We discuss state-of-the-art mid-infrared light emitters and detectors based on the so-called 6.1 Å family of semiconductors, i.e. InAs, GaSb, and AlSb. Via epitaxial design routines, heterostructures composed of their binary, ternary or quaternary alloys allow unique features such as optically active type-II superlattices enabling light emitters and detectors suitable for the mid-infrared wavelength region. Here we compare and discuss the design differences between interband cascade infrared detectors employing Ga free Type II superlattices and resonant tunneling diodes (RTD) employing the quaternary alloy GaInAsSb. We show that by substituting the standard InAs/GaSb superlattice for a Ga-free superlattice, i.e. InAs/InAsSb, one requires an inverted carrier extraction path. Here it is needed to form a hole-ladder in the electron-barrier, instead of an electron-ladder in the hole-barrier. At elevated temperatures, we observe seven negative-differential-conductance (NDC) regions due to electrons tunnelling through the electron barriers of the seven cascade stages. The detector operates in photovoltaic mode with a cut-off wavelength of 8.5 μm. The RTD photodetector on the other hand utilizes GaInAsSb absorbers that allow efficient operation in the 2-4 μm range with significant electrical responsivity of 0.97 A/W at 2 μm. Contrary to interband cascade infrared detectors, RTD PD operate only at finite voltages and hence these devices are Shot noise limited.

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