Browsing by Author "Liu, Chuan-Cheng"

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Improvement of optical transmittance and electrical properties for the Si quantum dot-embedded ZnO thin film
(2013-10-23)
Kuo, Kuang-Yang
;
Liu, Chuan-Cheng
;
Huang, Pin-Ruei
;
Hsu, Shu-Wei
;
Chuang, Wen-Ling
A Si quantum dot (QD)-embedded ZnO thin film is successfully fabricated on a p-type Si substrate using a ZnO/Si multilayer structure. Its optical transmittance is largely improved when increasing the annealing temperature, owing to the phase transformation from amorphous to nanocrystalline Si QDs embedded in the ZnO matrix. The sample annealed at 700A degrees C exhibits not only high optical transmittance in the long-wavelength range but also better electrical properties including low resistivity, small turn-on voltage, and high rectification ratio. By using ZnO as the QDs' matrix, the carrier transport is dominated by the multistep tunneling mechanism, the same as in a n-ZnO/p-Si heterojunction diode, which clearly differs from that using the traditional matrix materials. Hence, the carriers transport mainly in the ZnO matrix, not through the Si QDs. The unusual transport mechanism using ZnO as matrix promises the great potential for optoelectronic devices integrating Si QDs.
Optical properties and sub-bandgap formation of nano-crystalline Si quantum dots embedded ZnO thin film
(2012-05-07)
Kuo, Kuang-Yang
;
Hsu, Shu-Wei
;
Huang, Pin-Ruei
;
Chuang, Wen-Ling
;
Liu, Chuan-Cheng
In this study, we fabricate ZnO thin films with nano-crystalline Si (nc-Si) quantum dots (QDs) using a ZnO/Si multilayer deposition structure and a post-annealing process, and the formation of high crystallinity of Si QDs embedded in the crystalline ZnO matrix is demonstrated. For optical properties, the essential features of ZnO material, high transmission in long-wavelength and high absorption in short-wavelength ranges, are preserved. We observe significantly enhanced light absorption and an unusual photoluminescence emission peak contributed from the nc-Si QDs in the middle-wavelength range. In addition, we confirm the formation of optical sub-bandgap and the obtained value is quite close to the unusual PL emission peak. We show that meaningful sub-bandgap can form in ZnO thin film by embedding nc-Si QDs while maintaining the advantageous properties of ZnO matrix. This newly developed composite material, nc-Si QD embedded ZnO thin films, can be useful for various electro-optical applications. (C)2012 Optical Society of America