Size dependent polaritonic effects in GaN microrod studied through optical property investigation

We have investigated the optical properties of gallium nitride microrods systematically by spatially resolved cathodoluminescence, Raman and photoluminescence measurements. Blueshifting in near band gap energy with the decrease in diameter of studied microrods has been observed from cathodoluminescence and is attributed to the formation of whispering gallery mode polaritons in microrod cavity. Raman spectra along the length of the tapered microrod shows no noticable shifting in Raman mode positions confirm that the band gap energy changes with the decrease in diameter is not due to the stress/strain or different doping concentration. PL was carried out to look at the probable possibilities of polariton formation in microrod cavity. Exciton photon coupling strength depends on the diameter of the microrods and the coupling strength decreases with the decrease in diameter as studied from spatial-resolved photoluminescence spectra. Rabi splitting energy of nearly 300 ± 40 meV and so polariton lasing was observed from the wide end but that gradually decreases with the decrease in diameter.