Investigation of silicon nanoclusters embedded in ZnO matrices deposited by cosputtering system
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Chih-Hong Liu Institute of Electro-Optical Science and Engineering, National Cheng Kung University, 701 Tainan, Taiwan, Republic of China
Ching-Ting Leea) and Li-Ren Lou Institute of Microelectronics, Department of Electrical Engineering and Center for Micro/Nano Science and Technology, National Cheng Kung University, 701 Tainan, Taiwan, Republic of China
Wen-Yung Yeh and Mu-Tao Chu Optoelectronics Semiconductor and System Application Div., Industrial Technology Research Institute, 310 Hsin Chu, Taiwan, Republic of China (Received 26 April 2008; accepted 11 June 2008)
A co-sputtering system was used to deposit silicon nanoclusters embedded in zinc oxide matrix (Si:ZnO) at low temperature without post-annealing. By adjusting the radio frequency power of the Si target during co-sputtering, Si:ZnO films with various crystallographic structures can be obtained. Silicon nanoclusters embedded in the zinc oxide matrix were examined using a high-resolution transmission electron microscope, x-ray diffractometer, and Fourier transformation infrared spectrometry. By comparing with photoluminescence spectra, we can clearly identify quantum confinement effect of silicon nanoclusters embedded in the ZnO matrix.
I. INTRODUCTION
II. EXPERIMENTAL PROCEDURE
Recently, low-dimensional silicon-based nanocluster materials and the resulted light-emitting devices have been studied intensively. Highly efficient optoelectronic devices based on silicon-based nanoclusters embedded in silicon oxide and silicon nitride matrices have also been demonstrated.1–3 However, the applications of those matrices are seriously limited due to the highly resistive nature of these materials. Thus, it is important to control resistivity of these silicon-based nanocluster materials. It is also possible to embed silicon-based nanoclusters in zinc oxide (ZnO). With high hardness and amenability to conventional chemical wet etching, ZnO has become a promising candidate for various device applications.4–8 In this work, a radio-frequency (rf, 13.56 MHZ) magnetron cosputtering system was used to deposit silicon nanoclusters embedded in ZnO films on either Si or sapphire substrates at low temperature without postannealing. Physical and electrical properties of the deposited samples will also be discussed.
Thin films of Si nanoclusters embedded in ZnO matrix (Si:ZnO) were deposited on either Si(100) or sapphire substrates using a rf magnetron co-sputtering system. In this study, 99.999% pure Si and 99.99% pure ZnO were used as the target materials. To obtain various Si contents on the Si:ZnO thin films, the rf power of the Si target was varied from 0 W to 125 W while that of ZnO target was fixed at 75 W. During co-sputtering, both Si and ZnO targets were inclined with respect to the normal direction of the substrates. Therefore, the Si and ZnO could be deposited on the substrates simultaneously. The substrate holder was neither cooled nor heated externally. However, it was rotated to improve the uniformity in thickness and the Si content of the deposited film.
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