BLANC - Blanc

Optimisation du Transport Electronique dans les Détecteurs à Cascade Quantique – OTEQ

Submission summary

Middle Infrared detection is developed for the applications of night vision or thermal imaging in general. Applications include fire fighting, medical or military applications. Figure 1 is a picture of a thermal image obtained with an infrared focal plane array. We can see a glas with hot liquid in it (in white) together with another cold glas. We can also see the heat of the hand which was touching the table just a second before, as a signature of thermal imaging. In France, thermal imagers are developed by Thales, Sagem, Cedip, ULIS or Sofradir. Other companies are developing these imagers in Germany, Sweden, United Kingdom, Israel, and of course, a lot in the United States (Rockwell, Raytheon, FLIR...). The development of these cameras include the study of new focal plane arrays, with new materials or new semiconductor heterostructures, which needs semiconductor engineering and physics. For this, collaborations between industrial partners and academic laboratories are welcome. In France, the LETI in Grenoble, ONERA in Palaiseau or the University of Paris 7, in collaboration with Alcatel Thales 3-5 lab, are some examples of this kind of collaboration. - - There are two kinds of detectors : low cost, room temperature detectors (uncooled detectors), with intermediate performances on the one side, and very high performance semiconductor cooled detectors on the other. The latter are of course more expensive. Among these high performance detectors, different materials can be used : InSb, HgCdTe, GaAs/AlGaAs quantum wells, are the most wellknown. - - Quantum well infrared photodetectors (QWIPs) have been developed in the past ten years from the fundamental-physics point of view towards fabrication of large area focal plane arrays. In a standard QWIP, an electric field is applied to the multiple quantum well (QW) heterostructure in order to photo-ionize the quantum wells and collect the photocurrent. In this photoconductive mode, a typical electric field of a few tens of kV/cm is applied on the structure. This electric field results in a significant dark current, which saturates the capacitance of the read-out circuit in large focal plane arrays. As a consequence, the typical integration time is usually shorter than the video frame time. - - For that reason, low dark-current structures with a good quantum efficiency are developped. Very recently, we proposed a new structure designed as a quantum cascade photodetector (QCD). This structure works without any applied bias in a photovoltaic mode, and therefore has no dark current. QCDs appear very promising for small-pixel, large-area focal plane arrays. - - In a quantum cascade structure, there is no applied electric field. Thanks to a photon, an electron goes from the fundamental level of the structure to the excited state and then is transferred thanks to relaxation through a cascade of levels, to the next period. In such a structure, there is no dark current (no applied bias). - - The quantum structure is designed to generate an electronic displacement through a cascade of quantum levels when the device is illuminated and this without applying any bias voltage. The main objective is to suppress dark current existing in photoconductive detectors and limiting the operating temperature. The physics of the electronic transport in QCDs needs to be fully understood in order to design high performance infrared detectors. The problem of the transport in complex semiconductor heterostructures is related to other studies in chemistry : How does the current go through complex molecules like polymers ? This is the general problem of 1D mesoscopic currents in complex quantum structures. - - The objective of this project is to understand the physics of the transport in quantum cascade structures, thanks to experiments under magnetic field, which enable to extract transfer times between quantum levels and finally fully model the I(V) characteristics. The objective is to obtain for the first time a...

Project coordination

Vincent BERGER (Université)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 230,000 euros
Beginning and duration of the scientific project: - 36 Months

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