Transmission electron microscopy of semiconductor quantum dots

We report on plan-view transmission electron microscopy techniques, by which the size, the actual shape and the strain of a coherent quantum dot in semiconductor heterostructures can be measured very accurately. The bright-field suppressed-diffraction imaging condition where no strong diffracted beam is excited in the sample provides reliable size measurement. Using suppressed-diffraction imaging condition, the intensity contour in a coherent island is related to the height, and thus the detailed shape and the aspect ratio can be extracted. The strain contrast of a coherent island imaged using an exact two-beam dynamical diffraction condition is useful for strain measurement and the corresponding features is related to the shape of an island. The physical origins and accuracy of interpretation of the image contrast are discussed, using the simulations and experimental examples.