LED-photodiode opto-pairs

Abstract

We have demonstrated that InAs-based narrow gap heterostructures exhibit a potential barrier at the p-n junction up to 300°C and are able to operate in positive and negative luminescence modes in the 3-5 μm spectral range: the latter being preferable for elevated temperatures in terms of the output power. The optimization of mid-IR diode construction by implementing rare earth gettering, and the use of a broad mirror anode contact and graded bandgap or heavily doped "windows" has lead to "universal" flip-chip devices that are able to operate as efficient LEDs with Fabry-Perot resonant features with an output as high as ∼0.5 mW/A and as photodiodes with a detectivity as high as 2×1010 cm Hz1/2 W-1. Optical pumping using a GaAs LED appears to be an efficient way of realizing an InAsSb emitter with a conversion efficiency ∼10 μW/A in the 8 μm spectral region. The coupling of the flip-chip devices with immersion lenses or fibres through the use of high index chalcogenide glass together with an appropriate choice of the bias direction at the p-n junction can yield an additional performance enhancement of a factor of 3-5. Optically coupled LED-PD pairs can be used as precise low voltage or current sensors of gases and liquids, e.g. with an expected limit of detection for methane gas as small as LODΔf=1MHz =18 ppm·cm·mA· s1/2. © 2006 Springer-Verlag London Limited.