CHEMICAL MICROANALYSIS OF SEMICONDUCTOR HETEROSTRUCTURES BY THICKNESSFRINGE IMAGING

Thickness fringes observed in [100] bright field images of 90-degrees wedge specimens of semiconductor heterostructures are sensitive to cry stal chemistry. Following extensive experience in the recording and in terpretation of such images for the purpose of chemical microanalysis, we report on the following topics: (i) a reliable procedure for prepa ring 90-degrees wedge specimens by cleaving; (ii) a theoretical analys is of fine structure associated with the thickness fringe profiles and an assessment of its chemical sensitivity; and (iii) analysis of expe rimental thickness fringe profiles, recorded from a set of AlxGa1-xAs structures whose composition had previously been determined by X-ray r ocking curve methods. By comparing calculated thickness profiles with experimental images recorded with a solid state slow scan CCD camera, it is estimated that the Al x-fraction can be measured to an accuracy of 0.02 over the composition range 0.3 < x < 0.6.