Determination of interface composition in III-V heterojunction devices (HBT and RTD) with atomic resolution using STEM techniques

In this work, we will present the determination of chemical composition across heterointerfaces in the layer stacks of devices such as heterojunction bipolar transistors (HBT) and resonant tunneling diodes (RTD) by scanning transmission electron microscopy (STEM). We used STEM-based atomic number (Z) contrast imaging in order to analyze interface abruptness in HBT and RTD structures qualitatively with monolayer spatial resolution. Electron energy-loss spectroscopy (EELS) was used for the quantitative chemical analysis of individual ultrathin layers such as RTD barriers. The obtained structural data can be used to improve and refine device modeling and design, e.g., composition profiles can be converted into band structures or barrier widths and exact barrier shapes in RTDs can be measured directly. Examples for correlations between structural data and device properties will be given for InP-based HBT and RTD structures.