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InGaN-based light-emitting diodes with an embedded conical air-voids structure

Yu-Chieh Huang, Chia-Feng Lin, Sy-Hann Chen, Jing-Jie Dai, Guei-Miao Wang, Kun-Pin Huang, Kuei-Ting Chen, and Yi-Hsiang Hsu

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Abstract

The conical air-void structure of an InGaN light-emitting diode (LEDs) was formed at the GaN/sapphire interface to increase the light extraction efficiency. The fabrication process of the conical air-void structure consisted of a dry process and a crystallographic wet etching process on an undoped GaN layer, followed by a re-growth process for the InGaN LED structure. A higher light output power (1.54 times) and a small divergent angle (120°) were observed, at a 20mA operation current, on the treated LED structure when compared to a standard LED without the conical air-void structure. In this electroluminescence spectrum, the emission intensity and the peak wavelength varied periodically by corresponding to the conical air-void patterns that were measured through a 100nm-optical-aperture fiber probe. The conical air-void structure reduced the compressed strain at the GaN/sapphire interface by inducing the wavelength blueshift phenomenon and the higher internal quantum efficiency of the photoluminescence spectra for the treated LED structure.

©2010 Optical Society of America

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Figures (4)
Fig. 1
Fig. 1 The fabricated procedures of the conical air-void structure at GaN/sapphire interface are shown.

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Fig. 2
Fig. 2 (a)(b) The SEM micrographs of the truncated conical-hole pattern are observed. (c)(d) After the re-growth process, the conical air-void structures are observed at the GaN/sapphire interface. (e)(f) The light-intensity profiles of the CAV-LED structures were measured at 20 mA. The higher light intensity region is observed as the circular patterns distributed on the whole LED chip.

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Fig. 3
Fig. 3 (a) The light output power and the operation voltage are measured by varying the injection current. (b) The light emission intensity of both LED structures are measured by varying the detected angles from 0° (normal direction) to 180° (backside direction). (c) Far-field radiation patterns of both LED structures were measured at 20 mA.

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Fig. 4
Fig. 4 (a) Peak wavelengths of the EL spectra were measured by varying the operating current. (b) The line-scanning EL emission intensity profile is measured by an optical fiber probe, and the periodical peak intensity and wavelength of the EL spectra are then observed. The PL spectra of the (c) ST-LED and (d) the CAV-LED structures are measured at 10K and 300K to calculate the internal quantum efficiencies.

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