Photoluminescence Measurement on Low-temperature Metal Modulation Epitaxy Grown GaN

A low-temperature photoluminescence (PL) study was conducted on low-temperature metal modulation epitaxy (MME) grown GaN. By comparing the PL signal from high temperature grown GaN buffer layers, and MME grown cap layers on top of the buffer layers, it was found that MME grown GaN cap has a significantly greater defect-related emission. The band edge PL from MME grown GaN found to be 3.51eV at low temperature. The binding energy of the exciton in GaN is determined to be 21meV through temperature dependence analysis. A PL peak at 3.29eV was found in the luminescence of the MME grown cap layer, which was not observed before. The thermal activation energy of this peak is determined to be 33meV. Emission at this energy in previous GaN material has been shown to be the result of stacking faults. We believe this peak in the MME GaN is also the result of stacking faults. In droplets were used as a surfactant to improve the quality of MME grown GaN. By comparing the PL signal from samples with and without In surfactant, it was found the 3.29eV PL peak disappears with the use of In droplet, which indicates the surfactant effect of In droplet has reduced the formation of these stacking faults.