An InGaAlAs–InGaAs Two-Color Photodetector for Ratio Thermometry

We report the evaluation of a molecular-beam epitaxy grown two-color photodetector for radiation thermometry. This two-color photodetector consists of two p⁺in⁺ diodes, an In_0.53Ga_0.25Al_0.22As (hereafter InGaAlAs) p⁺in⁺ diode, which has a cutoff wavelength of 1180 nm, and an In_0.53Ga_0.47As (hereafter InGaAs) p⁺in⁺ diode with a cutoff wavelength of 1700 nm. Our simple monolithic integrated two-color photodetector achieved comparable output signal and signal-to-noise (SNR) ratio to that of a commercial two-color Si-InGaAs photodetector. The InGaAlAs and InGaAs diodes detect blackbody temperature as low as 275°C and 125°C, respectively, with an SNR above 10. The temperature errors extracted from our data are 4°C at 275°C for the InGaAlAs diode and 2.3°C at 125°C for the InGaAs diode. As a ratio thermometer, our two-color photodetector achieves a temperature error of 12.8°C at 275°C, but this improves with temperature to 0.1°C at 450°C. These results demonstrated the potential of InGaAlAs-InGaAs two-color photodetector for the development of high performance two-color array detectors for radiation thermometry and thermal imaging of hot objects.