PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS
Abstract
We study the details of electronic transport related to the atomistic structure of silicon quantum dots embedded
in a silicon dioxide matrix using ab initio calculations of the density of states. Several structural and composition
features of quantum dots (QDs), such as diameter and amorphization level, are studied and correlated with
transport under transfer Hamiltonian formalism. The current is strongly dependent on the QD density of states
and on the conduction gap, both dependent on the dot diameter. In particular, as size increases, the available
states inside the QD increase, while the QD band gap decreases due to relaxation of quantum confinement. Both
effects contribute to increasing the current with the dot size. Besides, valence band offset between the band
edges of the QD and the silica, and conduction band offset in a minor grade, increases with the QD diameter
up to the theoretical value corresponding to planar heterostructures, thus decreasing the tunneling transmission
probability and hence the total current.We discuss the influence of these parameters on electron and hole transport,
evidencing a correlation between the electron (hole) barrier value and the electron (hole) current, and obtaining
a general enhancement of the electron (hole) transport for larger (smaller) QD. Finally, we show that crystalline
and amorphous structures exhibit enhanced probability of hole and electron current, respectively.