The Constrained Growth and Patterned Distribution of nc-Si from a-SiN x /a-Si:H/a-SiN x : Mechanism and Experiments
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The Constrained Growth and Patterned Distribution of nc-Si from a-SiNx/a-Si:H/a-SiNx: Mechanism and Experiments K.J. Chen, K. Chen, L.C. Wu, Z.Y. Ma, P.G. Han, W Li, L Zhang, Y.J. Zhang, X.F. Huang National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, P. R. China ABSTRACT We get size-controlled nanocrystalline silicon (nc-Si) from a-SiNx/a-Si:H/a-SiNx sandwich structures by thermal annealing. Transmission electron microscope analyses show that the mean size and the grain size distribution (GSD) of the nc-Si are controlled by the annealing conditions and the a-Si sublayer thickness. We build a theoretical model of constrained crystallization which can well interpret the phenomena of the growth halt of nc-Si and higher crystallization temperature for the thinner a-Si sublayer. The experimental results indicate that constrained crystallization method is promising to achieve uniform and high density nc-Si array either by thermal annealing or by laser annealing. Based on this investigation we employ the method of laser interference crystallization (LIC) to fabricate nanocrystal Si with the two-dimensional (2D) patterned distribution within 10 nm thick a-Si:H single layer. Si nano-crystallites are selectively located in the discal regions within the initial a-Si:H layer. The present method is promising to fabricate various patterned nc-Si arrays for device applications simply by changing the geometry of the mask. INTRODUCTION Low-dimensional semiconductor systems, such as nanocrystalline silicon (nc-Si), are currently being studied for the purpose of new application in both nanoelectronic and photoelectronic devices[1-4]. The size and position control of uniform nc-Si grains is the key technology for the device application. We propose a model on constrained growth in a-SiNx/a-Si:H/a-SiNx sandwich structures to make uniform nc-Si grains and a method for getting patterned nc-Si distribution. The model of the constrained growth of nc-Si has been studied in accordance with the classical thermodynamic theory. From our model, we determine the critical a-Si sublayer thickness of 34nm for the constrained crystallization growth and interpret the increase of the crystallization temperature for the ultra thin a-Si sublayer. We employ the method of laser interference crystallization (LIC) by using the 2D phase-shifting grating mask (PSGM) to fabricate nc-Si with 2D patterned distribution. The results show that Si nano-crystallites are formed and selectively located in the discal regions within the initial a-Si:H layer, which are patterned with the same 2D periodicity of 2.0 µm as the PSGM. THE MODEL OF CONSTRAINED GROWTH In the process of nucleation and growth, nc-Si in the a-Si:H sublayer with a-SiNx:H interfaces in our model undergoes the shape change from sphere-like to disc-like which is
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