Chee Yong Fong, Sha Shiong Ng, NurFahana Mohd Amin, Fong Kwong Yam and Zainuriah Hassan
This study aims to explore the applicability of the sol-gel-derived GaN thin films for UV photodetection.
Abstract
Purpose
This study aims to explore the applicability of the sol-gel-derived GaN thin films for UV photodetection.
Design/methodology/approach
GaN-based ultraviolet (UV) photodetector with Pt Schottky contacts was fabricated and its applicability was investigated. The current-voltage (I-V) characteristics of the GaN-based UV photodetector under the dark current and photocurrent were measured.
Findings
The ideality factors of GaN-based UV photodetector under dark current and photocurrent were 6.93 and 5.62, respectively. While the Schottky barrier heights (SBH) for GaN-based UV photodetector under dark current and photocurrent were 0.35 eV and 0.34 eV, respectively. The contrast ratio and responsivity of this UV photodetector measured at 5 V were found to be 1.36 and 1.68 μA/W, respectively. The photoresponse as a function of time was measured by switching the UV light on and off continuously at different forward biases of 1, 3 and 6 V. The results showed that the fabricated UV photodetector has reasonable stability and repeatability.
Originality/value
This work demonstrated that GaN-based UV photodetector can be fabricated by using the GaN thin film grown by low-cost and simple sol-gel spin coating method.
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Hui Yuen Peng and Fong Kwong Yam
In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and…
Abstract
Purpose
In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and spectral characteristic of white LED are dependent on the temperature, causing thermal effects on luminous efficacy and color shift of white LED become a critical application checkpoint to be addressed by white LED manufactures. Thus, the purpose of this paper is to minimize the thermal stability issue affecting white LED luminescence during operation by introducing phosphor sedimentation process.
Design/methodology/approach
The LED samples were assembled and sent for centrifugation with 0, 5 and 10 revolutions per second (rps), respectively, during phosphor sedimentation process. Luminescence properties of these LED samples were then characterized at a varying temperature to investigate the effect of phosphor sedimentation on the luminescence stability of LED samples. The LED samples were also cross-sectioned and analyzed to understand the phosphor sedimentation mechanism. Computational fluid dynamics (CFD) was applied to study the temperature distribution of the non-phosphor sediment (NPS) and phosphor sediment (PS) LED during operation to validate the hypotheses based on experimental data.
Findings
Experimental results show that the luminous intensity of PS LED samples degrades less significant at high temperature. The experimental results also show that the color coordinate for PS LED samples is more stable and is less blue-shifted than NPS LED samples as the temperature increased. These are because the heat generated by phosphor particles during operation can be dissipated effectively throughout a high thermal conductivity substrate after phosphor sedimentation. Thus, the phosphor temperature of PS LED is lower than NPS LED during operation as validated with the thermal simulation.
Practical implications
The study of this paper is applicable as a reference for industries who intend to resolve the thermal stability of white LED during operation. The luminescence properties changes as a function of the temperature study in this paper can be used to predict the application performances of white LED accurately. Apart from that, the analysis method of temperature distribution using CFD simulations can be extended by other CFD users in the future.
Originality/value
Implementation of phosphor sedimentation to reduce thermal instability issue of white LED has yet to be reported on previous studies. Most literature just studied the thermal instability issue of either assembled LED or raw material, without suggesting any solution to tackle the issue.
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This paper aims at illustrating how the local and the decentralized temple management bodies were made governable and governed through law.
Abstract
Purpose
This paper aims at illustrating how the local and the decentralized temple management bodies were made governable and governed through law.
Design/methodology/approach
This paper examines the implementation of Chinese Temples Ordinances (the Ordinance) and the activities of the Chinese Temples Committee (the Committee) in Hong Kong during colonial times by analyzing official archival records from 1920s to 1970s.
Findings
This paper delineates how the local and decentralized temple management bodies were made governable under the Ordinance. The Ordinance and the Committee translated Chinese temples into financial resources for Chinese charity activities managed by the elite merchant class. Chinese temples were also sometimes translated as obstacles for land development. Though there existed different representations of Chinese temples in practices, the Committee and related officials provided legal reasons under the same legal framework suggested by the Ordinance.
Originality/value
This paper suggests that folk religion as a research topic is not only relevant to studies of religious doctrine, belief and ritual performances. A study of the history of temple management bodies is also highly relevant to the study of colonial governance in Hong Kong. It adds value to the discussion on the trajectory of the development of local communities.