Development of an APD With Large Area and Thick Depletion Layer for Energetic Electron Measurements in Space

We report the performance of an Avalanche Photodiode (APD) that has a large-area (1 cm2) and a thick depletion layer (~30 μm) in application to electron measurements. It is shown that the dead layer is sufficiently thin for the detection of electrons at energies less than 10 keV; the lowest measurable energy is ~5 keV. We also confirmed that the energy resolution is not significantly deteriorated by the non-uniformity of the thickness of the dead layer or the internal gain. The energy resolution at the lower energy range (<;10 keV) is limited by the electric noise. Dependence of the electric noise on the detector size is also discussed. Furthermore, the effective multiplication profile in the normal direction is inferred from the experimental data.