Spectral responsivity and linearity evaluation of silicon carbide photodiodes for ultraviolet detection

The absolute spectral responsivities of four commercial silicon carbide (SiC) photodiodes (PDs) in the ultraviolet (UV) range were investigated. The nonlinearities of these SiC PDs in under-filled illumination condition were also investigated in the UV range under non-bias and reverse-bias voltage conditions. All Si PDs exhibited almost linear characteristics at a wavelength of 266 nm. Different supralinearity trends were observed for the SiC PDs at wavelengths longer than those for their maximum spectral responsivities, and the maximum value reached 120% under non-bias voltage condition. By applying a reverse-bias voltage, the supralinearity values of all SiC PDs decreased due to the expansion of their depletion layers and an increase in the initial saturation photocurrents. The nonlinearity of the SiC PDs in over-filled illumination condition was also investigated. When comparing the supralinearity at 355 nm, the results in over-filled illumination condition were similar to those in under-filled illumination condition up to a certain photocurrent. At higher photocurrents, however, the results in over-filled illumination condition were lower, except for one type of SiC PD. This is because few recombinations for generating supralinearity occur near the electrode of the selected SiC PDs. These experimentally measured results of nonlinearity and absolute spectral responsivity contribute to accurate optical measurements using SiC PDs in the UV range.