US group analyses CdTe crystal dislocations
Semiconductor crystal irregularities (known as dislocations) govern many aspects of a material's behaviour from their roles in the way crystals form to their effects on a material's mechanical, thermal and opto-electronic properties.
But despite the large amount of theoretical work in this field, experimental knowledge detailing the atomically resolved chemical structure of even the most basic dislocations has only just begun to be accessible.
A group of American scientists from the University of Illinois at Chicago and Argonne National Laboratory has now combined state-of-the-art atomic-resolution Z-contrast imaging and X-ray spectroscopy in a scanning transmission electron microscope (STEM) to analyse two low-elastic-energy stair-rod dislocations in the binary II-VI semiconductor CdTe.
CdTe is commercially used in thin-film photovoltaics owing to its ideal electrical properties. And yet the conversion efficiency of CdTe solar cells, which is critical for the industry, has only seen minor developments and improvements over the last 20 years despite intense research activity. Current laboratory records are still shy of the theoretical limits quoted as far back as 1961.
In the current issue of Acta Crystallographica Section A: Foundations and Advances, the researchers demonstrate how, with the use of atomic-resolution STEM images and specially tailored Burgers circuits, the structure of these dislocations can now be identified. Pictured above is an image of an isolated 30° partial dislocation with Te core.
According to the researchers, the results may lead to the eventual improvement in the conversion efficiency of CdTe solar cells. The analysis presented can also be applied to study and predict similar structures in other zinc-blende and diamond materials. This study further demonstrates how the new generation of aberration-corrected electron microscopes can advance our understanding of seemingly basic crystal-structure defects.
'Atomic scale study of polar Lomer-Cottrell and Hirth lock dislocation cores in CdTe' by Paulauskas et al, appears in Acta Cryst. (2014) A70; doi:10.1107/S2053273314019639]
