The increasing demand of rapid sensing and diagnosis in remote areas requires the development of compact and cost-effective mid-infrared sensing devices. So far, all miniaturization concepts have been demonstrated with discrete optical components. Here we present a monolithically integrated sensor based on mid-infrared absorption spectroscopy. A bi-functional quantum cascade laser/detector is used, where, by changing the applied bias, the device switches between laser and detector operation. The interaction with chemicals in a liquid is resolved via a dielectric-loaded surface plasmon polariton waveguide. The thin dielectric layer enhances the confinement and enables efficient end-fire coupling from and to the laser and detector. The unamplified detector signal shows a slope of 1.8–7 μV per p.p.m., which demonstrates the capability to reach p.p.m. accuracy over a wide range of concentrations (0–60%). Without any hybrid integration or subwavelength patterning, our approach allows a straightforward and cost-saving fabrication.

We demonstrate a bi-functional quantum cascade device that detects at the same wavelength as it coherently emits. Our fabricated device operates at room-temperature with a pulsed peak power emission of 45 mW and a detector responsivity of 3.6 mA/W. We show how to compensate the intrinsic wavelength mismatch between the laser and the detector, based on a bound-to-continuum design. An overlap between the laser and the detector spectra was observed from 6.4 lm to 6.8 lm. The electro-luminescence spectrum almost perfectly matches the detector spectrum, overlapping from 6.2 lm to 7.1 lm. V

We demonstrate the concept of diagonal transitions for quantum cascade detectors (QCD). Different to standard, vertical QCDs, here the active transition takes place between two energy levels in adjacent wells. Such a scheme has versatile advantages. Diagonal transitions generally yield a higher extraction efficiency and a higher resistance than vertical transitions. This leads to an improved overall performance, although the absorption strength of the active transition is smaller. Since the extraction is not based on resonant tunneling, the design is more robust, with respect to deviations from the nominal structure. In a first approach, a peak responsivity of 16.9 mA/W could be achieved, which is an improvement to the highest shown responsivity of a QCD for a wavelength of 8 μm at room-temperature by almost an order of magnitude.

We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.

In this letter, we introduce the InAs/AlAsSb material system for quantum cascade detectors (QCDs). InAs/AlAsSb can be grown lattice matched to InAs and exhibits a conduction band offset of approximately 2.1 eV, enabling the design of very short wavelength quantum cascade detectors. Another benefit using this material system is the low effective mass of the well material that improves the total absorption of the detector and decreases the intersubband scattering rates, which increases the device resistance and thus enhances the noise behavior. We have designed, grown, and measured a QCD that detects at a wavelength of λ = 4.84 μm and shows a peak specific detectivity of approximately 2.7 × 107 Jones at T = 300 K.