A theoretical analysis of HREM imaging for 〈110〉 tetrahedral semiconductors

A theoretical analysis is presented of the intensity contrast in high resolution electron micrographs of tetrahedral semiconductor crystals. Particular attention is focussed on the respective roles of the linear and nonlinear scattering and interference processes. The relative contributions of these effects to the occurrence of sub-unit-cell image detail, such as the well-known dumbbell contrast in [110] Si, is examined in depth. It is shown that, in general, the complexity of the imaging process prevents such detail, which is beyond the Scherzer resolution limit, from being interpreted in terms of crystal structure. For crystals with sphalerite structure, the image interpretation is even more complex, although a possible strategy for identification of the two sub-lattices in such structures is explored.