Experiments at synchrotron radiation sources and X-ray Free-Electron Lasers
in the soft X-ray energy range (250eV--2keV) stand to benefit from the
adaptation of the hybrid silicon detector technology for low energy photons.
Inverse Low Gain Avalanche Diode (iLGAD) sensors provide an internal gain,
enhancing the signal-to-noise ratio and allowing single photon detection below
1keV using hybrid detectors. In addition, an optimization of the entrance
window of these sensors enhances their quantum efficiency (QE). In this work,
the QE and the gain of a batch of different iLGAD diodes with optimized
entrance windows were characterized using soft X-rays at the
Surface/Interface:Microscopy beamline of the Swiss Light Source synchrotron.
Above 250eV, the QE is larger than 55% for all sensor variations, while
the charge collection efficiency is close to 100%. The average gain depends
on the gain layer design of the iLGADs and increases with photon energy. A
fitting procedure is introduced to extract the multiplication factor as a
function of the absorption depth of X-ray photons inside the sensors. In
particular, the multiplication factors for electron- and hole-triggered
avalanches are estimated, corresponding to photon absorption beyond or before
the gain layer, respectively.Comment: 16 pages, 8 figure