H. C. Liu

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A new temperature performance record of 199.5 K for terahertz quantum cascade lasers is achieved by optimizing the lasing transition oscillator strength of the resonant phonon based three-well design. The optimum oscillator strength of 0.58 was found to be larger than that of the previous record (0.41) by Kumar et al. [Appl. Phys. Lett. 94, 131105 (2009)].(More)
We characterized a set of terahertz quantum-cascade lasers with identical device parameters except for the doping concentration. The ␦-doping density was varied from 3.2ϫ 10 10 to 4.8ϫ 10 10 cm −2. We observed that the threshold current density increased monotonically with doping. Moreover, the measured results on devices with different cavity lengths(More)
In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were(More)
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. We experimentally investigated the effect of oscillator strength (radiative(More)
The density matrix based model is employed to design number of THz quantum cascade lasers with various laser transition oscillator strengths. The optimum oscillator strength varies between 0.35 and 0.47. Experimental results verify the theoretical predictions.
We designed and demonstrated a terahertz quantum cascade laser based on indirect pump injection to the upper lasing state and phonon scattering extraction from the lower lasing state. By employing a rate equation formalism and a genetic algorithm, an optimized active region design with four-well GaAs=Al 0:25 Ga 0:75 As cascade module was obtained and(More)
An electrically controlled beam pattern technique for semi-insulating surface plasmon terahertz quantum cascade is presented. The near field and far field measurements confirm that the lasing THz beam is maneuvered by 25&#x00B0; in emission angle, when the current density changes from 1.9 kA/cm<sup>2</sup> to 2.3 kA/cm<sup>2</sup>.
In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: Keywords: Infrared Split-off band PbS quantum dot Tunneling quantum dot Room(More)
A GaAs/AlGaAs detector is demonstrated showing multiple detection capabilities. This detector exhibits a broad spectral response in the 200-870 nm (ultraviolet-visible) range for forward bias and in the 590-870 nm (visible) range for reverse bias. In the mid-IR region, two peaks at 5 and 8.9 microm can be observed for low and high forward bias voltages,(More)