Author:   SHA YAN    2014-04-15

Heterocrystalline polytype structures have been intensively studied in recent years as novel types of superlattices. These polytype superlattices consist of chemically identical but structurally different materials, which match well at their interfaces.

The polytype superlattices would act as barriers for electron transport, leading to charge accumulation in certain regions due either to band offsets at the polytype interfaces, or spontaneous polarization in the polytype regions with asymmetrical structures.

The research group of Dr. Luying Li studied polytype heterocrystalline structures within InAs nanopillars using multiple TEM techniques in cooperation with related groups in Wuhan University and Arizona State University. The electric field related to spontaneous polarization within the zinc-blende region is revealed at the nanometer scale using off-axis electron holography. Through probe-corrected HAADF imaging, local values of spontaneous polarization are determined with atomic resolution, and their variations are related to strain-induced lattice distortions at the polytype interfaces. This improved knowledge and understanding of strain-induced variations of spontaneous polarization along the interface normal could provide valuable information for tailoring charge distribution in semiconductor nanostructures, which will help to control this process better as well as opening new pathways for fabrication of future devices. This work was evaluated as a very nice demonstration of what is achievable in a modern aberration corrected microscope by the reviewer.

This work was published in Advanced Materials (Adv. Mater 26, 1052-1057 (2014)), and was selected as ‘Research highlights’ by Nature Physics in the December Issue. This study was supported by National Natural Science Foundation of China (51371085, 11304106), MOE Doctoral Fund (20120142120059), the Fundamental Research Funds for the Central Universities (HUST: 2012QN107), SRF for ROCS, SEM.

Probe-corrected high-angle annular-dark-field image of specific InAs nanopillar, including multiple stacking disorder. Three regions of wurtzite structure are highlighted by yellow background with atomic scale spontaneous polarization effect, which is attributed to non-centrosymmetry of the unit cell structure