L. Doyennette

Quantum cascade detectors for very long wave infrared detection

A high responsivity GaAs/AlGaAs quantum cascade detector is demonstrated at a wavelength of 15 μm. The quantum design is optimized for negative bias operation, so that the capture of photoexcited electrons back to the fundamental level is minimized. The detectivity of the detector presented here reaches 1.1×1012 Jones at 25 K for an applied bias of −0.6 V.

Space charge mediated negative differential resistance in terahertz quantum well detectors

In terahertz quantum well infrared photodetectors, a built-in-charge-mediated regime transition of the electronic transport is thoroughly investigated. The very strong current discontinuity and negative differential resistivity behavior are explained in terms of band structure reorganizations. The analysis of bias versus current measurements reveals that the transition occurs when the first two wells of the structure become partially drained, and the second well enters the ionized regime before the first one. Both many-body effects and a careful model of the contact have to be considered to account for these features. The source of the built-in charge is identified as intersubband impact ionization. The regime transition is one of its few experimental proofs, and provides an original approach to investigate hot electron kinetics in multi-quantum-well structures.

State of the art of quantum cascade photodetectors

The Quantum Cascade Detector (QCD) is a multiple quantum well photodetector working at low bias or zero bias. It has a zero dark current occurring at 0V, together with a high photovoltaic photoresponse, since the QCD does not need any applied field to improve the collection of electrons. QCDs have been tested at various wavelengths, from short wavelengths (1.5 microns) up to THz waves, through the entire infrared spectrum (middle and long wavelengths). Theory of transport in QCD is now well established, and leads to accurate calculations of current and noise in QCDs, with a very good agreement with experimental results. Latest results and state of the art of performances of QCDs are presented.

Johnson and shot noises in intersubband detectors

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.

Predictive circuit model for noise in quantum cascade detectors

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.

Long range resonant tunneling in quantum cascade structures

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.

Magnetotransport in quantum cascade detectors: analyzing the current under illumination.

Photocurrent measurements have been performed on a quantum cascade detector structure under strong magnetic field applied parallel to the growth axis. The photocurrent shows oscillations as a function of B. In order to describe that behavior, we have developed a rate equation model. The interpretation of the experimental data supports the idea that an elastic scattering contribution plays a central role in the behavior of those structures. We present a calculation of electron lifetime versus magnetic field which suggests that impurities scattering in the active region is the limiting factor. These experiments lead to a better understanding of these complex structures and give key parameters to optimize them further.

Magnetotransport in very long wave infrared quantum cascade detectors: Analyzing the current with and without illumination

Current measurements of current have been performed on a very long wave infrared quantum cascade detector under magnetic field under both dark and light conditions. The analysis of dark current as a function of temperature highlights three regimes of transport. Under illumination, the model developed is in agreement with the oscillatory component of the experimental magnetophotocurrent. It allows to identify the key points controlling the electronic transport: crucial role of extraction, location of ionized impurities and scattering mechanisms involved in the structure. This work is valuable for the future conception of high-performance quantum cascade detectors in the infrared range.

Description of transport mechanisms in a very long wave infrared quantum cascade detector under strong magnetic field

Measurements of current have been performed on a very long wave infrared quantum cascade detector under strong magnetic field applied parallel to the growth axis, both under dark and light conditions. The analysis of dark current as a function of temperature highlights three regimes of transport involving the different energy levels of the structure. For photocurrent analysis, we developed a model based on a rate equation approach taking into account all the electronic levels of the structure. This model is in agreement with the oscillatory component of the experimental magnetophotocurrent. It allows to identify the key points controlling the electronic transport such as extraction from the upper level of the optically active quantum well, location of ionized impurities, and scattering mechanisms involved in the structure. This work is valuable for the future conception of high-performance quantum cascade detectors in infrared and far infrared range.

Impact ionization in THz QWIPs

Recently phase transitions in THz Quantum Wells Inter-subband Photodetectors (QWIP) were observed. Very large current discontinuities - up to five orders of magnitude - were obtained, at low temperature [1]. Quantum well impact ionization shifts the structure from a resistive “down” state, where the current flows through inter-well quantum tunneling to a highly conductive “up” state. In this paper, thanks to the analysis of the bias versus current “s” curve, an accurate investigation of impact ionization processes in quantum wells is analyzed. The use of these phenomena for high sensitivity quantum well THz detection will be presented.