Fig. 2: Active region characterization and device reflectance under DC bias.
From: Fast amplitude modulation up to 1.5 GHz of mid-IR free-space beams at room-temperature
a Top panel: transmission through the bare active region in a typical multipass geometry, at room-temperature: a clear ISB transition at about 955 cm−1 is measured. Bottom panel: room-temperature reflectance spectra under FTIR-coupled microscope of the p = 4.2 μm sample. The black solid line is the reflectance at no bias; the green solid line corresponds to the application of +6 V. The Rabi-splitting decreases by 25%. b Optical microscope images of the large devices (left; surface 5 × 104 μm2) and of the small ones (right; surface 2 × 104 μm2). The bonding pad (BP in the figure) has the same dimensions (100 × 100 μm2)in both samples. c Modulation height extracted from the spectra of panel a (large devices). It is defined as min\(\left(\left| \frac{R{_{{\mathrm{NB}}}}-R_{{\mathrm{B}}}}{R_{{\mathrm{B}}}}\right| , \left| \frac{R_{{\mathrm{NB}}}-R_{{\mathrm{B}}}}{R_{{\mathrm{NB}}}}\right| \right)\) and it is plotted in the range 800–1100 cm−1 for both 3 V (blue solid line) and 6 V (green solid line) biases. The semi-transparent orange region corresponds to the nominal wavelength coverage of our commercial, tunable mid-IR QC laser source.
