The TEM thickness fringe method [1] was developed as a potential routine technique to determine compositional profiles in quantum well systems. This technique has the advantages that a) TEM sample preparation is simple and the experiment is easy to set up and b) thickness fringe profiles show fine structure which is sensitive to chemistry [2]. In this paper, we demonstrate the ability of the method to measure the chemical abruptness at the interface between two layers of different composition.

90° wedge AlGaAs/GaAs TEM samples were prepared by the cleavage method, where the samples were cleaved along two orthogonal {110} planes. The samples were mounted on Cu grids and were investigated in a Philips EM430 TEM. Samples were orientated to the [100] direction precisely and bright-field images were acquired digitally using a CCD camera. Fig 1 shows an enlarged image of thickness fringes.

Since the edges of samples are 90° wedges, the thickness at any point can be accurately determined and the fringe profile can be compared with fringe profiles calculated for a range of Al compositions.