The measurement of the period and strain of semiconductor superlattice systems using HREM

Abstract

The quantification of local strains in semiconductor epilayer systems is of technological importance since strain can affect the physical, electrical and optical properties of the material. For the measurement of strains in epitaxial structures on the nanometer scale, high resolution electron microscopy (HREM) images recorded using slow scan charged-coupled device cameras and analyzed using Fourier filtering techniques can provide reliable, quantitative results that are independent of image contrast.Fig. 1a is a HREM image of about 3 periods from a 20 period In.82Al.18Sb / InSb coherently strained superlattice in [110] zone axis projection. The superlattice was grown by magnetron sputter epitaxy and the growth direction is along [001]. The image was recorded at 200 kV using a Philips CM20 TEM. Displayed is a 128×697 pixel subset of the original 256×1024 image. This image was Fourier transformed to obtain the digital diffractogram and all reflections apart from the [002] were filtered out using elliptical masks of approximately the first Brillouin zone in size. The inverse Fourier transform, displaying the [002] lattice fringes, is presented in Fig. 1b.