The effects of aluminum concentration and hydrogenic donor impurity on the linear and nonlinear optical properties of a GaAs spherical quantum dot confined at the center of a Ga1−xAlxAs cylindrical nano-wire

Abstract

The energy eigenvalues and corresponding wave functions of four first lower-lying states of a GaAs spherical quantum dot which is located at the center of a Ga1−xAlxAs cylindrical nano-wire are calculated using finite difference approximation within the effective mass framework. The reliability of calculated wave functions is checked by computing orthogonality and comparing with similar reported results. In addition, the oscillator strength, linear and third-order nonlinear optical absorption coefficients and refractive index changes are calculated based on optical 1–2, 2–3 and 3–4 transitions by means of the compact density-matrix approach, with and without hydrogenic donor impurity. The effect of aluminum concentration on the optical properties is also investigated. The results show that the presence of impurity has great influence on optical properties of the system and shifts optical spectrum towards higher energies. Moreover, through increasing the aluminum concentration both blue and red shifts appear in optical spectrum, which are strongly affected by energy levels between which transition may occur and presence or absence of impurity. Additionally, the calculated results also reveal that the magnitude of absorption coefficient, refractive index changes and oscillator strength as well as the saturation in optical spectrum depend on the aluminum concentration and presence of impurity for all transitions.