Neutron radiation hardness of aluminum gallium nitride UV LEDs at various wavelengths

Abstract

Radiation hard diagnostics are critical to the success of nuclear fusion at National Ignition Facility, Z, ITER, and prolonged space explorations. We have first demonstrated the exceptional proton radiation hardness of initial GaN devices and qualified their space flight and deployment for missions such as the Laser Interferometer Space Antenna and International Space Station. We have further conducted neutron radiation hardness experiments at Los Alamos Neutron Science Center by opening a new high fluence beam station. During 2014-2016, we irradiated multiple Aluminum Gallium Nitride (AlGaN) LEDs with a maximum fluence of 2.4 × 1013 neutrons/cm2 in 3 years and generated 54 161 current-voltage (I-V) scan traces. Our data processing program analyzes each and all I-V traces. In addition, we retrieved local temperature records to analyze and remove temperature effects in the outdoor environment. The I-V curve families of AlGaN UV LEDs with emitting wavelengths of 265, 275, and 310 nm were compared. The I-V curves of 265 nm AlGaN UV LEDs have the smallest deviations from the average value, while the I-V curves for 310 nm AlGaN LEDs showed the largest deviations from the average value. We have reached another important recommendation for the optimal use of multiple AlGaN optoelectronic devices or imaging arrays for inertially confined fusion diagnostics: Shorter wavelength devices at 265 nm exhibit more consistent radiation hardness performance than the 310 nm devices. Higher aluminum content LEDs or AlxGa1-xN devices with higher mole fraction x for generating shorter wavelengths have better radiation hardness for fusion diagnostics.