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A19.2.1

Silicon Nanostructured Films Formed by Pulsed-Laser Deposition in Inert Gas and Reactive Gas X. Y. Chen, Y. F. Lu, Y. H. Wu, B. J. Cho, H. Hu Laser Microprocessing Laboratory and Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260

ABSTRACT We reported Si nanostructured films formed by pulsed-laser deposition (PLD) in both inert Ar gas and reactive O2 gas. The as-deposited nanostructured films with visible photoluminescence (PL) show a transition from a film structure to a porous cauliflowerlike structure, as the ambient gas pressure increases from 1 mTorr to 1 Torr. The film consists of small crystals with size from 1 to 20 nm. The oxygen composition of SiOx increases with increasing O2 gas pressure, while Si 2p peak of the Si dioxide also becomes dominate. At 100 mTorr O2 gas, almost complete SiO2 structure is formed. The PL at 1.8–2.1 eV is attributed to the quantum confinement effect (QCE) in Si nanocrystal core, while the PL band at 2.55 eV can be explained by the light emission from the localized surface states at SiOx/Si interface. Laser annealing was applied to the as-deposited nanostructured films. The PL intensities are increased by about two to three times of magnitude after annealing. High laser fluence causes damages in the films and optimal laser fluence exists before film damages or laser ablation occur.

INTRODUCTION The observation of photoluminescence (PL) in Si nanostructures [1-3] has attracted great interest due to their potential applications in microelectronics for nanocrystal floating gate memory and in optoelectronics for light emitting devices. The area of Si nanocrystals is currently one of the most active frontiers in physics and chemistry. Si nanocrystals have been synthesized by several techniques. Fabricating size-, distribution- and surface- controlled Si nanocrystals with reproducibility is critical to their promising applications. Among the fabrication methods, pulsed-laser deposition (PLD) is one of the most flexible and promising techniques due to its ability of size distribution control and maintaining crystal purity in a cold-wall processing ambient [4]. In the PLD method, the size distribution of Si nanocrystals can be controlled by varying background gas species and pressure, laser fluence, target-tosubstrate distance, and subsequent annealing or oxidation. On the other hand, the properties and functions of the Si nanocrystals are greatly determined by surface condition and crystal structure. Annealing is necessary to achieve good crystallization. Laser annealing has been well developed to remove lattice damage and defects in crystals. Laser annealing can provide several advantages such as selected area processing, rapid crystallization without any change in intrinsic structure, and avoidance of surface contamination which plays a significant role in the strong visible luminescence from Si nanostructures. In this work, PLD was used to fabricate Si nanocrystals in