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.