Effect of beryllium doping and vacancy in band structure, magnetic and optical properties of free standing germanene

Ab initio calculations of electronic, magnetic and optical properties of defected (beryllium (Be) doped or void induced) buckled free standing (FS) germanene have been explored. Concentrations of doping as well as vacancy (keeping a fixed low amount of Be) are increased thoroughly, in order to study the modifications of different physical properties critically. Our study reveals that, incorporation of doping and void destroy Dirac cone in band structure of germanene. Finite bandgap for the requirement of field effect transistor (FET) applications is obtained in case of semiconducting configuration with 15.62% doping concentration. Magnetism is also induced for doping of Be with high concentration only, which is supported from projected density of states (PDOS) and charge density analysis. Anisotropic effects are prominent in optical properties like dielectric functions, absorption spectra, reflectivity and its modulation and conductivity. Static real part of dielectric constant increases linearly with increase in doping concentration but decreases with increase in vacancy concentration considering parallel polarization of electro-magnetic (EM) wave. Predicted computational results of plasma frequencies are in well agreement with expected analytical data. Peak corresponding to maximum intensity of electron energy loss spectra (EELS) appears at the position of plasma frequency in case of every structure. We expect, this study may help for better understanding of next generation germanene based nano-technology.