  A novel design-friendly device called the transistor-injected dual doping
quantum cascade laser (TI-D2QCL) with two different doping in each stack of a
homogeneous superlattice is proposed. By adjusting the base-emitter bias Vbe of
the bipolar transistor to supply electrons in the dual doping regions, charge
quasi-neutrality can be achieved to generate different optical transitions in
each cascading superlattice stack. These transitions are then stacked and
amplified to contribute to a broad flat gain spectrum. Model calculations of a
designed TI- D2QCL show that a broad flat gain spectrum ranging from 9.41um to
12.01um with a relative bandwidth of 0.24 can be obtained, indicating that the
TI- D2QCL with dual doping pattern may open a new pathway to the appealing
applications in both MIR and THz frequency ranges, from wideband optical
generations to advanced frequency comb technologies.
