Browsing by Author "Chang, S. J."

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GaN p-i-n photodetectors with an LT-GaN interlayer
(2008-04-01)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Huang, K. C.
Nitride-based p-i-n ultraviolet (UV) photodetectors with a low-temperature (LT) GaN interlayer were proposed and fabricated. Compared with a conventional GaN p-i-n photodetector, it was found that both the dark current and ideality factor of the p-i-n photodetector with an LT-GaN interlayer became larger whereas the UV-to-visible rejection ratio became smaller because of the poor crystal quality of the LT-GaN interlayer. However, the responsivity of the GaN p-i-n photocletector with an LT-GaN interlayer was larger than that of the conventional GaN p-i-n photocletector under a high reverse bias because of the carrier multiplication effect and/or internal gain that originated from the defect levels.
GaN-based light-emitting diodes prepared on vicinal sapphire substrates
(2007-02-01)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Huang, K. C.
Thin InGaN epitaxial layers and GaN-based light-emitting diodes (LEDs) on conventional and vicinal cut sapphire substrates are prepared. It is found that indium atoms are distributed much more uniformly in the samples prepared on vicinal cut sapphire substrates. It is also found that stronger electroluminescence intensity can be achieved without the band-filling effect of localised states from the LEDs with vicinal cut sapphire substrate. With 20 mA current injection, it is found that 44% electroluminescence intensity enhancement can be achieved by using the 1 degrees tilted sapphire substrate.
GaN-Based Light-Emitting-Diode With a p-InGaN Layer
(2014-03-01)
Chen, P. H.
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Kuo, Cheng-Huang
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Lai, W. C.
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Chen, Yu An
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Chang, L. C.
GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick p-In0.01Ga0.99N layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.
High responsivity of GaN p-i-n photodiode by using low-temperature interlayer
(2007-10-22)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Huang, K. C.
Gallium nitride p-i-n ultraviolet photodiodes with low- temperature (LT)- GaN interlayer have been fabricated. It was found that the dark current of photodiode with LT- GaN interlayer is as small as 143 pA at 5 V reverse bias. It was also found that the responsivity of the photodiode with LT- GaN interlayer can be enhanced at a small electric field (similar to 0.4 MV/cm) due to the carrier multiplication effect. The UV photocurrent gain of 13 and large ionization coefficient (alpha = 3.1 X 10(5) cm(-1)) were also observed in the detector with LT- GaN interlayer. Furthermore, we can achieve a large peak responsivity of 2.27 A/W from the photodiode with LT- GaN interlayer. (C) 2007 American Institute of Physics.
Improved external quantum efficiency of GaN p-i-n photodiodes with a TiO2 roughened surface
(2008-01-01)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Huang, K. C.
Gallium nitride p-i-n ultraviolet photodiodes (PDs) with a titanium dioxide (TiO2) nano-particles roughened surface have been fabricated. It was found that the responsivity and external quantum efficiency can be improved 60% on the surface roughened PDs. It was also found that light absorption can be enhanced from various incident angles by the TiO2 roughened surface. Furthermore, the high detectivity of 9.2 x 10(1.3) cm.Hz(1/2).W-1 can be achieved from the PD with a rough surface.
Liquid crystal alignment on the a-C : H films by Ar plasma ion immersion
(2007-07-31)
Chang, S. J.
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Wu, K. Y.
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Yang, Y. H.
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Hwang, J.
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Wu, Hsin-Ying
A plasma ion immersion treatment has been developed to enhance the liquid crystal (LC) alignment on the hydrogenated amorphous carbon (a-C:H) layer in an inductively coupled plasma (ICP) chamber. No LC alignment was observed for the a-C:H layer tilted at an angle of 0 degrees during the bombardment with plasma ions. The LC alignment occurs for the a-C:H layer tilted at an angle of 30 degrees or 60 degrees. Their pretilt angles (similar to 1.4 degrees) are approximately the same. The azimuthal anchoring strength is 1.98 x 10(-6) J/m(2) at a tilted angle of 30 degrees and 1.14 x 10(-4) J/m(2) at a tilted angle of 60 degrees. The mechanism for the LC alignment is attributed to the oblique incidence of ions within the matrix sheath of non-uniform thickness near the a-C: H surface under a negative pulse bias. The matrix sheath of non-uniform thickness is confirmed by the plasma density distribution in the ICP chamber and the X-ray photoemission spectra across the a-C:H layer. (C) 2007 Elsevier B.V. All rights reserved.
Low dark current GaN p-i-n photodetectors with a low-temperature AIN interlayer
(2008-07-01)
Lin, J. C.
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Su, Y. K.
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Chang, S. J.
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Lan, W. H.
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Chen, W. R.
GaN p-i-n ultraviolet (UV) photodetectors (PDs) with a low-temperature (LT)-AIN interlayer were proposed and fabricated. It was found that the dark current of such detectors is as small as 28pA even at a high reverse bias of 40 V. Although the high potential barrier at the AIN-GaN interface would slightly reduce the responsivity of PD under low reverse biases, the high UV-to-visible rejection ratio of the PD with an LT-AIN interlayer could be achieved under high reverse biases due to its very low dark current. The rejection ratio of the PD with the LT-AIN interlayer is as large as 735 at the reverse bias of 40 V.
Single Crystalline GaN Epitaxial Layer Prepared on Nano-Patterned Si(001) Substrate
(2011)
Huang, C. C.
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Chang, S. J.
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Kuo, C. H.
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Wu, C. H.
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Ko, C. H.
The authors report the growth of GaN epitaxial layers on nano-patterned Si(001) substrates prepared by the standard facilities used in integrated circuit (IC) industry. It was found that we could achieve high-quality single crystalline GaN by using the 50 nm SiO(2) recess patterned Si(001) substrate. It was also found that we can reduce the tensile stress in GaN epitaxial layer by about 95% using the nano-patterned Si(001) substrate, as compared to the conventional un-patterned Si(111) substrate. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3569753] All rights reserved.
Tunable complex magnetic states of epitaxial core-shell metal oxide nanocrystals fabricated by the phase decomposition method
(2016-07-13)
Chang, S. J.
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Lam, T. N.
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Yang, C. Y.
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Chen, Y. L.
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Chu, Y. H.
We report on the successful fabrication of epitaxial-discrete CoxFe3-xO4/CoO magnetic nanostructures on a SrTiO3 substrate as well as the results of a thorough investigation of the magnetic cross-reactions of the two phases in the vicinity of the epitaxial junction. These nanostructures were originally prepared as Fe3O4-CoO core-shell structures through the phase decomposition of bismuth perovskite precursors by pulsed-laser deposition. An antiphase boundary emerged during the structural/electronic transition from the CoO core to the Co1-xFe2+XO4 shell; this then developed into a ferrimagnetic/antiferromagnetic interface. Uncompensated spins (UCS) arose from the CoxFe3-xO4/CoO interface as a result of strong ferrimagnetic-antiferromagnetic interactions. A notable exchange bias as well as a significant exchange enhancement was observed owing to the UCS, which had a locking effect because of the decoupling of the Co1-xFe2+XO4/CoO reversal from the antiphase boundary. Control of the precursor ratio allowed for the fine-tuning of the Co1-xFe2+XO4 phase and the associated locking behaviors. This, in turn, allowed the anisotropy and coercivity of the nanostructures to be manipulated. Thus, we were able to create and thoroughly understand a complex epitaxial configuration with tunable structural and magnetic properties. This study should open new opportunities with regard to current magnetic oxide technology, which requires novel methods for pursuing extremity of controllable properties over an atomic landscape.