Chapter 8 Conclusions and Prospective
8.2 Prospective
In the next-generation optoelectronic devices, the nanometer-scale materials promise to be important due to numerous unique properties expected in the
low-dimensional system. Low-dimensional ZnO nanostructures, such as QDs, nanoparticles (NPs), nanobelts, nanowires, and quantum wells, have been widely
investigated for the feasible requirement. In particular, ZnO QDs and NPs are of great interest because of the three-dimensional confinement of carrier and phonon leads not
only continuous tuning of the optoelectronic properties but also improvement in device performance. Nevertheless, the surface of QDs is usually composed of uncoordinated
atoms, which make the QDs highly active and quench the PL emission. Since, the modification of surface of ZnO QDs becomes imperative issue for next generation of
optoelectronic devices.
In experiment, in order to combine the advantages of QDs and Mg-doped ZnO, ZnO-MgO core-shell structure is the most interesting topic for our works. That can overcome the effect of surface defects in ZnO, especially in QDs system which has large
surface-volume ratio. Because the band gap energy of MgO is much larger than that of ZnO, the ZnO-MgO core shell QDs should have better emission efficiency than ZnO
QDs.
We will suggest to also use simple sol-gel method to add Mg(OAc)2·4H2O in ZnO QDs solution then stir at 40°C. When the prepared new solution drops on Si then take to be annealed for 300°C to 700°C. The primary results of the low temperature PL spectra
of samples annealed at various temperatures that we observed a broaden emission from MgZnO alloy and two sharp emission from ZnO. We also found that the defect emission has been diminished from sample 300°C to 700°C. To further investigate more
characteristic of ZnO-MgO core-shell QDs, the temperature dependent PL and
time-resolved PL should proceed.
In other way, according to above experiment data, the effective-mass approximation
apparently gives a good understanding of the blue shift of the optical absorption threshold.
However, this approach fails for the smallest crystallite sizes because of the
oversimplified description of the crystal potential as a spherical well of infinite depth. A better description of the band structure can be obtained from a tight-binding (TB)
framework. Since the atomic structure is implicitly considered, this method is more adequate for small crystallites. In the future, I will calculate the electronic structure and
optical properties of ZnO QDs using TB approximation. Once the tight-binding parameters are known, we can calculate the eigenvalues of Hamiltonian H. This matrix
is formed by 4×4 block matrices describing the interactions on the same atom (intra-atomic) or between two first-nearest neighbors (interatomic). If N is the number
of atoms in the crystallite, the dimension of H is 4N and a direct diagonalization becomes impossible for several hundred atoms. To circumvent this problem we will use the
recursion method or symmetry basis method. Such large matrices can be diagonalized with the help of group theory; partial diagonalization is effected by using the projection
operators of the point group to form-basis states. Thus, computation time is reduced based on symmetry-TB method.
林國峰簡歷 (Vita)
基本資料
姓名: 林 國 峰 (Kuo-Feng Lin) 性別: 男
出生年月日: 1977 年 10 月 18 日 籍貫: 花蓮縣
永久通訊處: 花蓮縣豐濱鄉大港口村 9 鄰 50 號 Email: xia117.eo92g@nctu.edu.tw
xia117.eo94g@nctu.edu.tw 學歷:
2001.9 - 2003.6 國立台北科技大學光電科技系 學士 2003.9 – 2005.6 國立交通大學光電工程研究所 碩士 2005.9 – 2008.10 國立交通大學光電工程研究所 博士 博士論文題目:
實驗及理論探討奈米結構之氧化鋅光學性質研究
Experimental and theoretical study on the influence of finite crystallize optical properties in ZnO
nanostructures
Publication list
I. Refereed Journal Publications:
1. Kuo-Feng Lin, Hsin-Ming Cheng, Hsu-Cheng Hsu, Li-Jiaun Lin, Wen-Feng Hsieh, “Band gap variation of size-controlled ZnO quantum dots synthesized by sol–gel method,” Chemical Physics Letters 409, 208 (2005).
