Leakage Current and Breakdown Characteristics of Isolation in Gallium Nitride Lateral Power Devices

In gallium nitride (GaN) lateral power devices with advanced E-field management, isolation becomes a bottleneck for achieving higher breakdown voltage (BV). To understand the physical mechanism of isolation, the experimental analysis of isolation structures is done in this work. This article presents the measured leakage current and breakdown characteristics of isolation structures, compatible with lateral devices. For unimplanted isolation structures, leakage is injection barrier limited and breakdown is by surface punchthrough. BV has a quadratic dependence on the isolation length. Ion implantation introduces trap-limited hopping conduction, marked by the exponentially field-dependent conductance. After implantation, despite an increase in leakage current, BV increases drastically. The dependence of BV on isolation length changes from quadratic in unimplanted isolation to linear in implanted one due to flattening of E-field. To achieve high BV in GaN lateral power devices, the implanted isolation structure is preferred at the cost of high isolation leakage.