Efficiency droop and carrier transport in AlGaN epilayers and heterostructures

Abstract

The photoluminescence (PL) spectroscopy of AlGaN epilayers and heterostructures under quasi‐steady‐state conditions at different excitations in a wide temperature range from 8 to 300 K established the connection between the internal quantum efficiency, efficiency droop, and carrier localization. The carrier localization conditions were estimated from the temperature dependences of the PL band peak positions. The temperature dependences of the PL intensity were fitted using the Arrhenius‐type equation with two activation energies, which were attributed to the carrier redistribution within the localized states and carrier delocalization, respectively. The delocalization of the localized carriers affects the luminescence efficiency via the enhancement of the two mechanisms of opposite signs: the bimolecular radiative recombination and nonradiative recombination due to an increased probability to reach nonradiative recombination centers.

Effects of Nanoscale V-Shaped Pits on GaN-Based Light Emitting Diodes

“…Furthermore, an opposite trend could be observed between droop onset and IQE. In the previous research, lower efficiency droop onset can be attributed to stronger carrier localization, caused by both content fluctuations and QW width fluctuations [ 42 ]. Besides, the fluctuation and higher localization effect can prevent the carrier diffusion to the extended defects and contribute to a mitigation of the droop effect [ 43 ].…”

Origin of thermal quenching of exciton photoluminescence in AlGaN epilayers

“…3) implying involvement of two nonradiative channels with activation energies of 6 and 69 meV. These channels might be tentatively attributed to the exciton redistribution within the localized states and exciton delocalization to the mobility edge, respectively [9].…”

“…where I 0 is the low-temperature PL intensity, c i and E Ai are the rate constant and activation energy of the ith process, and i is the number of nonradiative recombination channels, typically ranging from 1 to 3 [1][2][3][4][5][6][7][8][9]. The thermally-activated mechanisms responsible for the PL quenching are usually related to the thermal dissociation of free or bound excitons [1][2][3], escape of carriers out of a quantum well [3,4], transfer of carriers over a barrier to nonradiative recombination centres [5,6], and thermal activation of localized carriers [4,[6][7][8][9].…”

“…The mechanism of carrier delocalization is commonly used to interpret the PL temperature dynamics in materials having a large density of localized states, e.g. ternary nitride alloys, InGaN [6,7] and AlGaN [8,9]. However, a few distinct activation energies are hardly compatible with a wide and continuous energy distribution of localized states.…”