Introduction to Infrared Detectors and Quantum Dots

The majority of objects, those with a temperature between 100 and 400 K, emit strong electromagnetic radiation in the infrared region, especially in 1–14 µm region, which includes short-wavelength infrared (SWIR, ~1.0–3.0 µm), medium-wavelength infrared (MWIR, ~3.0–5.0 µm), long-wavelength infrared (LWIR, ~8.0–14.0 µm) and some part of very-long infrared (VLWIR, ~14.0–100.0 µm). MWIR and LWIR detectors are widely used today in a variety of imaging and video-graphic applications, in fields such as spectroscopy, night vision, thermal imaging, health science, and space research and defence. Different types of IR detectors are based on various semiconductor materials, such as Si, InAs1−x Sb x , Pb1−x Sn x Te, and Hg1−x Cd x Te. To overcome limitations in extending the detection wavelength in longer wavelength region the idea of intersubband transition based photodetectors has been introduced. The spacing between different electronics subbands (a few tenths to hundreds of meV) allows emission or detection of a broad range of IR radiation. Quantum mechanical properties dictate that if any material is scaled down to very small dimension both the conduction and valence band can be split into a number of intersubband energy levels. The dimension of the bulk can be reduced to form different nanostructures, such as quantum wells (QWs), quantum wires and quantum dots (QDs). QDs confine the carriers in all three directions, which results in a complete delta-like DOS in the different energy levels. In recent past MBE grown III–V semiconductors based quantum dots infrared photodectors (QDIPs) have emerged as a potential candidate in the field of MWIR and LWIR imaging technology. Their 3-D carrier confinement provides intrinsic sensitivity to normal incidence radiation, lower dark current and a long excited-state lifetime compared to quantum well infrared photodetectors (QWIPs).