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The extension of the operating frequency of Quantum Cascade Lasers (QCL) into the 20-50 μm regime is a desirable goal as it would bridge the gap between mid-infrared and THz devices. Coherent light emitters in this spectral range are also needed for spectroscopy and radio astronomy applications. Since little attention has been devoted to the subject in the past, we investigate the dominant loss mechanisms of QCLs in this spectral range. We report on an InGaAs/InAlAs QCL in an InP dielectric waveguide emitting at 23 μm wavelength whose electroluminescence spectrum shows an anomalous low-frequency cut which prevents laser action at low electric field. We also observe similar line shape in other GaAs/AlGaAs devices. The spectral features are analyzed and explained in terms of refractive index anomalies induced by phonon resonances. [ABSTRACT FROM AUTHOR]

We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0° and 50° was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers. [ABSTRACT FROM AUTHOR]

We report the observation of transverse electric polarized electroluminescence from InAs/AlInAs quantum dash quantum cascade structures up to room temperature. The emission is attributed to the electric field confined along the shortest lateral dimension of the dashes, as confirmed by its dependence on crystallographic orientation both in absorption measurements on a dedicated sample and from electroluminescence itself. From the absorption, we estimate a dipole moment for the observed transition of = 1.7 nm. The electroluminescence is peaked at around 110 meV and increases with applied bias. Its temperature dependence shows a decrease at higher temperatures limited by optical phonon emission. [ABSTRACT FROM AUTHOR]

A photovoltaic InAs quantum dot-under-a-well photodetector is reported with a peak responsivity at 7 μm wavelength. In this structure, we implement an improved injection scheme, which allows a controlled feeding of the quantum dots through a modulation-doped InGaAs quantum well injector. A thin Al0.3Ga0.7As barrier significantly reduces the dark current and, at the same time, is responsible for the photovoltaic behavior. At 4 K and no applied bias, a responsivity of 2.5 mA/W and a detectivity of D*=2.3×1010 cm Hz1/2/W in the dark is measured. The TBLIP of the device is 60 K and the D* at this temperature is 2×109 cm Hz1/2/W. [ABSTRACT FROM AUTHOR]

We present a study of the dynamic properties of electrons tunneling from an InGaAs quantum well to self assembled InAs quantum dots. The experiments were conducted on three highly asymmetric quantum dot infrared photodetectors, where the quantum well and quantum dots were separated by a composite GaAs/AlGaAs/GaAs barrier, which varied from 3.5 nm to 7.0 nm. We performed interband (photoluminescence) and intraband (photocurrent) measurements to characterize the spectral properties of the well and the dots. The photoluminescence measurements revealed that the two nanostructures are decoupled when the device is at zero bias. By intraband pump-probe experiments and photocurrent saturation experiments, we were able to extrapolate a refilling time τ from the well to the dots, which varied from a few μs for the thinnest barrier and hundreds of μs for the thickest one. The extracted values are in good agreement with characteristic tunneling times computed by using a model based on the theoretically predicted transmission coefficient of the electrons through the composite barrier. [ABSTRACT FROM AUTHOR]