Thin film composition determination by means of integrated intensity measurements

Abstract

A new method based on measurement of the absorption of an x-ray beam diffracted from a substrate has been used to determine the film composition in an InGaAs/InP nearly-lattice-matched single heterostructure.The absorption coefficient, μInGaAs, of the InGaAs alloy was obtained by accurately measuring the InGaAs layer thickness and the integrated intensities of several diffractions of the InP substrate compared with the integrated intensities of the equivalent peaks of an InP reference crystal. By using the tabulated Ga, As and In absorption factors, the In content was then determined. It is shown that in the case of an InGaAs alloy the accuracy in In content determination can reach 1%. The absolute In content of the InGaAs epilayer was found to be 4%–5% larger than expected from the linear dependence of the lattice parameter on the alloy composition as stated by the Vegard law.This result has been confirmed by a diffraction profile auto-fitting software; with the assumption of the Vegard law the best fit of the 004 diffraction profile of the InGaAs/InP heterostructure could only be obtained with a 4.6% larger InGaAs thickness, to compensate for the larger In content as determined by the absorption measurement.