First-principles Study Of The Electronic Structure Of Hg_1-xCd_xSe

As rapid advance in the infrared technology,military and civilian fields have higher demand on infrared materials.As the third generation infrared detector materials,Hg_1-xCd_xSe attributes similarity with Hg_1-xCd_xTe.The band-gap of Hg_1-xCd_xSe changes within the range of-0.2¹.74eV,covering the whole infrared bands.It is lattice matching with some mature and large areas'III-V substrate materials,with smaller lattice mismatch,low dislocation density and small expansion coefficient.Hg_1-xCd_xSe becomes an important and potential application material in the field of long-wavelength infrared detection.At present,most of the studies on selenium-cadmium-cadmium concentrate on the experimental aspects,and there are few reports on the relevant theoretical calculations.More importantly,the Cd concentration of the experiment was concentrated in the low concentration range,and there was no systematic studies within the range of 0 to 1 concentrations.Therefore,in-depth study of the structure and properties of HgSe and CdSe,and study of Hg_1-xCd_xSe material are necessary.In this paper,intrinsic mercury selenide?HgSe?and cadmium selenide?CdSe?are taken as the starting points to study the changes of the band structure,optical properties,etc.,under the strain conditions and their stability under equilibrium volume.Then,different concentrations of Cd are doped to mercury selenide,and the changes in geometry and stability of Hg_1-xCd_xdSe after doping are discussed.Theoretical calculations of its band structure,electronic structure and optical properties are conducted to study the effect of doping on mercury selenide.In this paper,the basic physical properties of the crystal structure are calculated by the the GGA-PBE method based on the first-principles density functional theory using CASTEP module in Materials Studio software.Comparingthecalculationresults,thecharacteristicsofthe selenium-cadmium-mercury obtained provide a certain theoretical prediction for the experimental study.The main research contents and results are as follows:?1?The lattice parameters,band structures and optical properties of HgSe and CdSe under zero pressure,compressive strain and tensile strain are calculated respectively,and the effects of strain on physical properties and optical properties are clarified.Calculations proves that:Since HgSe and CdSe both include sp³ and p-d orbitals hybridization in the bonding features,the changes of lattice constants of the two are the same and the macroscopic changes in the material system under strain conditions are obtained when the tensile and compressive stresses are applied respectively;In the band structures,the d-state energy level of the Hg atom is shallower,and the d-state energy level of the Cd atom is deeper;Under the same strain conditions,the energy level extension in HgSe is severer than that in CdSe,leading to no significant change in the conduction band bottom in HgSe;The final result is a greater change in the bandgap of CdSe than HgSe;The Hg atom and the Se atom,the Cd atom and the Se atom mainly form a covalent bond and contain a certain ionic bond component,and the pressure is mainly applied to increase the charge aggregation degree;The ionic bond component in the bonding characteristic is enhanced,applying tensile force to enhance covalentness.When the compressive strain is applied,the static dielectric constants of HgSe and CdSe decrease,and the absorption in the infrared band is enhanced;In contrast to tensile strain,it is consistent with changes in the band structure;There are no imaginary frequencies in the phonon spectra of HgSe and CdSe,and the stable structures of the two compounds are obtained.?2?The crystal structures,electronic structures and optical properties of Hg_1-xCd_xSe in the range of 0 to 1of x in 0.125 steps are calculated;The effects of different concentrations of Cd on Hg_1-xCd_xSe are clarified;Calculations proves that:Although the Hg atom radius is larger than the Cd atom,the electronegativity of Hg is stronger than the Cd atom;In the substitution doping of Cd,lattice distortion and slight volume expansion occur in all Hg_1-xCd_xSe models in the range of0 to 1of x;With the increase of Cd atom doping concentration,the total energy,the formation energy,the binding energy of Hg_1-xCd_xSe are gradually reduced,and the stability is gradually enhanced;Because the sp³ and p-d orbitals hybridization between the Cd and Se atoms are weakened,the bandgap of Hg_1-xCd_xSe becomes larger as the Cd concentration increases;With the increase of Cd concentration,the lower valence band moves toward high energy,and the density of p orbital states at the top of the valence band decreases;The bottom of the conduction band is obviously moved up;The static dielectric constant decreases as the concentration of Cd increases,and the electronic transitions between different valence bands and conduction bands produce different optical properties;The absorption band-edge is blue-shifted,but there is still a high absorption rate(>10⁴cm^-1)in the wavelength range from 800 to 1700 nm;When the low concentration of Cd is doped,there is a high absorption rate in the middle-far infrared region,which increases the light absorption range of the infrared region.