Nonlinear optical properties of plasma enhanced chemical vapour deposition grown silicon nanocrystals
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Nonlinear optical properties of plasma enhanced chemical vapour deposition grown silicon nanocrystals
G. Vijaya Prakash1, M. Cazzanelli1, Z. Gaburro1, L. Pavesi1, F. Iacona2 and F. Priolo3 1
INFM and Dipartimento di Fisica, Università di Trento, via Sommarive 14, 38050, Povo, Trento, Italy; 2CNR-IMETEM, Stradale Primosole 50, 95121 Catania, Italy, 3INFM and Dipartimento di Fisica, Università di Catania, Corso Italia 57, 95129 Catania, Italy ABSTRACT We present a systematic study on the nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma enhanced chemical vapour deposition (PECVD). The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ(3) of Si-nc are measured by Z-scan method. While the closed aperture Z-scan reveals a sign of positive nonlinearity, the open aperture measurements suggests a nonlinear absorption coefficients. Absolute values of χ(3) are in the order of 10-9 esu and show systematic correlation with the Si-nc size, due to quantum confinement related effects. INTRODUCTION Wide attention has been paid on research on silicon nanocrystals (Si-nc), after the first observation of visible emission from porous Si [1,2]. Besides the intense visible emission characteristic features of Si-nc, they are also promising materials for nonlinear optical applications. Numerous reports are available on the nonlinear optical properties of Si-nc by using porous Si [3], but a more systematic study of well-defined systems is required, particularly to elucidate the role of quantum confinement and interface states. Large variation in nonlinear optical coefficients is observed in earlier reports due to the differences in sample characteristics and to different fabrication methods [4,5]. In this paper we present a detailed report on the nonlinear optical properties of Si-nc grown by a very versatile technique, plasma-enhanced chemical vapour deposition (PECVD). The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibilities, χ(3) for different sized Si-nc are measured at 813 nm using z-scan technique in the femtosecond regime. A specific correlation is made between the nanocrystal size and χ(3) to study the quantum confinement related effects. EXPERIMENTAL PROCEDURE The SiOx films were prepared by using a parallel plate PECVD system. The films have a three layers waveguide geometry, where two 100 nm thick SiO2 films sandwiched a 230 nm thick SiOx layer, deposited on quartz substrate. An error of 10% can be estimated on the thickness of the films. High temperature annealing of SiOx films induces phase separation
K8.3.1 Downloaded from https://www.cambridge.org/core. Macquarie University, on 22 Jun 2020 at 16:42:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-722-K8.3
between Si and SiO2 and as a consequence, Si-nc are formed. The preparation method and experimental procedure are reported elsewere [6-8]. The z-scan experiments are performed on Si-
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