2. Hsin-Ming Cheng, Kuo-Feng Lin, Hsu-Cheng Hsu, Chih-Jen Lin, Li-Jiaun Lin, and Wen-Feng Hsieh, “Enhanced Resonant Raman Scattering and Electron-Phonon Coupling from Self-Assembled Secondary ZnO Nanoparticles,”
Journal of Physical Chemistry B 109, 18385 (2005).
3. Kuo-Feng Lin, Hsin-Ming Cheng, Hsu-Cheng Hsu, and Wen-Feng Hsieh,
“Band gap engineering and spatial confinement of optical phonon in ZnO quantum dots,” Appl. Phys. Lett. 88, 263117 (2006).
4. Hsin-Ming Cheng, Kuo-Feng Lin, Hsu-Cheng Hsu, and Wen-Feng Hsieh, “Size dependence of photoluminescence and resonant Raman scattering from ZnO quantum dots,” Appl. Phys. Lett. 88, 261909 (2006).
5. Ching-Ju Pan, Kuo-Feng Lin, Wei-Tse Hsu and Wen-Feng Hsieh, “Raman study on alloy potential fluctuations in MgxZn1-xO nanopowders,” J. Phys.:
Condens. Matter 19, 186201 (2007).
6. Ching-Ju Pan, Kuo-Feng Lin and Wen-Feng Hsieh, “Acoustic and optical phonon assisted formation of biexcitons,” Appl. Phys. Lett. 91, 111907 (2007).
7. Ching-Ju Pan, Kuo-Feng Lin, Wei-Tse Hsu and Wen-Feng Hsieh, “Reducing exciton-LO phonon coupling with increasing Mg incorporation in MgZnO powders,” J. Appl. Phys. 102, 123504 (2007).
8. Wei-Tse Hsu, Kuo-Feng Lin, and Wen-Feng Hsieh, “Reducing exciton-longitudinal-optical phonon interaction with shrinking ZnO quantum dots ,“Appl. Phys. Lett. 91, 181913 (2007).
9. S. C. Ray, Y. Low, H. M. Tsai, C. W. Pao, J. W. Chiou, S. C. Yang, F. Z. Chien and W. F. Pong, K. F. Lin, H. M. Cheng and W. F. Hsieh, “Size dependence of the electronic structures and electron-phonon coupling in ZnO quantum dots,”
Appl. Phys. Lett. 91, 262101 (2007).
10. Kuo-Feng Lin, Ching-Ju Pan, and Wen-Feng Hsieh, “Calculations of electronic structure and density of states in the wurtzite structure of Zn1-xMgxO alloys using sp3 semi-empirical tight-binding model,” Appl. Phys. A. (2008).
11. Kuo-Feng Lin and Wen-Feng Hsieh, “Electronic band structures and surface states of ZnO finite well structures,” J. Phys. D: Appl. Phys. 41, 215307 (2008).
II. Conference:
1.
Kuo-Feng Lin, Hsu-Cheng Hsu, Hsin-Ming Cheng, and Wen-Feng Hsieh,“Influence of crystal size on the photoluminescence of ZnO quantum dots grown by sol-gel technique,” 2004 OPT 光電年會.
2.
Ming-Rung Tsai, Kuo-Feng Lin ,Hsu-Cheng Hsu, Hsin-Ming Cheng (andWen-Feng Hsieh, “以溶膠凝膠法製備MgxZn1-xO粉末之發光特性研究,” 2004 OPT 光電年會.
3.
Yi-Ching Lin, Kuo-Feng Lin, Chun-Yi Wu, Song Yang, Hsu-Cheng Hsu, and Wen-Feng Hsieh, “Nanowire-based dye-sensitized solar cell with ZNO nanowires manufactured by thermal vapor deposition,” 2005 OPT 光電年會.4.
W. F. Hsieh, H. M. Cheng, K. F. Lin, and H. C. Hsu, “Size Dependence of Band Gap Variation and Electron-phonon Coupling in ZnO Quantum Dots,＂ IQEC/CLEO-PR, Tokyo, Japan, 2005/11/07.5.
Wen-Feng Hsieh, Kuo-Feng Lin, Hsin-Ming Cheng, and Hsu-Cheng Hsu,“Spatial confinement of optical phonon in ZnO quantum dots,” Materials Research Society 2006 Spring Meeting, San Francisco, Ca., USA.