Towards the Photonic Efficiency Enhancement of Si-Based High-Energy X-ray Detectors

Eldred Lee, Dartmouth College

Photo of Eldred Lee

Our everyday technologies are heavily influenced by light-matter interactions, or photonic interactions, that are engineered to our advantage. One of the wavelength regimes that has been deeply scrutinized for several decades is the hard (or high-energy) X-ray regime (λ=0.062-0.124nm; 20-50keV). However, the existing art pertaining to this wavelength regime has significant problems and limitations that result in inefficiency, increased maintenance, and undesirable outcomes.

Here, we investigate the inception of a novel yet simple hard X-ray photon energy attenuation layer (PAL) to advance the high-energy X-ray detection (20-50keV range) and to mitigate major limitations of state-of-the-art high-energy X-ray detection technologies such as scintillation and Si direct detection. These prevalent methods have low photon-to-photoelectron conversion efficiencies and often inefficient for >10keV photons. A two-layer design with a top thin film high-Z PAL and a bottom Si detector has been conceptualized using Monte Carlo N-Particle software (MCNP6.2) to demonstrate the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10keV via inelastic scattering suitable for efficient photoelectric absorption by Si. The computational results show that >10x increase in quantum yield from Si direct detection can be achieved. Such enhancement has been experimentally confirmed via a preliminary demonstration using monolithic integration of PAL on CMOS active pixel image sensors (APS). Several semiconductor cleanroom processing techniques such as lithography, deposition (PVD), and etch have been utilized to prototype PAL-integrated CMOS APS. The successful fabrication of the prototypes and preliminary experimental demonstration have enabled opening new doors for next-generation high-energy X-ray detection methods.

Abstract Author(s): Eldred Lee