Reflectance anisotropy spectrometer for real time crystal growth investigations

A new reflectance anisotropy (RA) spectrometer is presented. The numerous similarities with phase modulated ellipsometry (PME) are emphasized. The RA spectrometer takes advantage of the high frequency modulation (50 kHz) provided by a photoelastic modulator. Moreover as compared to other techniques, this RA spectrometer allows the determination of both the real and the imaginary part of the RA signal. The use of optical fibers in both optical arms allows an increase of the compactness of the spectrometer. The adaptation of RA to a MOCVD reactor is described in detail. Four detectors can be used simultaneously providing the real-time spectroscopic capability. The numerical data system of the detected signal is based on the use of a high precision analog-digital converter and a fast Fourier transform processor. Moreover, on-line relations between the data acquisition system and external analog signals and triggers are available. Thus it can be inferred that this reflectance anisotropy spectrometer appears a useful tool for high sensitivity optical measurements and in situ control processing.