By cascading multiple GaInAsSb active regions, the authors have fabricated 2.4μm light-emitting diodes that, for a given light output, operate at reduced current and higher voltage, which can be advantageous for battery-powered sensor applications. Tunnel heterojunctions separating emission regions add no measurable series resistance. Devices are demonstrated at room temperature with continuous wave output.

This paper describes molecular beam epitaxial growth, processing and room temperature characterization of lattice-matched GaInAsSb mid-infrared detectors on GaSb substrates for room temperature operation. For the first time, we demonstrate GaInAsSb detectors operating under backillumination, a critically important geometry for flip-chip-mounted focal plane arrays, and achieve performance equal or superior to frontilluminated detectors. Very high quantum efficiency and flat spectral response are achieved for the back-illuminated detectors due to improved carrier collection efficiency, photon recycling and reduced carrier recombination. In situ RHEED intensity oscillations and post-growth XRD are used for coarse and fine tuning of GaInAsSb lattice matching, respectively.

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A focal plane array detector sensitive from 2.0-2.5 µm and consisting of 32, 1.0 mm x 50 µm pixels, all functional, is demonstrated. Mean room-temperature R 0 A is found to be 1.0 Ω-cm 2 , limited by sidewall leakage. The focal plane array is fabricated from an MBE-grown homojunction p-i-n GaInAsSb grown on an n-type GaSb substrate. Backillumination geometry is compared to front-illumination geometry and is found to be favorable, particularly the improved responsivity (1.3 A/W at 2.35 µm corresponding to 68% quantum efficiency) due to reflection of light off the metal contact. Further, back-illumination is the most convenient geometry for mounting the array onto a compact blood glucose sensor because both contacts can be mounted on one side, while detector illumination occurs on the other.

The performances of a pin versus a pn structure from GaInAsSb materials operating at room temperature are compared both from a theoretical point of view and experimentally. Theoretically, it is found in materials limited by generationrecombination currents, pn junctions have a higher D* than pin junctions. The thinner depletion region of pn junctions results in a lower responsivity but a higher dynamic resistance, giving an overall higher D* compared to a pin structure. A series of five p+pn+ Ga 0.80 In 0.20 As 0.18 Sb 0.82 detector structures latticed matched to GaSb substrates and with 2.37 µm cut off wavelength were grown by molecular beam epitaxy and processed into variable size mesa photodiodes. Only the doping of the absorbing (p) region was varied from sample to sample, starting with nominally undoped (~1x10 16 cm -3 pbackground doping due to native defects) and increasing the doping until a p+n+ structure was attained. Room temperature dynamic resistance-area product R 0 A was measured for each sample. A simple method is presented and used to disentangle perimeter from areal leakage currents. All five samples had comparable R 0 A's. Maximum measured R 0 A was 30 Ω-cm 2 in the largest mesas. Extracted R 0 A's in the zero perimeter/area limit were about ~50 Ω-cm 2 (20-100 Ω-cm 2 ) for all samples. Within uncertainty, no clear trend was seen. Tentative explanations are proposed.