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

Abstract

This paper reviews the formation of nanoscale V-shaped pits on GaN-based light emitting diodes (LEDs) grown by the metal organic chemical vapor deposition (MOCVD) system and studies the effect of V-shaped pits on quantum efficiency. Since V-pits could provide potential barriers around threading dislocations to lessen non-radiative recombinations in such a high defect environment. In our study, multiple InGaN/GaN quantum well samples with different emission wavelengths of 380, 420, 460, and 500 nm were grown, each with different nanoscale V-shaped pits of three diameters for 150, 200, and 250 nm, respectively. It was found that the multiple quantum well (MQW) sample with larger V-pits had a lower pit density, but a relatively larger total V-pits defected area. The optimum diameter of V-pits showing the highest quantum efficiency from the MQW sample depended on the emission wavelength. MQW samples with wavelengths of 380 and 500 nm exhibited the best internal quantum efficiency (IQE) performance at the smallest V-pits area; however, the best performance for MQW samples with wavelength around 420 and 460 nm occurred when large V-pit areas were presented. Photoluminescence (PL) peak shifts and Raman shifts can provide a relationship between quantum-confined Stark effect (QCSE) and IQE, as well as a comparison between strain and IQE. The results obtained in this phenomenological study shall provide a useful guide line in making high-performance GaN-based LEDs with wide emission spectra.

Enhanced Efficiency InGaN/GaN Multiple Quantum Well Structures via Strain Engineering and Ultrathin Subwells Formed by V-Pit Sidewalls

“…Figure d shows that their size and density increase with the number of SL layers (values are shown in Table ). These findings are supported by extant research, indicating that the V-pit density and size are also dependent on the growth conditions, indium composition, and MQW thickness, as well as the InGaN/GaN SL growth temperature and the location at which the V-pit formation commences. ,, For example, V-pits that emerged in the first SL layer have greater size compared to those that are formed in the middle or the top of SLs . According to our STEM observations, in all samples, V-pit generation is induced by the conditions at which the n -GaN layer is grown below the SLs.…”

“…5,23,25 For example, V-pits that emerged in the first SL layer have greater size compared to those that are formed in the middle or the top of SLs. 26 According to our STEM observations, in all samples, V-pit generation is induced by the conditions at which the n-GaN layer is grown below the SLs. Therefore, large V-pit sizes (exceeding 270 nm in diameter, as shown in Table 1) were observed, while sidewalls were formed along the [11̅ 01] direction comprising SLs and MQWs, resulting in much greater thickness, compared to that previously reported, 22,23 whereby thickness increased with the number of SLs incorporated into the structure.…”

Investigation of Emission Heterogeneity in InGaN/GaN Micro-Light-Emitting Diodes by Photon-Correlation Cathodoluminescence Spectroscopy

“…Since there is no correlation between wavelength shift and lifetime, there must be a mechanism that affects the EQE and the spectra, but not the IQE. It has been observed by Chen et al 29 that V-pits can alter the emission properties of LEDs during operation, with wavelength decreasing as total V-pit surface increases. V-pits cause strain relaxation, 30 which could cause a blue-shift in the surrounding QW emission, similarly to the edge.…”

A Review on Experimental Measurements for Understanding Efficiency Droop in InGaN-Based Light-Emitting Diodes

“…Thus, in our fitting, we have to assume a uniform carrier distribution to calculate the carrier concentration. In a commercial LED, by using the V-pit technique [ 93 ], the hole injection uniformity at different QWs can be improved effectively through lateral injection from the sidewalls of V-pit. Thus, the QW number is usually around 10 or even up to 15.…”