Quantum-confinement effect in individual Ge_(1-x)Sn_x quantum dots on Si(111) substrates covered with ultrathin SiO_2 films using scanning tunneling spectroscopy

摘要

The authors observed a quantum-confinement effect in individual Ge_(1-x)Sn_x quantum dots (QDs) on Si (111) substrates covered with ultrathin SiO_2 films using scanning tunneling spectroscopy at room temperature. The quantum-confinement effect was featured by an increase in the energy band gap of ～1.5 eV with a decrease in QD diameter from 35 to 4 nm. The peaks for quantum levels of QDs became broader with a decrease in the height-diameter aspect ratio of QDs, demonstrating the gradual emergence of two dimensionality in density of states of quasi zero-dimensional QDs with the QD flattening.