Noncooled InAs photodiodes for optoelectonic sensors of methane

Modern optoelectronic gaseous sensors require high performance photodetectors for mid-wavelength infrared (IR) region because of the most intensive absorption lines of carbons, which are the structural units of pollutant gases, fall into the wavelength region 3.2-3.4 /spl mu/m. The most effective sources of IR radiation in this spectral region are LEDs made of p-n-InGaAs/n-InAs and p-n-InAsSbP/n-InAs heterostructures. To be successfully used in optoelectronic gaseous sensors IR photodiodes should exhibit high sensitivity and operating speed. In many cases these photodiodes should be also explosion proof. The carrier transport mechanisms were investigated in the temperature range 77-330 K. At actual temperatures T=260-300 K the forward current is determined by two mechanisms: diffusion in the bulk and generation in the depletion region. In photodiodes with p-n junction depth h=6/spl divide/7 /spl mu/m the photoresponse spectra has maximum at /spl lambda//sub max/=3.3/spl divide/3.5 /spl mu/m (T=295 K). These dependencies are well coincide with LEDs spectra /spl lambda/=3.3 /spl mu/m. In investigated photodiodes the current responsivity was ranged from 0.7 to 0.8 A/spl times/W/sup -1/ at the wavelength 3.3 /spl mu/m. The specific detectivity D/sub /spl lambda// (3.3 /spl mu/m, 800 Hz, 1 Hz) was found to be in the range 3.0/spl divide/ 3.5/spl times/10/sup 9/ W/sup -1/ cm Hz/sup 1/2/ at T=295 K. These threshold parameters exceed analogous ones in commercially available photodiodes.