Optics: measuring and testing – By shade or color – With color transmitting filter
Patent
1989-07-20
1993-11-09
Willis, Davis L.
Optics: measuring and testing
By shade or color
With color transmitting filter
356432, G01N 2125
Patent
active
052607720
ABSTRACT:
A method and apparatus for determining the characteristics of materials, particularly of semi-conductors, semi-conductor heterostructures and semi-conductor interfaces by the use of photoreflectance, in which monochromatic light and modulated light beam reflected from the sample is detected to produce a d.c. signal and an a.c. signal, whereby the d.c. signal is applied to one input of a computer and the a.c. signal is used with another input of the computer which controls the light intensity of the monochromatic light impinging on the sample to maintain the d.c. signal substantially constant. A stepping motor is preferably utilized for varying the light intensity of the monochromatic light. Additionally, the modulation frequency of the modulated beam and/or the wavelength of the monochromatic light can also be varied by the computer. Growth conditions of semi-conductor materials as well as information about trap times can be obtained by analyzing the energy band gaps and determining the dependence of the in-phase photoreflectance signal on the pump modulating frequency, respectively.
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Shen et al. "New Normalization Procedure for Modulation Spectroscopy, " Rev. Sci. Instrum. vol. 58, #8, Aug. 1987 pp. 1429-1432.
Ginley et al, Photoelectrochemistry and Electrosynthesis on Semiconductor Materials, vol. 88-14, pp. 468-476.
Pollak Fred H.
Shen Hong-En
Craig, Jr. Paul M.
Hantis K. P.
Willis Davis L.
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