There has been an increased interest in ambient operating
mid-infrared (3.0-5.5 mm) light emitting diodes (LEDs) and diode lasers as an
alternative to thermal sources and rotating chopper wheels in the design of new
spectroscopic analyzers since most industrial gases have characteristic absorption bands
in the above spectral range (see fig.).
Optical sensors incorporating mid-IR photodiode-LED
optopair are of particular interest for low power/voltage applications such as personal
analyzers or open path leakage detectors of explosive hydrocarbons (3.3
mm) found e.g. at
petroleum plants. It is believed that III-V compounds and heterostructures are promising
materials for the above applications due to their high thermal conductivity and
metallurgical stability. In addition the In(Ga)As and InAs(Sb) based LEDs are able to
operate at temperatures as high as 130-180oC with no dramatic degradation of
power over the working period of several hundred hours.
