p-Type Behavior of Carbon on n-Type GaN Schottky-Barrier Diodes Doped by Neutron Transmutation Effects

Altered doping profiles of gallium nitride (GaN) have been studied by using different doping conditions of the neutron transmutation process in two different irradiation areas in the reactor: dominant epithermal neutron (DEN) area and dominant thermal neutron (DTN) area. We measured the variation in irradiation byproducts and studied its influences. The doping concentration of Ge isotopes produced during the irradiation was measured by gamma-ray spectroscopy counting and compared with data measured by secondary-ion mass spectroscopy (SIMS). We found that under different irradiation conditions, the concentration ratio of 14C–Ge significantly got reduced from 50% in the DTN area to 6.6% in the DEN area. The data from photoluminescence (PL) spectrums with the increased peak of the redshifted yellow luminescence (YL) band and intensity difference indicate that 14C may behave as a p-type dopant. To study variations of the electrical properties depending on the amount of 14C, we designed and fabricated the Schottky-barrier diodes (SBDs) with neutron-irradiated GaN samples. The significant reduction of 14C-to-Ge ratio turned out to enhance the electrical characteristics. Furthermore, junction resistance confirmed the p-type behavior of 14C.