Irradiation Response of Graphene Enhanced Gallium Nitride Metal-Semiconductor-Metal Ultraviolet Photodetectors
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Irradiation Response of Graphene Enhanced Gallium Nitride Metal-Semiconductor-Metal Ultraviolet Photodetectors Heather C. Chiamori1, Nicholas Broad2, Chetan Angadi3, Ruth Miller1, Caitlin Chapin4, Ateeq Suria4, Sharmila Bhattacharya3 and Debbie G. Senesky1,2 1 Aeronautics & Astronautics Dept., Stanford University, Stanford, CA 94305, U.S.A. 2 Electrical Engineering Dept., Stanford University, Stanford, CA 94305, U.S.A. 3 NASA Ames Research Center, Moffett Field, CA 94035, U.S.A. 4 Mechanical Engineering Dept., Stanford University, Stanford, CA 94305, U.S.A. ABSTRACT Radiation-tolerant materials, sensors and electronics can enable lightweight space subsystems with reduced packaging requirements and increased operation lifetimes. Such technology can be used within extreme harsh environments related to space exploration, radiation medicine and power generation (combustion and nuclear). Gallium nitride (GaN), a ceramic semiconductor material, is a candidate material due to its stability within high-radiation, high-temperature and chemically corrosive environments. In addition, the wide bandgap of GaN (3.4 eV) can be leveraged for ultraviolet (UV) wavelength photodetection. In metalsemiconductor-metal (MSM) photodetector architectures using Schottky contacts, transparent electrodes (e.g., graphene) can increase sensitivity and improve overall device response. Here we present fabrication and characterization of GaN-based UV photodetectors using graphene electrodes irradiated up to 200 krad total ionizing dose (TID) then tested under UV light and dark conditions. For current-voltage measurements taken at 90, 120 and 200 krad TID, the currentvoltage response does not vary significantly. From 90 to 120 krad TID, the responsivity shifts by 2% before dropping off at 200 krad TID. These initial findings suggest that graphene/GaN MSM UV photodetectors can provide robust operation within extreme harsh environments. INTRODUCTION Radiation-hardened materials and electronic devices can benefit extreme harsh environment applications such as space exploration, radiation medicine and power generation (combustion and nuclear) by enabling monitoring and control. Gallium nitride (GaN) is a candidate material for such applications since it has exhibited radiation-hard behavior due to its wide bandgap (3.4 eV), high atomic binding energy (18 to 28 meV) and ability to withstand various temperature excursions and chemically corrosive environments [1]-[5]. Additionally, GaN has shown high ionic bond strength and large crystal density, properties that indicate GaN may be less influenced by interstitial impurities [6]. A high displacement energy for the Ga atom was experimentally determined as 19 ± 2 eV, a value comparable with silicon carbide and higher than silicon and gallium arsenide [2]. Only carbon showed a significantly higher displacement energy [2] which warrants the exploration of carbon-based materials in the design of radiation-hardened electronics. Graphene is a two-dimensional monolayer of carbon atoms arranged in a honeycomb confi
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