Investigation of low-temperature electroluminescence of InGaN/GaN based nanorod lightemitting arrays

Abstract

For InGaN/GaN based nanorod devices using a top-down etching process, the opticaloutput power is affected by non-radiative recombination due to sidewall defects (whichdecrease light output efficiency) and the mitigated quantum confined Stark effect (QCSE)due to strain relaxation (which increases internal quantum efficiency). Therefore, theexploration of low-temperature optical behaviors of nanorod light emitting diodes(LEDs) will help identify the correlation between these two factors. In this work,low-temperature electroluminescent (EL) spectra of InGaN/GaN nanorod arrays wereexplored and compared with those of planar LEDs. The nanorod LED exhibits amuch higher optical output percentage increase when the temperature decreases.The increase is mainly attributed to the increased carriers in the quantum wellsfor radiative recombination. Also, due to a better spatial overlap of electronsand holes in the quantum wells, the increased number of carriers can be moreefficiently recombined in the nanorod device. Next, while the nanorod array showsnearly constant peak energy in the EL spectra at various injection currents at thetemperature of 300 K, a blue shift has been observed at 190 K. The results suggest thatwith less non-radiative recombination and thus more carriers in the quantumwells, carrier screening and band filling still prevail in the partially strain relaxednanorods. Moreover, when the temperature drops to 77 K, the blue shift of bothnanorod and planar devices disappears and the optical output power decreasessince there are fewer carriers in the quantum wells for radiative recombination.