Lock-in amplifier-based rotating-analyzer spectroscopic ellipsometer with micro-controlled angular frequency
J.M. Flores-Camacho*, O.F. Núñez-Olvera, G. Rodríguez-Pedroza, A. Lastras Martínez, and L.F. Lastras-Martínez**
Instituto de Investigación en Comunicación Óptica, Universidad Autónoma de San Luis Potosí, Álvaro Obregón 64, 78000 San Luis Potosí, S.L.P., México.
* CONACyT fellow.
** Corresponding author: Phone: +52-444-825-0183; fax: +52444-825-01-98; e-mail: lflm@cactus.iico.uaslp.mx
]]>Recibido el 6 de octubre de 2004.
Aceptado el 22 de febrero de 2005.
Abstract
We report on the development of a full operational rotating analyzer spectroscopic ellipsometer. This instrument employs a phase-sensitive amplifier to process the optical signal as an alternative to Fast Fourier Transform analysis. We describe electronic hardware designed to stabilize the rotation frequency of the analyzer prism as well as to drive the device for the positioning of the polarizer prism azimuth. The ellipsometer allows for dielectric function measurement in the energy range from 1.7-5.5 eV, in both ambient air and Ultra High Vacuum (UHV). UHV measurements can be carried out at a temperature as low as 150 K. To evaluate the ellipsometer performance we present results of the determination of the complex dielectric function of a number of semiconductors, namely, GaSb, GaAs, InGaAs, CdTe and CdHgTe.
Keywords: Ellipsometers; control systems; dielectric function; optical properties of thin films.
Resumen
Se describen el diseño, la construcción y la operación de un elipsómetro espectroscópico de analizador rotante. El instrumento hace uso de un amplificador sensible a la fase para procesar la señal óptica; esto como una alternativa al análisis de la misma por la técnica de Trasformada Rápida de Fourier. Cuenta con dispositivos electrónicos diseñados para controlar la frecuencia de rotación del prisma analizador, así como para posicionar el ángulo azimutal del prisma polarizador. El elipsómetro permite la medición de la función dieléctrica en el rango de energías desde 1.7 eV hasta 5.5 eV, tanto en aire como en condiciones de Ultra Alto Vacío (UHV). En UHV es posible realizar mediciones a temperaturas tan bajas como 150 K. Para evaluar la operación del elipsómetro, se presentan resultados de la medición de la función dieléctrica de un número de semiconductores, en forma específica, de GaSb, GaAs, InGaAs, CdTe y CdHgTe.
]]> Descriptores: Elipsómetros; sistemas de control; función dieléctrica; propiedades ópticas de películas delgadas.
PACS: 07.60.Fs, 07,05.Dz; 78.20.-e; 78.66.-w
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Acknowledgments
The authors would like to thank to Dr. R.E. Balderas-Navarro for helpful discussions, M.C.J. Nieto-Navarro, E. Ontiveros and J. Ramirez for their expert technical support and R.A. Flores for the drawing of Fig. 3. This work was partially supported by CONACyT through grant No. 41248-F.
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