Time-resolved photoluminescence (TRPL) spectroscopy is used to study the minority-carrier lifetime in mid-wavelength infrared, n-type, InAs/Ga 1Àx In x Sb type II superlattices (T2SLs) and investigate the recombination mechanisms and trap states that currently limit their performance. Observation of multiple exponential decays in the intensity-dependent TRPL data indicates trap saturation due to the filling then emptying of trap states and different Shockley-Read-Hall (SRH) lifetimes for minority and majority carriers, with s maj (s n0 ) ) s min (s p0 ). Simulation of the photoluminescence transient captures the qualitative behavior of the TRPL data as a function of temperature and excess carrier density. A trap state native to Ga 1Àx In x Sb is identified from the low-injection temperature-dependent TRPL data and found to be located below the intrinsic Fermi level of the superlattice, approximately 60 ± 15 meV above the valence-band maximum. Low-temperature TRPL data show a variation of the minority-carrier SRH lifetime, s p0 , over a set of InAs/Ga 1Àx In x Sb T2SLs, where s p0 increases as x is varied from 0.04 to 0.065 and the relative layer thickness of Ga 1Àx In x Sb is increased by 31%.

We demonstrate up to 39% resonant enhancement of the quantum efficiency (QE) of a low dark current nBn midwave infrared photodetector with a 0.5 μm InAsSb absorber layer. The enhancement was achieved by using a 1D plasmonic grating to couple incident light into plasmon modes propagating in the plane of the device. The plasmonic grating is composed of stripes of deposited amorphous germanium overlaid with gold. Devices with and without gratings were processed side-by-side for comparison of their QEs and dark currents. The peak external QE for a grating device was 29% compared to 22% for a mirror device when the illumination was polarized perpendicularly to the grating lines. Additional experiments determined the grating coupling efficiency by measuring the reflectance of analogous gratings deposited on bare GaSb substrates.

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A five-stage interband cascade laser with 12μm ridge width and Au electroplating for improved epitaxial-side-up heat sinking operates cw to a maximum temperature of 257K, where the emission wavelength is 3.7μm. The device emits 100mW̸facet for cw operation at 80K, 54mW at 200K, and 10mW at 250K. The beam quality is within twice the diffraction limit for injection currents up to 14 times the lasing threshold at 120K.