Lattice deformation and potential effects on linear and nonlinear optical properties of doped SiGe quantum dot encapsulated in Si matrix

Electron states in spheroid Si_0.7Ge_0.3 quantum dots are investigated taking into account the presence of a donor impurity atom and a weak external electromagnetic laser field. The conduction band confining profile along the radial direction is modelled by a parameterized exponential potential. Based on the calculated inter-state transition energies, the nonlinear optical responses associated with light absorption, relative refractive index change, and second and third harmonics generation are evaluated and discussed. Results are reported considering different positions of the donor center in the dot as well as for different values of the exponential potential parameter. When the impurity is shifted to different position, the polarisation changes inside the dot and hence the energy and wave function of the system. The change of impurity position from center to edge of the dot causes redshift whereas the increase in potential parameter causes blueshift.