Grazing Incidence X-Ray Diffraction Measurements of InAs/GaAs Quantum Dots Using Equipment Available for Laboratories

摘要

The technique to acquire internal information of self-assembled quantum dot (QD) has been paid considerable attention since complete control of QD structure is important for the development of QD devices. Using equipment available for laboratories, we have succeeded to evaluate the lattice constant distribution inside self-assembled QD and its crystal orientation dependence by the grazing incidence X-ray diffraction (GIXD) measurement. Two types of QD were prepared: one is a columnar QD fabricated via direct perpendicular stacking of Stranski-Krastanow (SK)-type QDs, and the other is a SK-type QD embedded in InGaAs strain-reducing layer. Using an imaging plate for a detector, we observed that QD-related signals appeared around a GaAs(220) peak, and extended in the direction of the 20 axis. We found that the lattice constants and their orientation dependence at the top and bottom of the QDs depend on the height in a columnar QD and on the indium composition of strain-reducing layer in a InGaAs-embedded QD. Symmetry of the in-plane lattice constant and that of photoluminescence polarization were found to have clear correlation in both QDs. The GIXD evaluation in laboratories will enhance the speed of the development of QD devices.