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The strong potential of intersubband detectors in the field of mid-infrared photodetection places this technology as a relevant alternative to HgCdTe detectors in the race for ultrafast operation. While their extremely short photocarrier's lifetime opens up possibilities of detection beyond 100 GHz, it is also the main reason for their comparatively high dark current. Here, a photovoltaic quantum cascade detector at 10.3 μm, embedded in a metal–metal patch antenna is presented in both direct and heterodyne detection schemes. In DC, a responsivity of 122 mA/W at 77 K and 85 mA/W at 295 K is reached. More strikingly, the device shows temperature independent heterodyne response with a capacitance-limited cutoff frequency of 25 GHz both at 77 K and room temperature. It is modeled quantitatively by means of an equivalent RC-circuit picture stemming from microscopic transport considerations. [ABSTRACT FROM AUTHOR]

We demonstrate terahertz intersubband absorptions in nitride step quantum wells (SQWs) grown by metal organic vapor phase epitaxy simultaneously on two different substrate orientations [Si(111) and Si(110)]. The structure of the SQWs consists of a 3 nm thick Al0.1Ga0.9N barrier, a 3 nm thick GaN well, and an Al0.05Ga0.95N step barrier with various thicknesses. This structure design has been optimized to approach a flatband potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moment. Structural characterizations prove the high quality of the samples. Intersubband absorptions at frequencies of 5.6 THz (λ ≈ 54 μm), 7 THz (43 μm), and 8.9 THz (34 μm) are observed at 77 K on both substrate orientations. The observed absorption frequencies are in excellent agreement with calculations accounting for the depolarization shift induced by the electron concentration in the wells. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Tunneling transport in a quantum cascade detector is investigated. With regard to coherent transport in quantum cascade lasers, a Kazarinov–Suris approach R. F. Kazarinov and R. A. Suris, [Sov. Phys. Semicond. 6, 120 (1972)] needs to be modified through the introduction of an additional Fermi–Dirac factor in order to properly model the experimental data at low temperature. Electronic current is completely dominated by tunneling transport; the model here presented should help to suppress it in the future design of efficient quantum cascade detectors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We demonstrate high thermal dissipation of quantum cascade lasers (QCLs) using multi-stripes array technology. Buried QCL arrays offer both lateral dissipation enhancements while keeping beam quality control for large active region lasers. Experimental thermal resistances down to 2 K/W are reported. InP:Fe regrowth morphology has been optimized to limit current leakage. Thermal resistance decreasing with both number and width of emitters is demonstrated. Comparison with simulation shows excellent agreement, with a reduction factor of 3 when comparing to standard ridges QCL. These low thermal resistances project up to 40 W in continuous wave operation using state-of-the-art QCL design. [ABSTRACT FROM AUTHOR]

Electronic transport in intersubband detectors is investigated theoretically and experimentally. Within the framework of inter-Wannier-Stark levels electron scattering, consistent dark current and low-frequency noise expressions are obtained through the resolution of the two first moments of a master equation for classical particles. In particular, the formulation of noise bridges over the vision of uncorrelated Johnson and shot contributions. Theoretical predictions are compared to measurements for five quantum well detectors, either photovoltaic or photoconductive, whose detection wavelength span from 8 &b.mu;m to 17 &b.mu;m. Quantitative agreement with experiment is found for a broad range of biases and temperatures. Correlation effects are discussed and proven to either reduce or enhance the noise. [ABSTRACT FROM AUTHOR]