Reducing the efficiency droop by lateral carrier confinement in InGaN/GaN quantum-well nanorods

Abstract

Efficiency droop is a major obstacle facing high-power application of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs). In this paper, we report the suppression of efficiency droop induced by the process of density-activated defect recombination in nanorod structures of a-plane InGaN/GaN QWs. In the high carrier density regime, the retained emission efficiency in a dry-etched nanorod sample is observed to be over two times higher than that in its parent QW sample. We further argue that such improvement is a net effect that the lateral carrier confinement overcomes the increased surface trapping introduced during fabrication.

Lateral carrier confinement in InGaN quantum-well nanorods

“…4(b)). The above results strongly support the notion that the lateral carrier diffusion has been suppressed in [14]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)…”

“…The effect of reducing carrier diffusion in nanorod structures has also been observed in nonpolar QW samples [14]. The process of thermally-activated lateral carrier diffusion also leads to a delayedrise component in a time scale of hundreds of picoseconds.…”

“…The InGaN/GaN nanorods were fabricated from the QW LED structure by inductively-coupledplasma etching using a novel etch mask of self-assembled indium tin oxide (ITO)-based nanodots [14,39,48]. By controlling the size of the ITO-based nanodots and the ICP etching conditions, nanorod samples with radius of ∼130 nm and ∼50% filling factor were fabricated successfully.…”

“…Nevertheless, surface states introduced during the nanofabrication have been a long-standing issue that existed in such technology [12,47,49]. In our previous study, the lifetime of polar c-plane nanorods is much shorter than its parent QWs, indicating the etch-induced surface states provide additional channels for carrier recombination [14]. Unlike the huge difference observed in PL lifetime between nanorods and the parent QWs with polar structures, the lifetime of PL decay in the nanorod sample (∼0.56 ns) is very close to the value in the parent QW sample(∼0.58 ns) (Fig.…”

“…Nonetheless, the problem of ''efficiency droop'', i.e., the decrease in quantum efficiency of a LED with increasing carrier density, has persisted since the early demonstration of nitride LEDs in 1990s [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. It becomes even worse with LEDs operating at longer wavelengths (i.e., >500 nm) [19,32], making it challenging to obtain highly efficient white-light emission with nitrides for high power applications.…”