  High-energy (>20keV) X-ray photon detection at high quantum yield, high
spatial resolution and short response time has long been an important area of
study in physics. Scintillation is a prevalent method but limited in various
ways. Directly detecting high-energy X-ray photons has been a challenge to this
day, mainly due to low photon-to-photoelectron conversion efficiencies.
Commercially available state-of-the-art Si direct detection products such as
the Si charge-coupled device (CCD) are inefficient for >10keV photons. Here, we
present Monte Carlo simulation results and analyses to introduce a highly
effective yet simple high-energy X-ray detection concept with significantly
enhanced photon-to-electron conversion efficiencies composed of two layers: a
top high-Z photon energy attenuator layer (PAL) and a bottom Si detector. We
use the principle of photon energy down conversion, where high-energy X-ray
photon energies are attenuated down to and below 10keV via inelastic scattering
suitable for efficient photoelectric absorption by Si. Our Monte Carlo
simulation results demonstrate that 10-30x increase in quantum yield can be
achieved using PbTe PAL on Si, potentially advancing high-resolution,
high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors.
