DETERMINATION OF INTERFACE COMPOSITION IN III-V HETEROJUNCTION DEVICES (HT AND RTD) WITH ATOMIC-RESOLUTION USING STEM TECHNIQUES

In this work, we will present the determination of chemical compositio n across heterointerfaces in the layer stacks of devices such as heter ojunction bipolar transistors (HBT) and resonant tunneling diodes (RTD ) by scanning transmission electron microscopy (STEM). We used STEM-ba sed atomic number (Z) contrast imaging in order to analyze interface a bruptness in HBT and RTD structures qualitatively with monolayer spati al resolution. Electron energy-loss spectroscopy (EELS) was used for t he quantitative chemical analysis of individual ultrathin layers such as RTD barriers. The obtained structural data can be used to improve a nd refine device modeling and design, e.g., composition profiles can b e converted into band structures or barrier widths and exact barrier s hapes in RTDs can be measured directly. Examples for correlations betw een structural data and device properties will be given for InP-based HBT and RTD structures. (C) 1997 Published by Elsevier Science S.A.