First-Principles Study On The Au/Bi Doped-HgCdTe

In recent years, with the rapid development of infrared technology, the structural and optical-electrical characteristics of infrared detector has attracted a lot of attention. However, the precision of infrared detectors is limited by the electrical properties, size and uniformity parameter of materials. MCT is the most important and versatile material for detector applications over the entire IR range, due to its advantages like lower concentration of the intrinsic carrier, lower surface state density, smaller dielectric constant and larger optical absorption coefficient. N-type doping of Hg1-xCdxTe was achieved easily by indium in situ substituting mercury, whose carrier concentration can be very high. However, well-controlled p-type doping is still one of the most serious bottlenecks in MCT-based detector technology currently. For p-type doped MCT, group I elements and group V elements are the most familiar dopants. Because of the lower diffusion coefficient, the structure of Au doped-HgCdTe is very stable. Au produces a shallow energy level at the top of the valence band, which acts as an acceptor. Therefore, Au is an effective p type dopant. The component x has great influences on the electronic structure and electrical properties of HgCdTe. But, comprehensive investigations should be taken on the relationships between component x and bonding mechanism, electrical properties. The group V impurities Bi shows a complicated amphoteric behavior in HgCdTe, that in situ substitute the cation Hg behavior as n-type and in situ substitute the anion Te behavior as p-type. There are no relevant studies in Bi doped-HgCdTe by first-principle calculations. The main study contents and the main innovations of this dissertation include:In this paper, by first-principles calculations based on DFT with a modified Heyd-Scuseria-Ernzerhof hybrid exchange-corrector functional, the characters of Hg1-xCdxTe, Au doped Hg1-xCdxTe and Bi doped-Hgo.75Cdo.25Te were calculated. Based on the results, effects of component x on Au doped Hg1-xCdxTe have been analyzed. At the same time, the doping effects of Bi in Hgo.75Cdo.25Te have also been studied. The main contents of this dissertation are as follows:(a) By first-principles calculations, Structural relaxations, charge densities, electron localization functions (ELFs), density of states (DOSs) and band structures were obtained to reveal dopant stability and doping efficiency. The fairly stability of Au doped-Hg1-xCdxTe (x=0.25, x=0.5, x=0.75) has been discussed, and Au-Te bonds weaken with the increase of Cd composition. On the other hand, Au produces a shallow energy level at the top of the valence band, which indicates an efficient dopant of p-type doping. The effects of impurity energy levels on VBM are more obvious than that of Hgo.25Cdo.75Te, which result in the more efficient p-type doping. In addition, for both Hg1-xCdxTe and Au-doped Hg1-xCdxTe, the linear relationships between band gaps and Cd composition are presented.(b) By first-principles calculations, structural relaxations, charge densities, electron localization functions (ELFs), density of states (DOSs)、band structures and band decomposed charge density were obtained to reveal dopant stability and doping efficiency. The results indicate that Bi in Hgo.75Cdo.25Te is fairly stable. Bi shows similar characteristics as those of the other group V elements, that in BiTe behaviour as p-type dopants and in BiHg behaviour as n-type dopants.