Blue shift in photoluminescene of semiconductor nanostructures

• Main Author: Khin, San Thit.
• Other Authors: Sun Changqing
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Semiconductors
• Online Access: http://hdl.handle.net/10356/17264
• Institution: Nanyang Technological University

With rapid developments in nanocrystals synthesis technologies, the size and dimensionality of nanocrystals can be manipulated in a controlled fashion. As a result, an understanding of the size-dependence of bandgap energy is one of the most important topics in nanostructure studied. The band structure of a nanometric semiconductor changes: the band gap expands, the core level shifts, the bandwidth revises, and the sublevel separation within a band increases. Because of band gap expands with reducing particle size, which gives rise to the blue shift in the photoluminescence (PL) and photoabsorbance of nanometric semiconductors such as Si, Si oxides, III-VI semiconductor (GaN, GaP, GaAs, InP and InAs) and II-Vl semiconductor (CdS, CdSe, CdTe, ZnS, ZnSe and ZnTe) compounds. In this project, studying of Photoluminescence blue shift of semiconductor nanomaterials both experimentally and theoretically, leading to a conclusion that a recent ‘bond order-length -strength’ (bond-OLS) correlation mechanism [J. Phys. Condens. Matter (2002)] is necessary. The bond-order-length-strength (BOLS) correlation indicates that the atomic coordination imperfection causes the remaining bonds of the under-coordinated atom to contract spontaneously associated with bond strength gain and the interatomic trapping potential well depression. This project also involved the study of the entire band structure such as the band gap expansion, core-level shift, Stokes shift (electron-phonon interaction), and dielectric suppression (electron polarization). The experiment results were obtained from different sources to verify the predictions of the models, and to study the effects of size and thickness of nano materials. Analysis of the calculated data will also be discussed in details.