CHARACTERIZATION OF III-V SEMICONDUCTOR INTERFACES BY Z-CONTRAST IMAGING, EELS AND CBED

The application of scanning transmission electron microscopy (STEM)-ba sed techniques, atomic number (Z)-contrast imaging, electron energy-lo ss spectroscopy (EELS) and convergent beam electron diffraction (CBED) allows determination of chemical compositions at internal interfaces of semiconductor heterostructures as well as determination of local cr ystalline properties such as strain, relaxation effects or ordering wi th high lateral spatial resolution. Z-contrast images recorded at inte rnal heterostructure interfaces exhibit atomic spatial resolution in c ombination with qualitative chemical information. EELS can be used to record the chemical composition quantitatively but with slightly decre ased spatial resolution compared to Z-contrast imaging. However, EELS results can be used to calibrate the Z-contrast. Thus, the combination of both techniques can give quantitative information on the chemical composition at interfaces from monolayer to monolayer. The interpretat ion of Z-contrast imaging is further supported by Z-contrast simulatio ns. Examples demonstrating the performance of Z-contrast imaging (and simulation) and EELS are given for technically relevant Ill-V heterost ructure interfaces. Additionally, we used CBED in order to investigate the crystalline properties of cross sectional specimens from ternary and quaternary heterostructures of GaxIn1-xAsyP1-y on InP or GaAs subs trates. Even when using subnanometer electron probes, the quality of t he obtained CBED patterns is sufficient to perform local strain measur ements with 1 nm spatial resolution and with a sensitivity of (Delta a /a)(perpendicular to) approximate to 10(-3). This is proved by a CBED linescan across an alternately strained quaternary superlattice. CBED patterns recorded at interfaces directly exhibit symmetry violations, which are not yet understood satisfactorily. Therefore, further simula tions are necessary for a detailed quantitative understanding of CBED patterns from internal interfaces. The combination of Z-contrast imagi ng, EELS and CBED allows the extensive quantitative characterization o f semiconductor heterostructures and interfaces with the necessary lat eral spatial resolution down to the monolayer range. STEM-based techni ques are therefore an important tool for heterostructure and device de velopment.