Low energy electron beam irradiation of gallium nitride

In this work, the behavior of gallium nitride and indium gallium nitride under low energy electron beam irradiation (LEEBI) has been investigated. Furthermore, a periodic silver grating has been investigated and fabricated with the aim of obtaining plasmonic coupling based luminescence enhancement from a light emitting structure. The effect of the silver grating and LEEBI were both studied using photoluminescence (PL) measurements and the silver grating properties were also investigated using reflectometry. It has been observed in this work that LEEBI causes significant degradation of band-edge (BE) luminescence in metal-organic vapor phase epitaxy (MOVPE) grown InGaN quantum well (QW) structures and GaN films. The degradation increases with increasing LEEBI dose (charge per surface area). Moreover, the PL intensity decreases faster with smaller kinetic energy of electrons. This in agreement with the electron beam energy dissipation profile in GaN. The mechanism of the BE luminescence degradation has been studied with positron annihilation spectroscopy (PAS). The measurements reveal that LEEBI is able to activate in-grown gallium vacancies (VGa) in GaN, which are otherwise passive, i.e., neutral through the band gap and invisible to PAS. The mechanism for the passivation of the VGa is the formation of vacancy - hydrogen complexes, especially VGa - 3H. Hence, LEEBI treatment can probably remove hydrogen from these complexes making them active. Moreover, LEEBI induced optical degradation was measured to be virtually identical for samples grown in both hydrogen and nitrogen environments. Also, a partial recovery of the BE emission was obtained with thermal annealing. This suggests internal migration of H, partially refilling the vacancy sites. A silver nano-grating structure covered with (poly)vinyl alcohol (PVA), deposited on top of an InGaN QW structure, was developed. The buried metal grating can diffract light from the optical modes propagating in GaN and PVA. This simple technique has already yielded emitted light intensity almost 3-fold the original.