Study On Al Doped Semiconductor Mg₂Ge

Semiconductor germanide Mg₂Ge has the advantages of high thermal stability,low density,excellent compressibility,rich availability,non-toxic and pollution-free,and has a good application prospect in the fields of thermoelectricity and optoelectronics.In this paper,the electrical and optical properties of intrinsic Mg₂Ge and al-doped Mg₂Ge are studied theoretically,and the crystal structure and surface appearance of Mg₂Ge with different substrates and different Al doped concentrations are studied experimentally.Firstly,the electronic structure,state density,elastic constants and photoelectric properties of Mg₂Ge are calculated by using the first principle of density functional theory.The results show that Mg₂Ge is an indirect bandgap semiconductor,and the bandgap is 0.2136e V.The valence band of Mg₂Ge is mainly composed of Ge 4s and 4p electrons,and the conduction band is mainly composed of Mg 3s and 3p electrons and Ge 4p electrons.The static dielectric constant is 25.294,and the refractive index is 4.5043.The maximum peak value of the absorption coefficient is 396,560.9 cm^-1.The brittleness of Mg₂Ge is explained by elastic constants.Secondly,the electronic structures and optical properties of Mg₂Ge at different Al doped concentrations were calculated by using the first principle of density functional theory.Four doping models of Mg_2-xAl_xGe?x=0,0.125,0.25,0.5?were established.The calculation results show that the Al-doped Mg₂Ge Fermi level enters the conduction band and exhibits n-type conductivity characteristics.After doping,the conduction structure near the Fermi energy level of Mg₂Ge was changed to be composed of Al 3p electrons,and Ge 4s electrons and Mg3s,3p electrons.The static permittivity and refractive index increase.The absorption spectrum is redshifted and the maximum absorption coefficient decreases slightly.The peak value of photoconductivity is obtained when x=0.125.The blue shift occurs in the energy loss function,and it is most obvious when x=0.125.Finally,Mg₂Ge films with different Al doped concentrations were prepared on Ge substrate,sapphire substrate and quartz substrate by magnetron sputtering apparatus and annealing furnace.The crystal structure and appearance of the film were characterized by XRD and SEM.The results showed that Mg₂Ge films with single phase were grown on the three substrates.Although the intensity of Mg₂Ge diffraction peak was changed by Al doping at different concentrations,the crystal structure of Mg₂Ge films was not affected.The Al is present in the Mg₂Ge film in the form of substitution and the surface roughness of the film increases.In addition,due to the epidemic situation,it was impossible to return to school,and some optical property test data were not given.