Infrared Detectors for Radiation Thermometry

This work presents an investigation into the potential next generation of infrared detectors for radiation thermometry. Motivations for this work include increased detector sensitivity, development of minimally cooled mid-wave infrared (MWIR) arrays and longer wavelength multi-colour ratio radiation thermometers.

The high sensitivity of the Si avalanche photodiode (APD) is highly attractive for radiation thermometry. A Si APD is shown to offer increased sensitivity by measuring a lower temperature than a Si photodiode in order to satisfy specific threshold voltages. The Si APD is also shown to offer improvement in the signal-to-noise ratio (SNR) and temperature error. By combining the Si APD with a phase sensitive detection (PSD) method, further improvement is achieved.

The MWIR InAs/GaSb type-II superlattice (T2SL) offers the potential development of minimally cooled MWIR arrays for radiation thermometry, as well as longer wavelength multi-colour detectors for ratio radiation thermometry. An uncooled T2SL detector on a GaSb substrate is demonstrated for measurement of a target temperature of 25 oC with SNR > 1. Cooling improves the detector’s performance, allowing operation at the thermo-electric cooler compatible temperature of 200 K. Further characterisation of a T2SL detector on a GaAs substrate demonstrates similar temperature dependence, suggesting challenges to the material growth for improved detector performance. Other potential challenges with T2SL development are identified and discussed.

The quantum dot infrared photodetector (QDIP) also offers the potential for longer wavelength multi-colour detection. Combination with an infrared algorithmic spectrometer (IRAS) offers flexibility for development of a versatile ratio radiation thermometer. The QDIP-IRAS combination is demonstrated to successfully reproduce arbitrary filter shapes from blackbody photocurrent measurements. Ratios computed using the IRAS correspond well with ratios computed from the arbitrary target filters.