The strong potential of intersubband detectors in the field of mid-infrared photodetection places this technology as a relevant alternative to HgCdTe detectors in the race for ultrafast operation. While their extremely short photocarrier's lifetime opens up possibilities of detection beyond 100 GHz, it is also the main reason for their comparatively high dark current. Here, a photovoltaic quantum cascade detector at 10.3 μm, embedded in a metal–metal patch antenna is presented in both direct and heterodyne detection schemes. In DC, a responsivity of 122 mA/W at 77 K and 85 mA/W at 295 K is reached. More strikingly, the device shows temperature independent heterodyne response with a capacitance-limited cutoff frequency of 25 GHz both at 77 K and room temperature. It is modeled quantitatively by means of an equivalent RC-circuit picture stemming from microscopic transport considerations.
We revisit the Fabry–Perot (FP) reflectivity method to measure optical indices in the mid-infrared spectrum. This simple approach can be readily implemented using a standard Fourier transform infrared spectrometer. Measuring samples with multiple heights allows for enhanced precision of the measurement, making the FP method consistent in values and uncertainties with more advanced ellipsometric measurements. An extensive discussion about experimental errors is carried out. Results between 4 and 12 µm for AlInAs, n-doped InGaAs, and InP, which are the most standard materials for quantum cascade lasers, are given.
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