Photoluminescence and Photoluminescence Excitation Mechanisms for Porous Silicon and Silicon Oxynitride
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ABSTRACT Through a comparative study of the light emission and light excitation property of porous silicon (PS) and Si oxide, photoluminescence (PL) and photoluminescence excitation (PLE) mechanisms for blue-light-emitting PS are analyzed. Strong blue light (445nm) and ultraviolet light (365nm) emission from silicon-rich silicon oxynitride films at room temperature were observed. An analysis of the PL and PLE spectra of PS and Si oxide indicated that for blue-light emission from PS, there are two types of photoexcitation processes: photo-excitation occurring in nanometer Si particles (NSP's) and in the Si oxide layers covering NSPs, and radiative recombination of electron-hole pairs taking place in luminescence centers (LCs) located on the interfaces between NSP's and Si oxide and those inside Si oxide layers. The PL spectra of silicon-rich silicon oxynitride films implies that the PL originated from some LCs in SiO, and SiONy:H, while PLE spectra indicates that photoexcitation occurs in NSPs, SiOx and SiOxNy:H. The 365 nm band is attributed to the former two photoexcitation processes and the 445 nm one to the third process. As such, the quantum confinement/luminescence center model appears to be a satisfactory model in explaining the experimental results. INTRODUCTION Blue and ultraviolet light-emitting semiconductors are of great interest as it has promising applications in color displays and optoelectronic devices. The demonstration of visible photoluminescence (PL) in porous Si (PS) by Canham [1] spawned much of the current interest in this field. To date, a substantial amount of work has been done on the PL and electroluminescence (EL) on PS and silicon oxynitride films [2-9] since these materials are very promising in the integration of electrical and optical components. Several techniques for fabricating silicon oxynitride films have been developed, including nitridation of silicon powder [10], rapid thermal growth of silicon oxynitride films on Si in N 2 0 [ 11], and sputtering [12]. Peters et al [13] used CVD method with SiH 4 , N 2 and 02 as reaction gases to grow silicon oxynitride films. For depositing SiNx films, electron cyclotron resonance PECVD method with SiI-I 4 and N 2 as reaction gases were used [14-16]. Some researchers form silicon nitride islands by thermal nitridation of clean Si surface by N2 exposure [ 17-18]. They found that N 2 molecules are reactive enough for SiN nucleation and that nitrogen coverage increases almost linearly with increasing exposure time. Gallard et al [19] reported N 2 might react with SiH 4 to form SiOxNy. Inspired by these reports, we pursued rf PECVD technique with highly hydrogen diluted Sill4 , N 2 and 02 (N2 and 02 come
141 Mat. Res. Soc. Symp. Proc. Vol. 588 ©2000 Materials Research Society
from controlled leakage of reaction chamber) as reaction gases to deposit silicon-rich silicon oxynitride films. The study of PL and PLE mechanisms for porous silicon (PS), silicon oxynitride films as well as other light-emitting materials are extremely important. By ide
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