Like most commercially available QWIPs, the sensor operates by the photoexcitation of electrons between sub-bands of quantum wells fabricated by placing very thin layers of two different, high-bandgap semiconductor materials alternately on a GaAs base or template. The development of QWIPs, however, could not have emerged without a confluence of technologies.
To control the quantum-well width and the barrier height, uniformly pure semiconductor layers must be grown on large substrate wafers to a fraction of a molecular layer.
In the design of QWIP devices, absorption of IR photons excites electrons from the ground state of a quantum well to an excited state close to or within an adjacent energy-transport band. This causes a photocurrent that can be detected and further processed.
When these layers are sufficiently thin, the energy levels will show confinement; the continuous energy levels found in bulk material become discrete energy levels in these layers. In the following part of the discussion we will only consider the conduction band.
With bias voltage applied the higher level aligns to the edge of the conduction band. This structure can then act as a photon detector: This electron can freely participate in the charge transport in the conduction band.
Once the electron is in an excited state, it can escape into the continuum and be measured as photocurrent. To externally measure a photocurrent the electrons need to be extracted by applying an electric field to the quantum wells. The efficiency of this absorption and extraction process depends on several parameters. Whenever an electron is excited and extracted as photocurrent, an extra electron is injected from the opposite emitter contact to balance the loss of electrons from the quantum well.
On the other hand, this also prevents us from having a deep bound state from which the thermal excitation can be suppressed even at high temperature. Perhaps the most attractive feature of a QWIP in this respect is the fact that absorption spectrum can be tuned by quantum well thickness and the barrier composition. The development of infrared photodetectors IR was started after the Second World War, and it has since been progressing at a rapid pace. Users can incorporate the different types of noise associated with quantum wells using various noise models in the SILVACO model library. With bias voltage applied the higher level aligns to the edge of the conduction band.
In that case, yet another electron is injected from the emitter contact to balance the charge, and again heads towards the well where it might or might not get captured, and so on, until eventually an electron is captured in the well. From Wikipedia, the free encyclopedia.
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A Quantum Well Infrared Photodetector (QWIP) is an infrared photodetector, which uses electronic intersubband transitions in quantum wells to absorb photons. QWIP Technologies is the only source for bound to quasibound GaAs quantum well infrared photodetectors (QWIP) and sensors for infrared detection in military .
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