easily obtained at low cost. However, growth of GaN on Si is difficult due to the large lattice and thermal mismatch between the two materials. In this work, we investigated the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes (SBDs) fabricated on silicon substrate.1. Firstly, AlGaN/GaN-based SBDs with various spacings between ohmic and Schottky contacts were fabricated on silicon substrate. The breakdown voltage (BV) of the SBDs first increases as a function of contact spacing and then tends to saturate at larger spacing. The saturation behavior of BV is likely caused by vertical breakdown through the intrinsic GaN buffer layer on silicon. Then, we studied the effect of SiO2 passivation on the breakdown characteristics of the SBDs. It is found that SiO2 passivations could enhance the BV of the SBDs and suppress the reverse leakage current at lower reverse bias.2. Then, we used EMMI measurement to verify the physical analysis of the breakdown modes. The devices under test were post-breakdown SBDs. Based on the conventional optical images and their corresponding EMMI images, we found that the hot spots of the SBDs with various contact spacings revealed different primary leakage path after the hard breakdown. Thus, the EMMI result agrees with the physical picture of horizontal breakdown at small electrode spacing and vertical breakdown at large electrode spacing.3. For comparative study, some passivated devices were further terminated by field plates. Field plate termination was found effective to enhance BV of the SBDs. A high BV of 600 V is obtained with a low on-resistance (RON) of 3.15 mΩ·cm2, yielding a power figure-of-merit (BV2/RON) of 114 MW/cm2.