Simulation of Layer Thickness Measurements of Quantum Well Structures by in Situ Single-Wavelength Ellipsometry

Simulations have been performed of the polarizer (P) and analyzer (A) readings that would result from in situ ellipsometric measurements at 632.8 nm of specific quantum well structures using a Faraday-modulated null ellipsometer. It is shown that for a GaAs-A1GaAs quantum well structure involving layers that differ by 2 % in the real part of their index of refraction at 632.8 nm the variation in P and A is small, i.e., 1.5 ~ in P and 1 ~ in A. However, it is shown that the Faraday-modulated null ellipsometer with an accuracy of better than 0.01 ~ in P and A can make meaningful measurements on such quantum well structures. The simulations show that the layer thicknesses can be measured to an accuracy of 0.1 nm in 10.0 nm and that it is easy to discriminate between layers that differ by 0.01 in the real part of the index of refraction or 2.5 % in the imaginary part of the index of refraction. The simulations show that it is possible to follow the growth of superlattices. The possibility of using such a Faraday-modulated null ellipsometer to control the deposition of quantum well layers is discussed. Quantum well structures 1 consist of thin single-crystal layers of different semiconductors deposited epitaxially on a single-crystal semiconductor substrate. The semicon-ducting layers forming quantum well structures have bee