Band Gap Modulated By Strain In Semiconductor Nanostructures

In recent years,"strain engineering" in nanomaterials and nanostructures can effectively modulate the physical and chemical properties, which becomes one of the focus topics in the fields of material sciences and condensed matter physics. It is generally known that the nanosystems will be in self-equilibrium state as the consequence of high surface-to-volume ratio (SVR) and coordination imperfection, and the lattice strain will be taken place and further affect the related performance. In addition, other external fields such as temperature and pressure stimuli would also effectively tune the properties.Based on the recently-developed bond-length and bond-energy correlation, we study the effect of strain both in self-equilibrium state and some external fields approach on the band gap shift in semiconductor nanostructures, including nanocrystals and nanowires. Also, we put forward the deformation potential relations. The achievements are shown as follows:1. We study the size-dependent band gaps in SnO2nanowires and nanocrystals in terms of bond-length and bond-energy correlation and discuss the relationship between strain and band gap shift from the point view of deformation potential. It has been found that the SVR plays the crucial role for the band offset on solid size. The self-equilibrium strain induced by surface atomic layers contraction is the physical origin of band gap variation.2. The size-and temperature-dependent band gap shift in ZnSe nanostructures has been established. The theoretical study shows that the self-equilibrium strain and thermal strain have important impact on band gap shift in nanomaterials. The external fields lead to the change of single bond-energy and influence the interaction among atoms. In particular, the contributions from nanosize effect and high temperature present a competitive role for band gap shift.3. We developed an analytical model to explore the edge effects in Si nanowires with different kinds of cross-sections on band gap shift. It was found that the abnormal atom energy state in the edges would affect the band structure of Si nanowires with various transverse cross-sections, such as circle, hexagon, rectangle, and triangle. Our results show that the deformation potential in Si nanowires with triangular cross-sections has the largest among those of the other cases at a fixed strain. The model predictions are well agreement with the available experimental evidences, which provides an underlying mechanism for the modulation of optical-electronic properties in nanodevices.