Structural nature of InAs NCQDs on GaAs(001)

Both the integration schemes noted above require deposition of the NCQDs on the semiconductor substrate. Therefore we would like to know the structural and chemical nature of the NCQDs in the as-deposited state. Given the NCQD size the only viable technique for their studies is high-resolution transmission electron microscopy (HRTEM). Most of the previous TEM studies of NCQDs have been performed when the NCQDs are deposited on amorphous substrates such as the image shown in fig. 2 in the introduction section. HRTEM studies on single crystal semiconductor substrate are not a simple matter. For imaging in plan-view geometry, the substrate thickness needs to be below ~ 20nm to be able to image contrast from NCQDs. Due to the fragility of the NCQDs, conventional techniques for semiconductor thinning based on ion-beam sputtering are not appropriate. We have therefore developed and applied new techniques for the specimen preparation based exclusively on chemical etching that are benign and enable maintaining the integrity of the integrated hybrid structures. A detailed account can be found in reference 1. Figure 1(a) and (b) show a low magnification TEM of an ensemble of InAs NCQDs on GaAs(001) and the corresponding electron diffraction pattern, respectively. The TEM image shows that the InAs NCQDs for dense close-packed patches. The ring pattern from the NCQD ensemble in fig. 1(b) reveals that the NCQDs are randomly oriented on the substrate.

Figure 1 (a) Plan-view TEM image of InAs NCQDs on GaAs(001),
(b) corresponding electron diffraction pattern.