Blocked Impurity Band Detectors for Infrared Applications
Summary
Blocked impurity band (BIB) detectors represent a class of extrinsic photodetectors optimised for infrared sensing from the mid-infrared to the terahertz region. These devices employ a heavily doped semiconductor layer in which an impurity band is formed below the conduction band, stacked against an undoped blocking layer that suppresses dark current. Upon infrared illumination, electrons are photo-excited from bound impurity states into the conduction continuum and drift under an applied bias, yielding a photocurrent with high responsivity and low noise. The blocking layer prevents thermally generated carriers from reaching the contacts, thus enhancing detectivity and extending the long-wavelength cutoff beyond that of conventional photoconductive detectors. BIB architectures have been realised in materials such as silicon doped with arsenic and germanium doped with gallium or boron, and they have found application in space-borne and ground-based astronomy, environmental monitoring, medical imaging and security screening. Ongoing advances address challenges in array uniformity, quantum efficiency, operating temperature and spectral selectivity. Surface treatments, anti-reflection coatings and electrode geometry optimisation further improve photon coupling and reduce reflection losses. As infrared technology becomes integral to climate science, industrial inspection and defence, BIB detectors continue to offer a compelling combination of sensitivity, speed and spectral coverage.
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Blocked Impurity Band Detectors for Infrared Applications publication trend
The graph below shows the total number of articles in blocked impurity band detectors for infrared applications across all publications each year (not limited to Nature Index journals).
Technical terms
Blocked impurity band detector: A photodetector that combines a highly doped semiconductor layer forming an impurity band with an undoped blocking layer to suppress dark current and enhance long-wavelength response.
Impurity band: A sub-band within the semiconductor bandgap created by a high concentration of dopant atoms, facilitating sub-bandgap photon absorption.
Blocking layer: An intrinsic or lightly doped semiconductor region adjacent to the doped layer, acting as a barrier to thermally generated carriers and reducing noise.
Responsivity: The ratio of photocurrent generated to incident optical power, typically expressed in amperes per watt (A/W).
Detectivity: A figure of merit that normalises responsivity by noise, indicating the smallest detectable signal, often expressed as Jones (cm·Hz½/W).
References
- Observation of gain operation mode in Ge:B BIB THz detector. AIP Advances (2021).
- The Anti-Reflection Coating Design for the Very-Long-Wave Infrared Si-Based Blocked Impurity Band Detectors. Crystals (2022).
- Optimization of Pixel Size and Electrode Structure for Ge:Ga Terahertz Photoconductive Detectors. Sensors (2022).
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