Effects of N 2 O Fluence on the PECVD-grown Si-rich SiO x with Buried Si Nanocrystals
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A19.11.1
Effects of N2O Fluence on the PECVD-grown Si-rich SiOx with Buried Si Nanocrystals Chun-Jung Lin1, Hao-Chung Kuo1, Chia-Yang Chen1, Yu-Lun Chueh2, Li-Jen Chou2, Chih-Wei Chang3, Eric Wei-Guang Diau3, and Gong-Ru Lin1* 1 Department of Photonics and Institute of Electro-Optical Engineering National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, Taiwan 300, R.O.C. 2 Department of Materials Science and Engineering National Tsing Hua University, 101, Section 2 Kuang Fu Road, Hsinchu, Taiwan 300, R. O. C. 3 Department of Applied Chemistry and Center for Interdisciplinary Molecular Science National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, Taiwan 300, R.O.C. *Corresponding author ABSTRACT The optimized N2O fluence is demonstrated for plasma enhanced chemical vapor deposition (PECVD) of Si-rich substoichiometric silicon oxide (SiOx) films with buried Si nanocrystals. Strong room-temperature photoluminescence (PL) at 550-870 nm has been observed in SiOx films grown by PECVD under a constant SiH4 fluence of 20 sccm with an N2O fluence varying from 105 sccm to 130 sccm. A 22-nm-redshift in the central PL wavelength has been detected after annealing from 15 min to 180 min. The maximum PL irradiance is observed from the SiOx film grown at the optimal N2O fluence of 120 sccm after annealing for 30 minutes. Larger N2O fluence or longer annealing time leads to a PL band that is blue-shifted by 65 nm and 20 nm, respectively. Such a blue shift is attributed to shrinkage in the size of the Si nanocrystals with the participation of oxygen atoms from N2O incorporated within the SiOx matrix. The (220)-oriented Si nanocrystals exhibit radii ranging from 4.4 nm to 5.0 nm as determined by transmission electron microscopy (TEM). The luminescent lifetime lengthens to 52 µs as the nc-Si size increase to > 4 nm. Optimal annealing times for SiOx films prepared at different N2O fluences are also reported. A longer annealing process results in a stronger oxidation effect in SiOx films prepared at higher N2O fluences, yielding a lower PL irradiance at shorter wavelengths. In contrast, larger Si nanocrystals can be precipitated when the N2O fluence becomes lower; however, such a SiOx film usually exhibits weaker PL at longer wavelength due to a lower nc-Si density. These results indicate that a N2O/SiH4 fluence ratio of 6:1 is the optimized PECVD growth condition for the Si-rich SiO2 wherein dense Si nanocrystals are obtained after annealing. INTRODUCTION Quantum-confinement in nc-Si leads to an increase in the band gap energy and in the spatial overlap of the electron and hole wave functions in the Si. These effects increase the spontaneous emission rate and shift the emission peak to higher energies than that of bulk Si [1, 2]. It has been demonstrated that Si nanocrystal (nc-Si) related photoluminescence (PL) can be enhanced with increasing annealing temperature and time. The red shift of the peak PL wavelength with increasing annealing temperature was attributed to the nc-Si of larger diameters. has been explained by qua
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