ABSTRACT
We report a resonant cavity infrared detector (RCID) with an InAsSb/InAs superlattice absorber with a thickness of only ≈ 100â nm, a 33-period GaAs/Al0.92Ga0.08As distributed Bragg reflector bottom mirror, and a Ge/SiO2/Ge top mirror. At a low bias voltage of 150â mV, the external quantum efficiency (EQE) reaches 58% at the resonance wavelength λres ≈ 4.6â µm, with linewidth δλ = 19-27â nm. The thermal background current for a realistic system scenario with f/4 optic that views a 300â K scene is estimated by integrating the photocurrent generated by background spanning the entire mid-IR spectral band (3-5â µm). The resulting specific detectivity is a factor of 3 lower than for a state-of-the-art broadband HgCdTe device at 300â K, where dark current dominates the noise. However, at 125â K where the suppression of background noise becomes critical, the estimated specific detectivity D* of 5.5 × 1012â cm Hz½/W is more than 3× higher. This occurs despite a non-optimal absorber cut-off that causes the EQE to decrease rapidly with decreasing temperature, e.g., to 33% at 125â K. The present RCID's advantage over the broadband device depends critically on its low EQE at non-resonance wavelengths: ≤ 1% in the range 3.9-5.5â µm. Simulations using NRL MULTIBANDS indicate that impact ionization in the bottom contact and absorber layers dominates the dark current at near ambient temperatures. We expect future design modifications to substantially enhance D* throughout the investigated temperature range of 100-300â K.
ABSTRACT
Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 µm-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M2 < 1.2 up to 1 W for â¼5 µm-wide ridges. 5 µm-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of â¼1.25 cm over a distance of 100 m.