Size, shape and composition of an In(Ga)As quantum dot. The percentages indicate the fraction of InAs, and reveals that it increases vertically from 70% at the base center to 100% at the top center. In addition, horizontally the fraction InAs decreases to 25% at the base edge, evolving in a 22.5% 7 monolayer thick wetting layer. The solid line depicts the ellipsoidal shape of the QD
“We were surprised to find that the shape and composition deviate strongly from those which are usually used”, says Janneke Blokland, PhD student at the Nijmegen High Field Magnet Laboratory (HFML) and first author of the paper. “The dots have an ellipsoidal shape and turned out to be much taller and with a stronger indium gradient than expected”. The report was very interesting since both the optical and electrical properties of the ellipsoidal QDs were earlier determined and reported in a Physical Review B paper “Hole levels in InAs self-assembled quantum dots”. “This is the first time that structural and spectroscopic properties of quantum dots are experimentally combined”, says Peter Christianen, associate professor at the HFML Nijmegen. According to Christianen, spectroscopic data was only recently explained by theoretical models with the use of the QD dimension and composition as fitting parameters. “These simple models resulted in dot parameters that are really different than the ones we have found now” explains Christianen to Nanospotlight. “With our unique combination of spectroscopy and X-STM experiments on the same QDs, we make it possible to really test advanced theoretical models to understand the underlying physics at the nanoscale and use this knowledge to improve the performance of future devices”.
Kimberly Annosha Sablon