Quantum well infrared photodetector
A quantum well infrared photodetector ( English quantum well infrared photodetector , QWIP detector for short ) is a semiconductor detector for the detection of infrared radiation, especially in the range 8 ... 14 µm. Alternating thin layers (typically around 50) made of III-V semiconductors (e.g. AlGaAs / GaAs ) with different band gaps form quantum wells that absorb infrared radiation and release charge carriers.
properties
They are operated cooled. Temperatures below 77 K, the boiling point of nitrogen, are common . Nowadays the cooling is accomplished with Stirling engines instead of liquid nitrogen.
QWIPs have some advantages and disadvantages compared to the HgCdTe photodiodes used in comparable applications :
Advantages:
- lower dark current
- shorter service life of thermally excited charge carriers
- narrow-band spectral sensitivity
Disadvantage:
- Radiation must not arrive perpendicular to the sequence of layers (no absorption)
- Quantum yield lower (10%) than with HgCdTe photodiodes (> 70%)
They are predestined for so-called focal plane arrays (camera chips) in the mid-infrared (around 10 µm wavelength). Long integration times are possible due to the low dark current. Using different reception wavelengths (several chips), high-resolution “colors” can be distinguished.
The properties result in the following applications:
- Atmospheric research
- Space exploration
- Thermography in science and technology as well as in the military
Camera chips consist of the quantum well structure plate, which is two-dimensionally contacted with a readout integrated circuit (ROIC ) based on silicon, pixel by pixel.
Cameras with QWIP arrays with 640 × 512 pixels and high pixel uniformity can be manufactured inexpensively. Noise-equivalent temperature differences of less than 10 mK can be achieved.
Sources and literature
- ^ A. Rogalski: Quantum well photoconductors in infrared detector technology. In: Journal of Applied Physics , Volume 93, Issue 8, April 15, 2003; Page 9 in the pdf, Page 4362 in the year, accessed on June 27, 2017 (PDF; 1.7 MB; English)
- ↑ Jie Zhang, Win-Ching Hung: Quantum Well Infrared Detector. University of Rochester , Department of Electrical and Computer Engineering (ECE), accessed June 27, 2017 (Power Point presentation)
- ^ John Wallace: Photonics Products: MWIR and LWIR Detectors: QWIPs capture LWIR images at low cost. In: Laser Focus World , October 7, 2015, accessed June 27, 2017