An InGaAlAs-InGaAs two-colour detector, InAs photodiode and Si SPAD for radiation thermometry

This work aims to develop infrared detectors and to introduce a new measurement technique for infrared radiation thermometry. It consists of two-colour detectors for ratio thermometry, InAs photodiode for 3.43 m narrow band thermometer and photon counting thermometer using a Si single photon avalanche photodiode (SPAD). In addition to research in these detectors, a Monte Carlo model for modelling impact ionisation in Si was also developed. InGaAlAs is attractive material for multi-colour detection at wavelengths up to 1.7 m, as it is lattice matched to InP substrate. InGaAlAs-InGaAs two-colour detector was evaluated as a ratio thermometer. When compared to a commercial Si-InGaAs detector, the InGaAlAs diode produces slightly higher (lower) output than Si at temperature below (above) 500 °C, while the InGaAs diode in this work also produces slightly higher output than that in the commercial Si-InGaAs detector. The InGaAlAs and InGaAs diodes detect blackbody temperatures as low as 275 and 125 oC, respectively, with signal to noise ratios (SNRs) above 10. As a ratio thermometer, the two-colour InGaAlAs-InGaAs photodetector achieves a temperature error of 12.8 °C at 275 °C, but this improves with temperature to 0.1 °C at 450 °C. If the maximum temperature error of 2 °C is defined, the InGaAlAs-InGaAs is capable of detecting an object temperature down to 325 °C. These results demonstrate the potential of InGaAlAs-InGaAs two-colour photodetector for development of high performance two-colour array detectors for radiation thermometry and thermal imaging of hot objects. The InAs photodiode offers huge potential for infrared sensing applications at wavelengths above 1.7 m. The performance of InAs photodiode was evaluated for use in radiation thermometry at wavelengths beyond InGaAs photodiode. For uncooled InAs, it successfully measured a blackbody temperature of 50 oC with an acceptable error of 0.17 oC. In order to evaluate its performance as a 3.43 m narrow band thermometer, measurements were repeated with a narrow band filter. InAs was demonstrated to have lower temperature error than a commercial PbSe detector. The temperature error was 1.88 oC for InAs at 50 oC compared to 3.78 oC for PbSe. This suggests that InAs is ideally X. ZHOU III suited for applications requiring 3.43 m operating wavelength. Further improvement was achieved by cooling InAs to 200 K. It was found that a temperature as low as 37 oC, with an error of less than 0.5 oC, can be measured indicating its potential for human body temperature sensing. An alternative to using a photodetector with longer wavelength response is to increase the sensitivity of the photodetector via internal gain mechanisms such as impact ionisation. By employing a very high internal gain in SPAD, the photon counting technique was evaluated for radiation thermometry. Photon induced avalanche pulses were successfully measured at temperature as low as 225 oC with an error less than 2 oC using Si SPAD. This is significantly lower than the lower temperature limit of 400 oC in conventional Si photodiode based radiation thermometer. The photon counting technique is therefore demonstrated to be a feasible technique to achieve lower temperature sensing.