Enhancement of transition lifetime, linear and nonlinear optical properties in laterally coupled lens-shaped quantum dots for Tera-Hertz range

In this paper, we theoretically study the effects of the structural dimensions, pressure (P) and temperature (T) on transition lifetime (τ), on the linear (α(1)), nonlinear (α(3)) and total α absorption coefficients for Tera-Hertz range (1.2-2.88 THz). The structure under investigation consists of two laterally coupled InAs/GaAs lens-shaped quantum dots (LCQDs) connected to a wetting layer. This structure is analyzed by using the Finite Difference Method (FDM) and the effective mass approximation. The analytical expressions of the transition life time, linear, nonlinear and total absorption coefficients are discussed by using the density matrix formalism. Obtained results show that the total absorption coefficient achieves a maximum value in Tera-Hertz range and the resonant peaks shift toward the lower energies (higher) by increasing the pressure (temperature). Also, the transition lifetime decrease (increase) by increasing the temperature (pressure). As well, the spacer width (between quantum dots) effect is well studied and can be controlled and adjusted. This theoretical study gives a new degree of freedom in describing devices based on laterally coupled QDs and on the intra-band transitions of electrons to achieve desired nonlinear optical properties in Tera-Hertz field.