Investigation of local tunneling phenomena in green InGaN‐based LEDs

Abstract

The tunneling radiative recombination in green InGaN based Light Emitting Diodes (LEDs) has been studied by micro-Electroluminescence measurements. It was found that this recombination was very local, which has lateral size less than 1 µm and spectral peak position around 600 nm. Changes of growth conditions led to a reduction in the concentration of these defects, improving the current-voltage characteristics and slightly enhancing the optical efficiency of green LEDs.1 Introduction GaN-based light emitting diodes (LEDs) operating in the range of green-to-violet are commercially available and have received much attention. The GaN-based LEDs were usually grown on sapphire substrates and had high density of different defects, especially dislocations. However, it was noted that the high external quantum efficiency was achieved for blue and violet LEDs. Generally, the optical efficiency of green LEDs is lower than that of blue LEDs. Moreover, the current voltage (I-V) characteristics, for example, the ideality factors for green LEDs are usually higher than those for blue LEDs especially at low current regime. Degradation in I-V characteristics was attributed to the tunneling process [1,2]. The spectra of tunneling emission in blue and green LEDs under low current regime were intensively investigated [2][3][4]. In our work, we used the confocal microscopy to study the distribution and spectral properties of local tunneling recombination emission (~600 nm) in green LEDs under low current regime.

Conduction Mechanisms of Leakage Currents in InGaN/GaN-Based Light-Emitting Diodes

“…Hence, it is necessary to deeply understand the role of defects in limiting the performance of LED devices. Recently, there have been reports that the undesirable local dot-like emissions are due to highdensity TDs under both reverse and forward biases [7], [8]. There have also been attempts to find the transport mechanism of the undesirable leakage current caused by the high-density TDs [5].…”

Optical emission characteristics of semipolar (1\,1\,\bar{2}\,2) GaN light-emitting diodes grown on m-sapphire and stripe-etchedr-sapphire

“…Non-uniformity in the InGaN-MQWs was not seen in the photoluminescence spectra of MQWs grown on these templates, exhibiting single-peak emission (not shown here). Bias-dependent sub-bandgap emission in LEDs are either attributed to band filling of tail states [29], or tunneling-assisted radiative recombination [24][25][26]. In particular, band-to-band tunneling-assisted recombination has been shown to occur in blue c-plane LEDs, resulting in a green sub-threshold emission, potentially due to localized diffusion of Mg dopants [24].…”