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InGaN light emitting diodes with a laser-treated tapered GaN structure

Wan-Chun Huang, Chia-Feng Lin, Tsung-Han Hsieh, Sin-Han Chen, Ming-Shiou Lin, Kuei-Ting Chen, Chun-Min Lin, Sy-Hann Chen, and Pin Han

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Abstract

InGaN light-emitting diode (LED) structures get an air-void structure and a tapered GaN structure at the GaN/sapphire interface through a laser decomposition process and a lateral wet etching process. The light output power of the treated LED structure had a 70% enhancement compared to a conventional LED structure at 20 mA. The intensities and peak wavelengths of the micro-photoluminescence spectra were varied periodically by aligning to the air-void (461.8nm) and the tapered GaN (459.5nm) structures. The slightly peak wavelength blueshift phenomenon of the EL and the PL spectra were caused by a partial compressed strain release at the GaN/sapphire interface when forming the tapered GaN structure. The relative internal quantum efficiency of the treated LED structure (70.3%) was slightly increased compared with a conventional LED (67.8%) caused by the reduction of the piezoelectric field in the InGaN active layer.

©2011 Optical Society of America

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Figures (6)
Fig. 1
Fig. 1 The schematic diagrams and fabricated procedures of the TP-LED structure with a tapered-GaN structure at GaN/sapphire interface were shown here.

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Fig. 3
Fig. 3 Microscopy images of the ST-LED and the TP-LED structures (a) with front-side light illumination (b) with back-side light illumination were observed. The light-intensity profiles of (c) the ST-LED structure (d) the TP-LED structure at a 20mA operation current are measured by a beam profiler.

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Fig. 2
Fig. 2 (a) The cross-sectional SEM micrographs of the laser scanning region and the lateral wet etching region at GaN buffer layer with a 40μm period width. (b) The cross-sectional SEM micrograph of the air-void structure at the laser scanning region through the N-face crystallographic wet etching process.

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Fig. 4
Fig. 4 (a) The EL spectra of the both LED structures were measured at 20 mA. (b) The current-voltage (I-V) characteristics and the light-output power as a function of the operating current are measured.

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Fig. 5
Fig. 5 The peak wavelength and the FWHM of the EL spectra were measured by varying the injection current. The peak wavelength and the FWHM of the EL spectra were measured at 464.3nm/21.6nm and 464.1nm/21.6nm for the ST-LED and the TP-LED, respectively, at a 20mA operation current. The thermal heat of the EL spectra were observed in the TP-LED structure with the peak wavelength red-shifted and line-width broadened phenomena.

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Fig. 6
Fig. 6 The PL spectra of (a) the TP-LED and (b) the ST-LED structures are measured at 10K and 300K. (c) The integral PL intensities of both LED structures are measured by varying the measurement temperatures. (d) The line-scanning PL emission intensity profile, scanning from non-treated region to treated region shown in the inserted OM image, is measured by the μ-PL measurement, and the periodic peak intensities and wavelengths of the μ-PL spectra are observed in the TP-LED structure.

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