Graphene-enhanced gallium nitride ultraviolet photodetectors under 2 MeV proton irradiation

The electrical characteristics of gallium nitride (GaN) ultraviolet (UV) photodetectors with graphene and semitransparent Ni/Au electrodes subjected to 2 MeV proton irradiation are reported and compared. Graphene is shown to have a very high transmittance (87%) in the UV regime (365 nm) compared to semitransparent Ni/Au (3 nm/10 nm) films (32%). Correspondingly, microfabricated graphene/GaN photodetectors showed a much higher pre-irradiation responsivity of 3388 A/W, while that of semitransparent Ni/Au/GaN photodetectors was 351 A/W. For both types of electrodes, intermittent current-voltage measurements performed during 2 MeV proton irradiation showed minimal variation up to a fluence of approximately 3.8 × 10¹³ cm^-2. Additionally, Raman spectroscopy of 200 keV proton beam, 3.8 × 10¹³ cm^-2 irradiated graphene showed minimal disorder with only a 6% increase in I_D/I_G compared to pre-irradiated graphene. These results support the use of graphene-enhanced GaN UV photodetectors in radiation-rich environments such as deep space.