Modeling of the electrically-tunable transistor-injected quantum cascade laser

A detailed quantum mechanical model that assesses the mid-infrared (MIR) and terahertz (THz) wavelength tunability of a three-terminal Transistor-Injected Quantum Cascade Laser (TI-QCL) is presented. It is shown that the device injection efficiency can be considerably enhanced by inserting an i-n layer between the QCL and the base of the transistor to match the quantum impedance between the two regions. Our calculations based on the Schrodinger equation with complex potential boundaries indicate that cascading lasing occurs when charge quasi-neutrality in the superlattice (SL) is achieved with an injection current density of 4.71 kA/cm², which is comparable to the values obtained in conventional two-terminal QCLs. Our analysis of the transition dipole moments between various quasi-bound states in the QCL SL suggests that the lasing wavelength can vary over a few microns as a function of the electric field at constant current, which indicates that the TI-QCL has potential for tunable MIR and THz sources. Finally, simultaneous multi-color lasing with wide energy separation is anticipated with application in MIR multi-gas detection.