Measurement of the thickness of an insensitive surface layer of a PIN photodiode

We measured the thickness of an insensitive surface layer of a PIN photodiode, Hamamatsu S3590-06, used in the Tokyo Axion Helioscope. We made alpha-particles impinge on the PIN photodiode in various incidence angles and measured the pulse height to estimate the thickness of the insensitive surface layer. This measurement showed its thickness was 0.31 ± 0.02 μ m on the assumption that the insensitive layer consisted of Si. We calculated the peak detection efficiency for low energy X-rays in consideration of the insensitive layer and escape of X-rays and Auger electrons. This result showed the efficiency for 4– 10 keV X-rays was more than 95%.