| Abstract Scope |
We have used first principles density functional theory to report on the effects of S doping on the mechanical and optoelectronic properties of the Cu2CdGeSe4 in it’s two known crystal structures. Computed lattice parameters (a,b,c, in Å) and band gaps (E_g, in eV) of tetragonal (I-42m) Cu2CdGeSe4 (a=5.85,c=11.25,E_g=1.18), orthorhombic (Pmn21) Cu2CdGeSe4 (a=6.70,b=6.99,c=8.21,E_g=1.26), and orthorhombic Cu2CdGeS4 (a=6.36,b=6.63,c=7.78,E_g=1.85) match well with experimental values: (a=5.75,c=11.12,E_g=1.20) for tetragonal Cu2CdGeSe4, (a=6.60,b=6.88,c=8.06,E_g=1.27) for orthorhombic Cu2CdGeSe4, and (a=6.30,b=6.56,c=7.71,E_g=1.93) for orthorhombic Cu2CdGeS4. Additionally, our calculations predict that the tetragonal-phase Cu2CdGeS4 should be stable, although no reports of this material exist. The computed formation energy for tetragonal phase is lower than orthorhombic. This ordering of energies is consistent with experimental observation that the growth temperature for the tetragonal phase reported is 200 ℃ lower than orthorhombic. Our optical property calculations and band gap values imply that this system could be suitable for applications as a solar cell absorber material. |