Recently developed narrow band (FWHM ~ 0.1* l max) mid-infrared III-V
LEDs can emit with peak wavelengths up to 5.5 mm and can,
therefore, be used to replace thermal sources and rotating chopper wheels in the design of
new spectroscopic CnHm (3.3 mm), CO2
(4.3 mm), CO (4.7 mm) and
NO (5.3 mm) gas analyzers. At present several analyzers with
sensors containing LED and lead salt photoresistors are graduating from research to
development stage. However, slow photoresistor response, high noise and operating voltage
as well as instability against temperature cycling do not allow to design portable
instruments for measuring within the ppm region at room and higher temperatures.
Photodiode-LED pairs operating at low or zero detector bias are, therefore, a good
challenge for the above applications.
The developing 3.4-3.8 µm spectral range was the
most successful area of our recent activity. Creating back-side illuminating
(flip-chip bonding) LEDs and PDs (2000 y.) with record parameters and
successful interfacing them with immersion lens (2001 y.) leads to the
up to 100 dB signal/noise optopair ratio (see fig.: S/N ratio -
left scale, LED power consumption - right scale).
-
- See also:
-
