Browsing by Author "Chu, Chia-Hung"

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Defect induced ferromagnetic ordering in epitaxial Zn0.95Mn0.05O films on sapphire (0001)
(2019-12-04)
Liu, Wei-Rein
;
Pao, Chih-Wen
;
Yu, Doris Weijyun
;
Chin, Yi-Ying
;
Wu, Wen-Bin
We report the influence of Mn dopant on magnetic properties of Zn0.95Mn0.05O (ZMO)/Al2O3(0001) hetero-epitaxial systems grown by using pulsed-laser deposition. The room temperature (RT) intrinsic ferromagnetic (FM) ordering verified by superconducting quantum interference device magnetometer and x-ray magnetic circular dichroism spectrum of Mn L-2(,3) edges is ascribed to the substitutional Mn atoms in the Zn site of ZnO. Mn in ZMO has a tetrahedral local symmetry instead of the octahedral symmetry of MnO, after verifying the absence of the Mn-related impurities or clusters in ZMO epitaxial film by Mn K-edge and Zn K-edge x-ray absorption spectroscopy spectrum, as well as the analysis of long-range structural ordering on Renninger scan of forbidden (0005) reflection in x-ray diffraction, transmission electron microscopy and Raman spectrum. Comparison of x-ray absorption spectra of ZMO with those of ZnO epilayers at O K-, Zn K-, and L-3-edges indicates that the substitution of the Zn site with Mn enhances the charge-transfer (CT) transition and the presence of Zn vacancies (V-Zn) also dominate the photoluminescence (PL) spectrum, implying that the formation of numerous V-Zn defects plays an important role in activating FM interactions. The strong CT effect and the existence of high-density V-Zn suggest that the intrinsic RT FM ordering of insulating ZMO is a result of the formation of the bound magnetic polarons (BMPs) that interact with each other via intermediate magnetic impurities.
ORGANIC PHOTOSENSITIVE OPTOELECTRONIC DEVICE
(2010-11-11)
Meng, Hsin- Fei
;
Hong, Sheng-Fu
;
Tseng, Hsin-Rong
;
Chen, En-Chen
;
Chu, Chia-Hung
An organic photosensitive optoelectronic device includes an anode, an organic photosensitive layer formed on the anode and having a donor portion and an acceptor portion, a hole blocking layer formed on the organic photosensitive layer so as for the organic photosensitive layer to be sandwiched between the anode and the hole blocking layer, and a cathode formed on the hole blocking layer so as for the hole blocking layer to be sandwiched between the cathode and the organic photosensitive layer. The highest occupied molecular orbitals (HOMO) of the hole blocking layer is at least 0.3 eV higher than that of the donor portion. Therefore, the optoelectronic device efficiently suppresses dark current so as to enhance sensitivity when applied to a detector.