Towards automated design of quantum cascade lasers

Abstract

We present an advanced technique for the design and optimization of GaAs/ AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier-phonon and carrier-carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of ϳ 9 m GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures.

Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers

“…Normalization is chosen such that occupations n i are dimensionless and add up to one in a given stage. The figure of merit is proportional to the modal gain of the device [21] and is a measure of the device performance.…”

“…Electron transport in GaAs-based quantum cascade lasers in both mid-IR and THz regimes has been successfully simulated via semiclassical (rate equations [19][20][21] and Monte Carlo [22][23][24][25]) and quantum techniques (density matrix [26][27][28][29][30], nonequilibrium Green's functions (NEGF) [31], and lately Wigner functions [32]). InP-based mid-IR QCLs have been addressed via semiclassical [33] and quantum transport approaches (8.5-µm [34] and 4.6-µm [35,36] devices).…”

Genetic algorithm applied to the optimization of quantum cascade lasers with second harmonic generation

“…17 so that it includes photon density equations. The inclusion of equations that describe single and double-photon stimulated emission processes will significantly add to the complexity of the numerical procedure and makes the achieving of convergence of the system more challenging.…”

“…This model needs to include all relevant scattering mechanisms that take place in both the optically active and collector (extractor)/injector multi-QW regions of the QCL, 17,18 as well as the processes describing the stimulated and simultaneous double photon absorption that occur between the second harmonic generationrelevant levels.…”

Charge Carrier Transport in Quantum Cascade Lasers in Strong Magnetic Field

“…LLs are magnetically tunable and, depending on their configuration, phonon emission is either inhibited or resonantly enhanced. This leads to a strong modulation of the population inversion and consequently the optical gain, as a function of magnetic field.We have previously developed an automated design procedure for structural parameters optimization of the active region of mid-infrared quantum cascade laser, with the goal of maximizing the output properties, in particular the optical gain, at predefined wavelengths compliant with selected application [4][5][6][7][8]. In mid-infrared devices, the desired emission wavelength imposes the required separations between the active laser energy states, while the spacing between the lower laser level and the ground state is set by the LO phonon energy (which facilitates the population inversion by allowing the fast emptying of the lower laser state by means of nonradiative transitions).…”