Irradiation Response of Graphene Enhanced Gallium Nitride Metal-Semiconductor-Metal Ultraviolet Photodetectors

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 metal-semiconductor-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 current-voltage 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.

Irradiation effects of graphene-enhanced gallium nitride (GaN) metal-semiconductor-metal (MSM) ultraviolet photodetectors

“…Graphene is optically visible on particular SiO 2 thicknesses, 22 so the SiO 2 could provide rapid feedback on the graphene transfer process. In our previous work, 16 the graphene-on-SiO 2 stack provided an optical approach to confirming the successful transfer and etching of graphene relative to the substrate, but device performance suffered from trapped charges generated in the irradiated SiO 2 layer upon gamma irradiation. Here, the SiO 2 layer beneath the photodetector active area was now removed to mitigate those effects and allow direct graphene-to-GaN contact in that region.…”

“…The removal of the SiO 2 layer beneath the graphene electrodes has improved the responsivity and PDCR values by an order of magnitude compared to previous results. 16 Nitrided oxides, aluminum or hafnium oxide thin films, which have been shown to shift threshold voltages for radiation-hardened metaloxide-semiconductor (MOS) devices, 30 should be evaluated as barrier layers underneath the bus bar regions to mitigate dark current leakage due to irradiation. The microstructural evolution of the graphene, barrier layer, and GaN microstructural evolution due to irradiation should be further investigated using high-resolution microscopy and spectroscopy methods.…”

“…In our previous work, we showed that GaN MSM photodetectors could perform up to 50 krad TID 15 and that graphene MSM electrodes on hybrid silicon dioxide/GaN substrates could function up to 200 krad TID. 16 In the latter case, trapped charges generated in the irradiated SiO 2 thin film seemed to affect device performance by saturating the photocurrent, so here attempt to mitigate those effects with direct contact of graphene and GaN devices. Since space satellite components have been shown to fail at less than 25 krad TID, 17 devices that can perform robustly under harsh environmental conditions at greater than 25 krad TID are beneficial.…”