Structural and Optical Properties of Al2O3 with Si and Ge Nanocrystals
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0958-L07-06
Structural and Optical Properties of Al2O3 with Si and Ge Nanocrystals Selcuk Yerci1, Ilker Yildiz1,2, Ayse Seyhan1, Mustafa Kulakci1, Ugur Serincan1,3, Michael Shandalov4, Yuval Golan4, and Rasit Turan1 1 Department of Physics, Middle East Technical University, Ankara, 06531, Turkey 2 Central Laboratory, Middle East Technical University, Ankara, 06531, Turkey 3 Department of Physics, Anadolu University, Eskisehir, 26470, Turkey 4 Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
ABSTRACT Si and Ge nanocrystals were formed in Al2O3 matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si0 signals corresponding to Si nanoclusters increase while Si4+ signals related to a-SiO2 disappear from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive stress exerted on the formed nanocrystals were also studied by Raman spectroscopy. Photoluminescence spectra of the Al2O3 containing nanocrystals were discussed by means of Ti and Cr impurities, as well as F centers. The existence of the amorphous Ge nanoclusters in Al2O3 matrix significantly enhances the light emission of Ti3+ impurities. INTRODUCTION Bulk Si and Ge with their indirect band gaps are poor light emitters for optoelectronic applications. However, increasing demand for high speed data processing and communication necessitates development of integrated optical systems which is possible only with light emission from these materials. In 1990, a strong room temperature photoluminescence (PL) was observed from porous Si [1]. After this observation, Si and Ge nanostructures became a very active field of research to realize the light emission from these elements [2]. Although prototypes of Light Emitting Diodes (LED) based on Si nanocrystals (Si-nc) were produced [3], the origin of the luminescence is still controversial. Several studies aimed to clarify the emission mechanism of the light generated in SiO2 containing Si nanocrystals [4]. On the other hand, it has been recently shown that the nature of the oxide matrix surrounding nanocrystals has a significant influence on the optical emission from these structures [5]. In order to improve light emission, alternative production methods have also been suggested [6]. Si and Ge nanocrystals embedded in an oxide matrix have also been used for the fabrication of a new generation of non-volatile memory devices [7]. Nanocrystal based memory devices are considered as the replacement of the traditional floating gate devices essentially due to better reliability and lower power consumption. Moreover, shrinking dimensions of gate dielectrics requires alternative materials with dielectric constants higher than that of SiO2. Al2O3 with its relatively higher dielectric constant can be a potential candidate for the replace
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