Study of an application of non-parabolic complex band structures to the design for mid-infrared quantum cascade lasers

Abstract

We have investigated the influence of nonparabolicity both of an imaginary band located in a bandgap and of a conduction band to improve the accuracy of energy levels for the design of GaInAs/AlInAs mid-infrared quantum cascade lasers (QCLs). The lasing wavelength of the QCL obtained experimentally was compared to that of the calculated optical gain peak by utilizing the single-band non-equilibrium Green's function (NEGF) method. We calculated the energy-dependent effective mass of electrons used in the NEGF calculation from the complex band structure of each bulk material forming the QCL. In a widely lasing wavelength range of 5–10 μm, the calculated gain peaks of the QCLs each agreed very well with the lasing wavelengths obtained experimentally. We have confirmed that in designing the QCL structures, energy dependency of the energy effective mass in the complex bands is significant.