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GaN Avalanche Devices for RF Power Generation


Radio Frequency (RF) power generation by diode sources enables compact and affordable sources for a wide range of sensor applications. Avalanche breakdown is an important mechanism for the generation of RF power in a two terminal diode. Examples are IMPact ionization Avalanche Transit Time (IMPATT) diodes demonstrated in Silicon, Gallium Arsenide (GaAs), and Indium Phosphide (InP). By both thermal considerations and large breakdown field, Gallium Nitride-based avalanche devices should offer a substantial advance (~100X) in power output with improved efficiency (~2X). The problem in wide bandgap nitrides is that until recently, avalanche breakdown has not been experimentally observed, despite two decades of material advances. The absence of experimental observation is often attributed to the higher dislocation density of current GaN technology, which lowers the breakdown electric field threshold due to non-avalanching mechanisms. Recently there are reports of the observation of avalanche-breakdown-like behavior in GaN devices for power electronics, where avalanche breakdown phenomena are exploited to prevent device burnout. No RF devices have been developed to exploit the avalanche behavior. The goal of this topic is to demonstrate RF power generation in Gallium Nitride or related group III-Nitride diodes exploiting avalanche breakdown. PHASE I: Determine feasibility of exploiting avalanche breakdown in the III-Nitride system in a representative diode structure for RF power generation. Demonstrate avalanche gain behavior with a diode in a representative circuit. Design the required device geometries and material properties for W-band operation along with the expected power output and DC conversion efficiency, based on the current state of the art for high quality GaN materials and prior theoretical work on scaling studies of microwave diodes and material properties of GaN. The planned device should be capable of operation up to a nominal current density of 100,000 A/cm2 . PHASE II: Develop and demonstrate the device design formulated in Phase I. Fabricate the device with the appropriate GaN material technology, processing, and geometry to demonstrate RF power generation at a nominal frequency of 94 GHz in an appropriate circuit. Characterize the device performance as a function of DC operating parameters, circuit matching, and thermal effects. A fixtured device with waveguide output will be delivered to the government for validation along with test data detailing the device performance. Based on the measured device performance and scaling considerations, estimate expected performance for Ka-, and G-band operation. PHASE III: Develop an RF source module based on the Phase II results for compact payloads for expendable decoys. Phase III should optimize power output and efficiency and develop device packaging that minimizes device heating through thermal management approac

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