The First Principle Study On The Amorphous Infrared Photoelectronic Material PbS

Amorphous semiconductor is one of the most important parts in the condensed matter physics. It has been found that the amorphous semiconductor compound PbS has a great advantage in the infrared detector, specially in the highly integrated infrared detectors. Recently detectors synthesized using PbS and its alloy materials have been of great interest because of their high detected sensitivity compared with the best detectors found now.The calculation and simulation of amorphous semiconductors can be used not only in analysis and explanation of the uncertainty experimental results, but also in the prediction of new phenomenon. It is of vital importance in the fundamental understanding of the basic problems in the solid state physics and in the fabrication of new devices.Using the CASTEP developed by Cambridge Univesity, we have studied the electronic properties of bulk PbS, and predicted the surface geometry structure and electronic structure of PbS(-100) surface with and without vacancy defects by means of the first principle theory, the primary content of this thesis is composed the following three parts: i ) Based on the first principle method, the calculations of the total energy and the equilibrium lattice constant for the PbS (CsCl, ZnS and NaCl) compound have been performed within different exchange correlation potentials (DECP) on both the generalized gradient approximation (GGA) and the local density approximation (LDA). The effects of DECP on the band structure, the density of states, the partial density of states and the band gap are discussed. LDA give a better band gap, while GGA give a better lattice parameter. The energy calculation shows that the NaCl structure is found to be the most stable one than that of other two structures.ii ) We have performed the calculation of electronic properties and structural properties of PbS(-100) supercell without defects as our reference criterion. The electronic properties and structural properties of both Pb and S vacancy defects in PbS(-l00) with total 36, 48 and 64 atoms have also been studied using first-principle theory. The result of the structural optimization shows that there are no reconstruction in the cleaned PbS (-100) surface, but there are relaxation in the surface layers. Using the results of band structures and DOS, we explained the electronic structures and the characteristic of geometry relaxation. The S vacancy defects cause the whole DOS shift downward, while the Pb vacancy defects cause the whole DOS shift upward. S vacancies are positively charged and act as donors, thus the PbS(-100) system act as n type semiconductors, however Pb vacancies are negatively charged and act as acceptors and the system act as p type semiconductors. The more the numbers of vacancies, the larger the shift of the total DOS is.iii) Finally, a brief conclusion of our work was given.