We study the operation of an 8.5 µm quantum cascade laser based on GaInAs/AlInAs lattice matched to InP using three different simulation models based on density matrix (DM) and nonequilibrium Green's function (NEGF) formulations. The latter advanced scheme serves as a validation for the simpler DM schemes and, at the same time, provides additional insight, such as the temperatures of the sub-band carrier distributions. We find that for the particular quantum cascade laser studied here, the behavior is well described by simple quantum mechanical estimates based on Fermi's golden rule. As a consequence, the DM model, which includes second order currents, agrees well with the NEGF results. Both these simulations are in accordance with previously reported data and a second regrown device
We study the impact of interface roughness on the operation of mid-IR and THz quantum cascade lasers. Particular emphasis is given towards the differences between the Gaussian and exponential roughness distribution functions, for which we present results from simulation packages based on nonequilibrium Green's functions and density matrices. The Gaussian distribution suppresses scattering at high momentum transfer which enhances the lifetime of the upper laser level in mid-IR lasers. For THz lasers, a broader range of scattering transitions is of relevance, which is sensitive to the entire profile of the interface fluctuations. Furthermore we discuss the implementation of interface roughness within a two band model.
Johnson and shot noises are usually considered as independent in intersubband detectors. In this paper, we discuss some simple ideas showing that they are actually the equilibrium and far from equilibrium limits of a single phenomenon. We present an intuitive framework to consistently understand and model these noises in unipolar detectors, in order to enlarge the toolbox of quantum designers.
The aim of this article is to determine the best dielectric between SiO2, Si3N4 and TiO2 for quantum cascade laser (QCL) passivation layers depending on the operation wavelength. It relies on both Mueller ellipsometry measurement to accurately determine the optical constants (the refractive index n and the extinction coefficient k) of the three dielectrics, and optical simulations to determine the mode overlap with the dielectric and furthermore the modal losses in the passivation layer. The impact of dielectric thermal conductivities are taken into account and shown to be not critical on the laser performances.
We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm-1 with 60 cm-1 tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5µm.The need for broadly tunable sources for Mid-Infrared spectroscopy has been identified for years. In order to detect a complex molecules or a set of simple molecules, one needs a source with a small line width and tunable over a few tens of wave numbers. External cavity sources are already available but with limited performances and cost reduction potential. Distributed Feedback (DFB) Quantum Cascade Lasers (QCL) is one of the favored sources for the Laser Spectroscopy ]. We propose here a monolithic tuneable source which is very appealing because of the compactness, the robustness and the usability. A single DFB QCL has a limited tuning range, the two main leverages being the temperature via external temperature control (slow tuning) and via the current (Fig. 1 right).
Electronic noise in quantum cascade structures is investigated theoretically and experimentally under dark conditions. A model based on a unified and insightful vision of noise generating mechanisms is proposed and describes both thermal and shot noise behaviors. Dark measurements of quantum cascade detectors operating at 8 μm and 15 μm are retrieved with good quantitative agreement. This model is expected to be applicable to other quantum structures and under illumination.
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