A large-scale quantum dot IR focal plane array

Abstract

Potential uses for light detectors operating in the 8–15μmwavelength range include groundand space-based applications such as night vision, temperature detection, early warning systems, navigation, flight control systems, weather monitoring, as well as security and surveillance. In addition, they can be used to monitor and measure pollution, relative humidity profiles, and the distribution of different gases (such as ozone, carbonmonoxide, and nitrous oxide) in the atmosphere. This is due to the fact that most of the absorption lines of gas molecules lie in this IR spectral region. The earth’s atmosphere is opaque to most of the IR. Of its few transparent windows, the 8–12μm is one of the clearest. Cameras operating in this wavelength range and used in ground-based telescopeswill be able to see through the earth’s atmosphere, image distant stars and galaxies, and help in the search for cold objects such as planets orbiting nearby stars. Traditional quantum well IR photodetectors are made from a combination of group III and group V elements and already offer extremely high operability, mature fabrication technology, very large formats, and material production that is increasingly high volume and low cost. However, operating temperatures are moderate (40–80K), and efficiency is limited. Past attempts at solving these issues focused on improving materials quality and designing new devices. In this work we exploited the artificial atomlike properties of self-assembling quantum dots (QDs) to developmore efficient large-scale (640×512 pixel) highoperating-temperature long-wavelength infrared (LWIR) focal plane arrays (FPAs) without sacrificing the economic advantages of the mature III-V IR imaging system pipeline. QDs are nanometer-scale islands that form spontaneously on a semiconductor substrate due to lattice mismatch. QDs can confine the carriers (i.e., electrons or holes) in 3D, modifying the optical transition selection rule that forbids a quantum well from absorbing normal incident radiation and enhancing quantum efficiency. The 3D confinement of the photoexcited carrier by a quantum dot IR photodetector (QDIP) also increases its lifetime Figure 1. An image taken with the first 640×512 pixel QDIP LWIR FPA operating at 60K.