Nowadays semiconductor structures can be generated of low dimensions that charge carriers are confined to a space of only some nm3 and thus quantum-physical phenomena become important. The properties of so-called quantum structures essentially depend on the perfection of their structure, size, arrangement, morphology, and on their chemical composition.
The potential of combined use of conventional transmission electron microscopy (CTEM), high-resolution imaging (HRTEM) and digital image analysis is applied to study quantum dot (QD) structures in various semiconductor materials. The classical diffraction contrast method is applied to visualize the strain field in the surrounding of the QDs. Dark-field imaging allows a qualitative analysis of chemical composition using chemically sensitive reflections. Furthermore, it will be presented how the techniques of quantitative HRTEM (qHRTEM) can be used to determine the local strain, chemical composition and the structural peculiarities on atomic scale.
In detail, respective results gained from the following quantum structures will be presented:
(i) Ga(Sb,As) QDs grown by metalorganic chemical vapour deposition (MOCVD) on GaAs substrates,
(ii) (Si,Ge) islands grown by liquid phase epitaxy (LPE) on Si substrates
The possibilities and limitations of different program packages for the qHRTEM will be demonstrated.