The Theoretical Study Of Electronic Structure And Optical Properties Of Lead Salts (001) Surface Structure

The IV-VI semiconductors PbS, PbSe and PbTe with the cubic Nad (rock salt) structure, generally known as lead salts, are narrow gap semiconductor compounds with strong ionic character. The unusual characteristics of lead salts, such as the high refractive index and the positive temperature coefficient of the gap. the large carrier mobility, make them unique among polar compounds and have important applications in many fields, such as infrared detectors, light-emitting devices, and more recently as infrared laser in fiber optics, thermoelectric materials, solar energy panel and window coatings. Studies about hetero-structures, films, quantum wires and quantum dots or wells of lead salts and their applications have caused much attention in the past decades. In addition, the impure lead salts possess better characteristics and are used in many fields. The surface of material is very important for us to use it, while the (001) surface of lead salts is a natural surface.Using the CASTEP developed by Cambridge University, we have studied the bulk properties of the three lead salts , such as lattice parameters, electronic structures and some optical properties, and predicted the surface geometry structures and electronic structures of PbSs PbSe and PbTe(OOl) surfaces by the first principle method. Some interesting results are list below:The lattice parameters of lead salts cell lattices, the energy band structurse and the density of electronic states, reflectivity and absorption we obtained are given in the paper. According to the band structures of the three salts, some optical properties and their origins are analyzed and interpreted. The characters of the optical spectrums depend mainly on the transitions between around the top of value band and conductor band.As for the surface geometry structures, there are no reconstruction in the cleaned PbS, PbSe, PbTe (001) surfaces, but there are different relaxation in the surface layers with an oscillatory pattern. The shifts of the interlayer distance and the intralayer rumpling show some regulations. The calculation of the surface electronic structuresof the three lead salts indicate that there are no surface states in the fundamental gaps while the surface resonance states appear mainly in the stomach gap in the value band and conductor band as well as near a deeper band.