Transformation of optical properties of Si-rich Al 2 O 3 films at thermal annealing
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Transformation of optical properties of Si-rich Al2O3 films at thermal annealing E. Vergara Hernandez1, B. Perez Miltan1, J. Jedrzejewski2 and I.Balberg2 1
UPIITA-Instituto Politecnico Nacional, Mexico DF, 07320, Mexico
2
Racah Institute of Physics, Hebrew University, 91904 Jerusalem, Israel
ABSTRACT The effect of thermal annealing on the optical properties of Al2O3 films with different Si content was investigated by the photoluminescence method. Si-rich Al2O3 films were prepared by RF magnetron co-sputtering of the silicon and alumina targets on long quarts glass substrates. Photoluminescence (PL) spectra of freshly prepared Si-rich Al2O3 films are characterized by three PL bands with the peak positions at 2.97-3.00, 2.25-2.29 and 1.50 eV. The thermal annealing of the films at 1150 oC during 30 min stimulates the formation of Si nanocrystals (NCs) in the film area with Si content exceeded 60%. After the thermal annealing the PL intensity of all mentioned PL bands decreases and the new PL band appears with the peak position at 1.67 eV. The new PL band is attributed to the photo currier recombination inside of Si NCs. The size of NCs estimated from the PL peak position 1.67 eV of Si NC emission is about ~-4.5-5.0 nm. The temperature dependences of PL spectra of Si-rich Al2O3 films have been studied in the range of 10-300K with the aim to reveal the mechanism of recombination transitions for mentioned above PL bands 2.97-3.00, 2.25-2.29 and 1.50 eV in freshly prepared films. The thermal activation of PL intensity and permanent PL peak positions in the temperature range 10300K permit to assign these PL bands to defect related emission in Al2O3 matrix. INTRODUCTION Light emitting Si nanocrystalls (NCs) were studied intensively during the last 20 years due to their attractive aspects for electronics and photonics related to the possibility to joint in a single chip the Si base devices for the realization of short scale optic interconnections [1-3]. Other promising application of Si NCs is in biology owing to the low toxicity of Si in comparison with II –VI semiconductor quantum dots widely used for the image production [4,5]. Si NCs in dielectric matrix are interesting as well for the charge trapped nonvolatile memory devices [6]. The different types of matrices (SiO2, ZrO2, HfO2, Al2O3) have been studied for the application of Si NCs in nonvolatile memory devices [7,8]. In the following, the luminescence properties of Si-rich Al2O3 films obtained by RF magnetron spattering will be presented. EXPERIMENTAL DETAILS Si-rich Al2O3 films were deposited by radio frequency (RF) magnetron co-sputtering from two targets (Si and Al2O3) in argon plasma on a long glass substrate a 10-mm width and a 140-mm length as it is shown in figure 1. Five groups of samples, entitled as it is shown in figure 1 (2A, 4A, 6A, 8A, 10A), with the different contents of Si were chosen for the investigation. The freshly prepared Si-rich Al2O3 films were then annealed at 1150oC during 30 min in ambient air to form the Si NCs inside of the Al2O3 matr
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