Optimization of GaAs PIN diodes for neutron detection

GaAs-based PIN detectors with mesa sizes 1, 2.5, 5, 7.5 and 10 mm were fabricated and characterized for alpha particle response using a Po-210 alpha source. By decoupling the neutron conversion process of a proximity moderator, we were able to directly probe the alpha response characteristics of the PIN detectors as a function of device area. Dark current levels in the PIN detectors ranged from 6.1 to 9.5 pA at zero bias. The dark current values were higher for larger devices and a linear relationship between mesa size and dark current was observed. The PIN detectors were found to have a strong alpha response of up to 5 nA/mm2 with a linear relation between the response current and mesa area. The measured responsivity of the detectors was 0.014 A/W. The average device efficiency was determined to be 31.5%. Using the measured alpha response properties of the GaAs PIN diodes one is able to select the optimal device area for a given moderator and application specific neutron flux.