Study Reveals Fundamental Limits of Trap-assisted Photomultiplication in Photodiodes
A new theoretical analysis shows that photodiodes using trap-assisted current injection cannot fundamentally enhance detector sensitivity beyond what unity-gain devices achieve, despite appearing to exceed quantum efficiency of one. The gain mechanism is self-limiting because the injection process that amplifies current simultaneously degrades the trap state enabling that gain. This finding challenges how such devices are compared in the literature and establishes thermodynamic limits on their performance.
Researchers have developed an analytical framework to understand the fundamental constraints of trap-assisted photomultiplication in photodiodes. While these devices can exhibit internal gain with apparent quantum efficiencies exceeding unity, the study demonstrates this gain cannot improve detector sensitivity beyond the intrinsic limits of unity-gain photodiodes. The gain mechanism is inherently self-limiting: the same injection process that amplifies current accelerates relaxation of the trap state responsible for gain. The nonlinear response varies depending on trap energy distribution and recombination pathways, making single gain measurements unreliable for device comparison. The analysis treats trap occupancy and injection as coupled stochastic processes, revealing that internal gain introduces a noise penalty from dissipative dynamics. While gain can suppress downstream readout noise, it cannot reduce the fundamental noise floor established by the primary photodetection process itself.
What's missing
The study does not discuss potential practical applications where suppressing downstream readout noise might provide value despite not improving fundamental sensitivity limits, nor does it address experimental validation of these theoretical predictions.
What different sources said
- arXiv physicsCenter
Limits of Trap-assisted Photomultiplication Gain
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