DETERMINATION OF THE OPTICAL of CdS蒸发法

Assuming small variation of n2, m can be calculated using the following equations:
THEORETICAL BACKGROUND
The determination of the optical parameters is carried out for a system constituted by an absorbing CdS thin film deposited on a transparent substrate of finite thickness (see Fig. 1) The experimental set up which allows us, to calculate the transmission coefficient, of the system shown in fig. 1, is derived including reflection and transmission in an absorbing thin film, with smooth and parallel faces, bound by two semiinfinite media. Multiple incoherent reflections in the interface substrate/air are also included. Normal incidence was assumed and that the substrate is thick enough (>0.2 mm) to prevent interference effects in it. The transmission of the CdS/substrate system can be calculated using the following equation [8].
B = st - ρ svU
where
2 2 C = 4n k - zy - ρ U 2 z - n y 4k sin φ - 2cos φ + n 3 y + z 4k 2 sin φ zy + 4n 3 k 2 2cosφ 3 2 3 2
ADVANCES IN MATERIALS SCIENCE & TECHNOLOGY Vol. 1 Nº 1 Art. 2 pp. 07-12, 1996 ISSN 1316-2012 D. L. pp 96-0071
Recibido: 14-11-96 Aceptado: 03-12-96 Publicado: 22-12-96 © 1996 CIPMAT
D = uv - ρtuU 2
2 n − n + k2 u = 1 2 2
v = (n 2 − n 3 ) 2 + k 2 2 s = (n1 + n 2 ) 2 + k 2 2 t = (n 2 + n 3 ) 2 + k 2 2 2 - n2 + k 2 y = n2 1 2 2 - n2 + k 2 z = n2 3 2
T=
A exp(α d) B exp(2 α d) + C exp(α d) + D
(1)
Fig.1 System of an absorbing CdS thin films, on a finitethickness transparent media.
2 A = 16n 3 (1- ρ )(n 2 2 + k 2 )U
DETERMINATION OF THE OPTICAL CONSTANTS OF POLICRYSTALLINE CdS THIN FILMS PREPARED BY EVAPORATION
J. TORRES*, J.I. CISNEROS** & G. GORDILLO*** <Jatorres@ciencias.ciencias.unal.edu.co> * Pontificia Universidad Javeriana-Bogotá **Instituto de Fisica Gleb Wataghin, UNICAMP, CP 6165, CEP. 13083-970, Cidade Universitaria. Campinas, Brasil. *** Universidad Nacional de Colombia-Bogotá
DETERMINACIÓN DE LAS CONSTANTES ÓPTICAS EN PELÍCULAS DELGADAS DE CdS PREPARADAS POR EVAPORACIÓN EN ALTO VACIO
RESUMEN
En este trabajo se calculan las constantes ópticas y los espesores de películas delgadas de CdS fabricadas por evaporación en alto vacio. El método de cálculo se basa en la parametrización del indice de refracción de las muestras, con el modelo del oscilador simple, propuesto por WempleDiDomenico (W-D). Se presentan los espectros de transmisión y los valores correspondientes del índice de refracción, el coeficiente de absorción y el espesor de las películas. Palabras Clave: Propiedades Ópticas, Espectroscopía Óptica, Películas Delgadas, compuestos inorganicos, Semiconductores, Sulfuro de Cadmio, Evaporación, Vacancias.
FICHA: TORRES, J.; J. I., CISNEROS & G. GORDILLO, 1996.ADV. MAT. SCI. & TECH. 1(1):07-12.
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J. TORRES, J.I. CISNEROS & G. GORDILLO
源自文库
INTRODUCTION
(Cd,Zn)S compounds are widely used as photoconductors and as window materials for CdTe and CuInSe2 based solar cells [1,2]. It is important, for the development of these devices, to obtain information about optical properties of the constituent materials to achieve a good design of them. Many methods for the determination of the optical parameters of thin films materials, had been described [3,4]; however, we had found that these methods are not suitable to determine some optical parameters of II-VI compounds such as (Zn, Cd)S and (S, Se)Cd, probably due to that this kind of materials present heterogeneity in the refractive index, aspect which is not taken into account in the methods above referenced. In this work we describe a method to determine the optical constants of CdS thin films prepared by evaporation of CdSpowder, using a deposition system described elsewhere [5]. The optical constants: refractive index n(λ), absorption coefficient α(λ) and thickness d, were determined from transmittance measurements, carried out with a PerkinElemer lambda 9 spectrophotometer and using the model of the single effective oscillator proposed by Wemple and DiDomenico [6]
(
)
(
)
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DETERMINATION OF THE OPTICAL CONSTANTS OF POLICRYSTALLINE CdS THIN FILMS PREPARED BY EVAPORATION
In the case of a transparent substrate with refractive index n3 and considering multiple incoherent reflections at the substrate interfaces, the following expression for r is obtained.
(2)
φ = 4πn2d / λ
Where n2 is the film refractive index, k2 the extinction coefficient, d the film thickness and α the absorption coefficient and ρ is the transmittance correction factor associated to the weak absorption of the substrate.
ABSTRACT
The optical constants and thicknesses of CdS thin films were determined from transmittance measurements, using a simple method based on a parametrization of the refractive index by WempleDiDomenico (W-D) single oscillator model. The transmission spectra of typical thin films deposited by evaporation and their corresponding values of refractive index, absorption coefficient and thickness, are presented. Key Words: Optical properties, Optical Spectroscopy, Inorganic Compounds, Semiconductors, Sulphides, Cadmium Sulphide, Evaporation, Vacancies.