Optical and Electrical Properties of Ti<SUB>x</SUB>Si<SUB>1-x</SUB>O<SUB>y</SUB> Films

Abstract

Manuscript received May 19, 2009; revised Sept. 29, 2009; accepted Oct. 9, 2009 I. IntroductionTiO 2 has attracted attention due to its high dielectric constant (κ) and high refractive index (n). However, TiO 2 has disadvantages of a high leakage current and a low crystallization temperature below 400°C [1]. One way of overcoming these problems is fabricating a mixture of TiO 2 and a low κ material, such as SiO 2 and Al 2 O 3 [2]. It is expected that a mixed material like Ti x Si 1-x O y (TSO) film will show improved leakage current and breakdown voltage. If the compositions of the mixture are controlled accurately, the dielectric constant and refractive index can be tailored, which will be useful in fabricating optical and electronic devices. Plasma-enhanced atomic layer deposition (PEALD) is a powerful method to deposit thin films with precise controls of the mixed material composition and film thickness [2], [3]. Tailoring the refractive index and film thickness provides many advantages, particularly in the fabrication of antireflection (AR) coating films used as solar cells. In the field of thin film solar cells, AR coating with the designed optical thickness (a product of refractive index and film thickness) is required to enhance solar cell efficiency [4], [5]. High κ materials such as TiO 2 and ZnO have been used as AR coated films in Si thin film solar cells [6]-[8]. However, ZnO shows a photo induced variation of electrical properties under visible illumination [9].Multilayer AR coating with refractive index variation effectively enhances the solar cell efficiency [10], [11]. Precise control of the optical thickness of TSO films grown using PEALD will be useful for the light-capturing structure of thin film solar cells.To secure a wide refractive index range, a low n material (such as SiO 2 and Al 2 O 3 ) and a high n material (such as TiO 2 ) should be selected to fabricate an AR coating for a thin film solar cell. In this study, 4 ], respectively. The formation of one cycle for SiO 2 is TEOS/source purge (SP)/O 2 gas (plasma)/reactant gas purge (RP), and that for TiO 2 is TTIP/SP/O 2 gas (plasma)/RP. The plasma power density was about 0.4 W/cm 2 , and the plasma was turned on only during the supply of O 2 reactant gas. The purging gas was Ar, and the reactant gases were O 2 +Ar. The formation of one cycle for the TSO film is N Ti subcycles of TiO 2 , and N Si subcycles of SiO 2 , which designates the cycle coordinates (N Ti , N Si ).For example, TSO (1, 2) designates one cycle of TiO 2 and two cycles of SiO 2 [13]. TSOs of (1, 2), (1, 1), (2, 1), and (3, 1) were fabricated; thus, the Ti content varied with the cycle coordinates. To obtain reflection spectra curves, TSO films were deposited on a p-type Si (100) wafer as shown in Fig. 1(a), and for I-V measurement, a metal/TSO/ITO/glass structure was fabricated as shown in Fig. 1(b). The I-V measurement was performed with a voltage mode, which means that voltages were supplied and then currents were measured. In addition, the I-V curves were measured ...

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“…Metal oxide nanoparticles may potentially be inexpensive alternatives to carbon nanotubes with superior properties for many applications including catalysis, separation, gas storage, energy conversion, drug release, sensing and environmental protection, and biocompatible nanocomposites. The modified form of TiO 2 composites such as TiO 2 -SiO 2 , TiO 2 /SiO 2 are interest for their potential application, such as electrolytes in dye-sensitized solar cells, anti reflection coating, photocatalysts and so on [1][2][3][4][5][6][7].…”