Method and apparatus for determining a material's characteristics by photoreflectance using improved computer control.

摘要

A method and apparatus for determining the characteristics of materials, particularly of semiconductors, semiconductor heterostructures and semiconductor interfaces by the use of photoreflectance, in which monochromatic light and modulated light beam reflected from the sample (62) 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 (70) and the a.c. signal is used with another input of the computer (70) which controls the light intensity of the monochromatic light impinging on the sample (62) to maintain the d.c. signal substantially constant. A stepping motor (53) is preferably utilized for varying the light intensity of the monochromatic light which is controlled by a computer (70) to re-establish rapidly a predetermined d.c. signal established during normalization procedures when the light intensity of the monochromatic light changes, especially during change of its wavelength. Additionally, the modulation frequency of the modulated beam and/or the wavelength of the monochromatic light can also be varied by the computer (70).