Silicon carbide photodiodes: future solar-blind EUV/soft x-ray detectors

Abstract

The responsivity of a SiC photodiode was measured with synchrotron radiation in the deep UV and for the first time in the EUV and soft x-ray wavelength regions. A peak responsivity was 200 mA/W at 270 nm wavelength and 60 mA/w at 13 nm in the EUV. Extended measurements at shorter wavelengths demonstrated a responsivity up to 80 mA/W for wavelengths as short as 1.5 nm. The responsivity was calculated by an optical model that accounted for the reflection and absorption of the incident electromagnetic wave, the pair creation energy in the 6H-SiC device, and the variation of the charge collection efficiency (CCE) with depth into the device. The calculated responsivity was in excellent agreement with the measured responsivity and with the structure of the p-n junction photodiode. The measured visible light sensitivity was a factor of 100 lower than that of a silicon photodiode. These new results open up several possible applications for SiC photodiodes, including the selective detection of EUV and soft x-ray radiation without contamination by visible and IR wavelengths. SiC photodiodes have also been proven to withstand prolonged UV exposure and extreme temperatures, thus making them nearly ideal detectors for fiiture solar and space missions where absolutely calibrated EUV and soft x-ray intensities must be accurately measured.