Structural and optical characterization of Si quantumdots in a SiC matrix
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1260-T11-03
Structural and optical characterization of Si quantumdots in a SiC matrix M. Kuenle1, P. Löper1, M. Rothfelder1, S. Janz1, K.-G. Nickel2, O. Eibl3 1
Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, D-79110 Freiburg, Germany 2
Eberhard-Karls-University, Tuebingen, Institute for Geoscience, Applied Mineralogy, Wilhelmstraße 56, 72074 Tuebingen, Germany 3
Eberhard-Karls-University, Tuebingen, Institute for Applied Physics, Auf der Morgenstelle 10, D-72076 Tuebingen, Germany
ABSTRACT Amorphous hydrogenated Si1-xCx / SiC multilayers consisting of alternating Si1-xCx and stoichiometric SiC layers were prepared using Plasma Enhanced Chemical Vapour Deposition (PECVD). Annealing at temperatures up to 1100°C was done targeting the size controlled crystallization of Si nanocrystals (NCs) in a SiC matrix. The influence of annealing temperature on the nanostructure of the multilayers was studied using Glancing Incidence X-ray Diffraction (GIXRD), Raman spectroscopy and Transmission Electron Microscopy (TEM). GIXRD reveal the crystallization of Si and SiC, when annealing temperatures exceed 900°C. The crystallization of Si and SiC was confirmed by TEM bright field imaging and electron diffraction. Annealing at 900°C, leads to the formation of Si NCs with a size of 3 nm, whereas the SiC NCs also have a size of 3 nm. However, a large amount of Si is still amorphous as shown by Raman spectroscopy. Annealing at temperatures exceeding 900°C reduces the amorphous phase and a further growth of Si NCs occurs.
INTRODUCTION For the fabrication of Si quantum dots in a dielectric matrix material commonly the superlattice approach introduced by Zacharias et al. is used [1]. During annealing, the growth of Si nanocrystals (NCs) is restricted by surrounding stoichiometric layers. The size and density of Si NCs can be controlled by the thickness and composition of the Si-rich layer. This has been successfully shown for Si NCs in SiO2 and Si3N4 matrices [2]. However, with decreasing thickness of the Si-rich layer the crystallization temperature of Si is strongly increasing [3]. First attempts to fabricate size controlled Si NCs in SiC were done by Song et al. [4, 5], using magnetron sputtered a-SiC:H / a-Si1-xCx:H multilayers. Annealing of the multilayers induced disruption of the layered structure and the formation of Si and SiC NCs.
EXPERIMENT The precursor gases silane (SiH4), methane (CH4), hydrogen (H) and argon (Ar) were used to deposit the a-SiC:H / a-Si1-xCx:H multilayers in a PECVD reactor (AK400) from the company Roth & Rau. As plasma source, a high frequency (13.56 MHz) was employed. The main deposition parameters were as follows: power density 0.1 W/cm2, deposition pressure 0.3 mbar and substrate temperature 250°C. Changes in chemical composition were achieved by the application of different SiH4 / CH4 ratios. Using this deposition parameters, a-Si1-xCx:H thin films having a C contend of up to 50 % are produced. Based on this process 20 bilayers consisting of (i) a-Si0.9C0.1:H layers with a thic
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