Linearity of a silicon carbide photodiode in the deep-UV spectral region: implications on Doppler broadening thermometry

The linearity of the responsivity of a silicon carbide photodetector in the deep-ultraviolet has been studied using a variant of the so-called intensity-ratio method in view of the implementation of low-uncertainty Doppler-broadening thermometry in mercury vapours. To this purpose, coherent radiation at the wavelength of 254 nm has been produced by means of nonlinear mixing of two visible laser beams in a β-barium borate crystal. The linearity has been quantified as a function of the exposure power, variable in the range between 50 and 300 nW. It is shown that possible deviations from linearity are within the uncertainty of 4 10-5 (corresponding to one standard deviation). Such a performance makes the detector well suitable for the thermometric application.