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. 2017 Aug 29;7(1):9663.
doi: 10.1038/s41598-017-10086-7.

Electrically driven, highly efficient three-dimensional GaN-based light emitting diodes fabricated by self-aligned twofold epitaxial lateral overgrowth

Yang-Seok Yoo  1 , Hyun Gyu Song  1 , Min-Ho Jang  1 , Sang-Won Lee  1 , Yong-Hoon Cho  2
Affiliations

Electrically driven, highly efficient three-dimensional GaN-based light emitting diodes fabricated by self-aligned twofold epitaxial lateral overgrowth

Yang-Seok Yoo et al. Sci Rep. .

Abstract

Improvements in the overall efficiency and significant reduction in the efficiency droop are observed in three-dimensional (3D) GaN truncated pyramid structures fabricated with air void and a SiO2 layer. This 3D structure was fabricated using a self-aligned twofold epitaxial lateral overgrowth technique, which improved both the internal quantum efficiency and the light extraction efficiency. In addition, a reduced leakage current was observed due to the effective suppression of threading dislocations. While this study focuses primarily on the blue emission wavelength region, this approach can also be applied to overcome the efficiency degradation problem in the ultraviolet, green, and red emission regions.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Schematics of the GaN pillar structure fabrication, and investigations of different growth modes for A-LED and AS-LED based on growth times. (a–h) Top-view SEM images for A-LED and AS-LED at different growth times (t = 0, 500, 1000, 2500 s). The SiO2 layer is observed at the top region of AS-LED (e). An HSQ layer was added to avoid the regrowth of n-GaN and MQWs between GaN pillar structures. Although the n-GaN layer in A-LED is completely regrown on the surface of the GaN pillar structure, the n-GaN regrowth in the AS-LED is only observed around the tapered GaN pillar structure except for the c-plane area (b,f). The coalescent region in the AS-LED was observed in the dotted circle region, unlike the A-LED (c,g). By increasing the growth time even further, we observed nearly identical flat c-plane surfaces in both samples (d,f).
Figure 2
Figure 2
Differences in material quality between the samples: (a–c) panchromatic CL images, and (d–g) TEM images for P-LED, A-LED, and AS-LED. The hexagonal white dotted lines in the CL images indicate 3D structures.
Figure 3
Figure 3
TEM measurements of the effective active volume: (a) Top-view SEM image and (b) TEM images of QWs in semi-polar and polar facets for the A-LED and AS-LED. The hexagonal red dotted line in (a) indicates the unit cell area.
Figure 4
Figure 4
FDTD simulation results for light extraction of different sample structures: (a) Side view of the simulated sample structure for the A-LED and AS-LED. (b) Upper side light extraction efficiency for various simulated structures; λ det. was set at 400–550 nm, based on the EL data of the sample.
Figure 5
Figure 5
Comparison between efficiency and electrical characteristics: (a) Schematic layer structure of A-LED and AS-LED. (b) Light emission images at the same injection current (5 mA), (c) L-I curves, and (d,e) EQE and normalized EQE for P-LED, A-LED, and AS-LED.
See this image and copyright information in PMC

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