Abstract
The design, fabrication, and characterization of a resonant cavity-enhanced photodetector (RCE PD) operating in the long-wavelength infrared regime are demonstrated. The incorporation of the low bandgap InAs/InAs0.70Sb0.30 type-II strained-layer superlattice into the absorber layer of the detector cavity, along with the high-reflectivity (Rm > 0.9) AlAs0.08Sb0.92/GaSb distributed Bragg reflector pairs, results in resonant enhancement at 7.7–7.8 μm, which is a spectral region relevant in applications in sensing of chemical warfare agents and in medical biomarker diagnostics. These resonant wavelength peaks also display a high quality factor in the range of 76–86 and a small temperature coefficient of 0.52 nm K−1. An nBn architecture, where an Al0.71Ga0.29As0.08Sb0.92 layer acts as a barrier for majority electrons while minimizing the valence band offset with the absorber, is also incorporated into the cavity in order to improve the electrical properties of the detector. Spectral response measurements yield a peak external quantum efficiency of 14.6% and a peak responsivity of 0.91 A W−1 at 77 K and −0.8 V; meanwhile, a dark current density of 2.0 × 10−4 A cm−2 at 77 K results in a specific detectivity of 3.7 × 1010 cm Hz1/2 W−1, coming close to the theoretical background-limited D* of an ideal broadband photovoltaic detector with the superlattice composition as that of the RCE PD.
Highlights
AlGaAs/GaAs being a popular choice for the distributed Bragg reflectors (DBRs) mirrors,5 and the use of InGaAs absorbers extending the resonant range to 1.55 lm.6 To make absorption possible in the MWIR regime, other material systems were necessary
An resonant cavity-enhanced photodetector (RCE PD) that functions in the long-wavelength infrared (LWIR) regime is demonstrated as a proof of concept
Scitation.org/journal/apl particular interest for security applications, as it includes absorption fingerprints from a number of gases and chemicals commonly found in explosives, such as pentaerythritol tetranitrate (PETN) ($7.8 lm),11 acetic acid (7.2 and 7.8 lm),11 cyclonite and TNT,12 and a number of other compounds,13 and where development of spectrally selective detectors could help the realization of stand-off threat detection systems, which currently rely on broadband detection
Summary
AlGaAs/GaAs being a popular choice for the DBR mirrors,5 and the use of InGaAs absorbers extending the resonant range to 1.55 lm.6 To make absorption possible in the MWIR regime, other material systems were necessary. Further analysis of the Arrhenius plot reveals an activation energy (Ea), which decreases monotonically with increasing voltage from 78 meV at À0.1 V to 38 meV at À1 V in all temperature regions, fitted for the high-doped regime.25 by analyzing the cut-off wavelength of the broadband reference nBn device, the lowtemperature bandgap of the absorber is found to be $135 meV.
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