Browsing by Author "Yang, Hung-Chih"

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Influence of LT-GaN nucleation layer on the structural and optical properties of MOVPE-grown a-plane GaN
(2010-04-01)
Chang, Shih-Pang
;
Yang, Hung-Chih
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
The influence of the LT-GaN nucleation layer on the quality of the GaN template was investigated by the study of the surface morphology of the nucleation layer, and of the crystalline and optical properties of the subsequently grown a-plane GaN template. Both X-ray diffraction and photoluminescence results reveal that better crystalline and optical quality could be obtained using thinner nucleation layer thickness and higher V/III ratio, leading to brighter near band edge luminescence as compared to films grown on lower V/III ratio nucleation layer. Our experiments indicate that reduction in the density of nucleation layer islands can effectively improve the crystalline quality of a-plane GaN template, and the V/III ratio of nucleation layer is a more dominant growth parameter to improve the crystalline and optical quality at the same time. The optimized growth parameters for the nucleation layer in our study are thickness of 10 nm and V/III ratio of 9000. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Light Output Enhancement of GaN-Based Light-Emitting Diodes by Optimizing SiO2 Nanorod-Array Depth Patterned Sapphire Substrate
(2012-04-01)
Chiu, Ching-Hsueh
;
Tu, Po-Min
;
Chang, Shih-Pang
;
Lin, Chien-Chung
;
Jang, Chung-Ying
In this study, we investigated high-efficiency InGaN/GaN light-emitting diodes (LEDs) grown on sapphire substrates with SiO2 nanorod arrays (NRAs) of different heights. The GaN film showed an improved crystal quality through X-ray diffraction (XRD) full-width at half-maximum (FWHM), photoluminescence (PL), and cathodoluminescence (CL) measurements. The light output power and internal quantum efficiency (IQE) of the fabricated LEDs were increased when compared with those of conventional LEDs. Transmission electron microscopy (TEM) images suggested that the voids between SiO2 nanorods and the stacking faults introduced during the nanoscale epitaxial lateral overgrowth (NELOG) of GaN can effectively reduce the threading dislocation density (TDD). We believe that the improvements could be attributed to both the enhanced light extraction by utilizing SiO2 NRAs and the improved crystal quality through the NELOG method. We found that the sample with SiO2 NRA structures of 200 nm height can increase the LED output power by more than 70% in our study. (C) 2012 The Japan Society of Applied Physics
Low Droop Nonpolar GaN/InGaN Light Emitting Diode Grown on m-Plane GaN Substrate
(2010)
Chang, Shih-Pang
;
Lu, Tien-Chang
;
Zhuo, Li-Fu
;
Jang, Chung-Ying
;
Lin, Da-Wei
The low droop nonpolar m-plane InGaN/GaN light emitting diode (LED) has been fabricated and investigated. The external quantum efficiency for a 300x300 mu m square LED chip only drops about 18% from maximum at an operation current of 22 A/cm(2) (20 mA) to 330 A/cm(2) (300 mA) dc operations at room temperature. In addition, the internal quantum efficiency has been extracted by temperature-dependent photoluminescence measurements, and there is no droop observed as the carrier density increases. The small droop in efficiency of m-plane LEDs could be due to the lack of polarization effects that enhances the carrier confinement under high current density operation. The polarization anisotropy is clearly observed in the m-plane LED, and the degree of polarization is 68%.