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In-situ single-wavelength fast-nulling ellipsometric measurements on CdTe-Cd1-xMnxTe quantum well and superlattice structures grown by pulsed-laser evaporation and epitaxy

An EXACTA 2000 Faraday-modulated fast-nulling ellipsometer operating at 6328 angstrom has been used in situ to measure the polarizer (P) and analyzer (A) angles produced by CdTe-Cd1-xMnxTe quantum well and superlattice structures during growth by pulsed laser evaporation and epitaxy. This ellipsometer is capable of measuring P and A with a relative accuracy of 0.003 degree(s) at a rate of 10 points per second. This makes it especially useful in monitoring the growth of quantum wells and superlattice structures. From fitting the ellipsometric data, the thicknesses of the layers in CdTe-Cd1-xMnxTe quantum well and superlattice structures can be determined with an accuracy of 5% for layers more than 100 angstrom thick and with an accuracy of 10% for layers less than 100 angstrom thick. However, when each layer of thickness less than 100 angstrom in a CdTe-Cd1-xMnxTe superlattice consists of two sublayers with different indices of refraction, then the accuracy of the thickness determination is only 20%. The possibility of using such a Faraday-modulated fast-nulling ellipsometer to control the deposition of quantum well layers and superlattices is discussed.