Perspective on III–V barrier detectors

In a photodiode made from a narrow bandgap III–V material such as InSb, the dark current is usually dominated by thermal generation-recombination (GR) in the depletion region. In an XBn or XBp barrier detector, the GR current is suppressed by confining the depletion region to a wide bandgap barrier material with a band alignment that blocks majority carriers. Diffusion limited barrier detectors are essentially unipolar and represent a device architecture with unity gain that is fundamentally different from that of the traditional photodiode. High performance barrier detector arrays spanning the mid- and long-wave infrared atmospheric transparency windows are currently being produced with both bulk alloy and type II superlattice (T2SL) absorbers several micrometers thick. In T2SLs, 5–10 μm diffusion lengths have been demonstrated for both InAs/GaSb XBp and InAs/InAsSb XBn devices. The former exhibit minority electrons with a short lifetime and a high mobility, while the latter exhibit minority holes with a long lifetime and a low mobility. The contrasting behavior is understood in terms of competing GR and Auger recombination mechanisms, and a transition between metallic and nonmetallic conduction. These properties present unique challenges for the future design of monolithic dual band photodetectors.