InAs/GaSb Type-II Superlattice for Radiation Thermometry

We report the evaluation of an InAs/GaSb type-II superlattice (T2SL) as a potential uncooled or thermo-electrically cooled midwave infrared photodiode for use in radiation thermometry. A T2SL structure was grown and analyzed. Temperature-dependent radiation thermometry measurements were performed at reference blackbody temperatures of 25 °C-100 °C, in terms of photocurrent, signal-to-noise ratio (SNR), and temperature error. Despite using an unoptimized T2SL diode, we found that an SNR >1 was obtained using an uncooled diode, even at a target temperature of 25 °C. Cooling increased the photocurrent and reduced the dark current, leading to increased SNR across the blackbody temperature range measured. For instance at a target temperature of 50 °C, cooling the diode to 77 K increases the SNR by a factor of 614, while a more modest SNR enhancement factor of 19 was obtained when the diode was cooled to 200 K. At the thermo-electric cooler compatible temperature of 200 K, a target temperature of 50 °C with a temperature error of ±1 °C could be successfully measured, demonstrating the potential of T2SL.