Quantum well infrared photodetector

A Quantum Well Infrared Photodetector (QWIP) is an infrared photodetector, which uses electronic intersubband transitions in quantum wells to absorb photons.

QWIPs are typically made of gallium arsenide, a material commonly found in smartphones and high-speed communications equipment.

[1] Depending on the material and the design of the quantum wells, the energy levels of the QWIP can be tailored to absorb radiation in the infrared region from 3 to 20 μm.

[2] QWIPs are one of the simplest quantum mechanical device structures that can detect mid-wavelength and long-wavelength infrared radiation.

[3] In 1985, Stephen Eglash and Lawrence West observed strong intersubband transition in multiple quantum wells (MQW) that prompted more serious consideration into using quantum wells for infrared detectors.

In 1990, the low-temperature sensitivity of the technology was further improved by increasing the barrier thickness, which suppressed the tunneling current.

[5] At this point, these devices were formally known as quantum well infrared photodetectors.

The instrument exhibited a peak detection wavelength of 7.5 micrometers for positive bias at 10 K when the electrons resided in one of the quantum wells and switched to 8.8 micrometers at a large negative bias when the electrons were transferred to the other well.

At the time, the photodetectors could only sense the one-dimensional quantization when the light traveled in parallel to the material layers, which typically occurred when light was shined at the edge of the detector.

In addition, the reflection gratings commonly used in the industry to alleviate this problem were made of very fine periodic posts and were difficult to produce in large formats.

[1] To address this problem, researchers at the Army Research Laboratory developed the corrugated quantum infrared photodetector (C-QWIP) in 2008, which used micromirrors on the photodetector to increase the effectiveness of redirecting the light onto the quantum well region at any wavelength.

[9] In essence, the 45-degree inclined detector sidewalls allowed light to be reflected parallel to the material layers to produce an electrical signal.

[10] Tests conducted by researchers at ARL and L-3 Communications Cincinnati Electronics determined that the C-QWIP demonstrated bandwidths exceeding 3 micrometers, which was 5 times wider than the commercial QWIP at the time.

[9] Since C-QWIPs can be manufactured using gallium arsenide, they served as a more affordable alternative to conventional infrared detectors for Army helicopters without sacrificing resolution and requiring less calibration and maintenance.

[11] In February 2013, NASA launched a satellite that featured the Thermal Infrared Sensor (TIRS) instrument as part of its Landsat Data Continuity Mission.

The TIRS utilized three C-QWIPs designed by the Army Research Laboratory to detect long wavelengths of light emitted by the Earth and track how the planet's water and land are being used.

[1][11][12] Infrared detectors generally work by detecting the radiation emitted by an object, and the intensity of the radiation is determined by factors such as the object's temperature, distance, and size.

As a result, it can be used to detect objects with much lower energy radiation than what was previously possible.

[5] The basic elements of a QWIP are quantum wells, which are separated by barriers.

When a bias voltage is applied to the QWIP, the entire conduction band is tilted.

Without light the electrons in the quantum wells just sit in the ground state.

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.

are the probabilities for a photon to add an electron to the photocurrent, also called quantum efficiency.

, so an injected electron might sometimes pass over the quantum well and into the opposite contact.

The number of quantum wells appears only in the denominator, as it increases the capture probability