# A graphene-on-silicon photodetector for low penetrating radiation

## TL;DR

A new graphene-on-silicon photodetector is developed to detect low penetrating radiation with high efficiency.

## Contribution

The use of a nearly transparent single-layer graphene to minimize the dead layer in photodetectors is novel.

## Key findings

- The photodiode achieves 100% uniformity in charge collection across its active area.
- It shows excellent responsivity in deep and vacuum ultra violet regions with ≥100% external quantum efficiency below 150 nm.
- The device's design reduces recombination of low-penetrating photons/particles in the dead layer.

## Abstract

We introduce an innovative graphene-on-silicon photodiode designed for low penetrating radiation. Its standout feature lies in its remarkably-thin dead layer in the entrance window, setting it apart from existing photodetectors. Conventional photodetectors suffer from sensitivity limitations in the low wavelength or energy, respectively, for light or particles, due to their shallow penetration depth. Most conventional photodiodes employ a junction implant which suffers from recombination of low-penetrating photons/particles within the dead layer. Instead, we utilise the nearly transparent properties of single-layer graphene to create a depletion layer that minimises the dead layer. We combine a single junction ring (highly doped \documentclass[12pt]{minimal}
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\begin{document}$$n^{++}$$\end{document} bias ring) with single-layer graphene. The graphene acts as a field plate, extended over the junction ring and covering the entire entrance window (5\documentclass[12pt]{minimal}
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\begin{document}$$mm^2$$\end{document} active area), while being electrically isolated by an ultrathin, high K dielectric layer. In operation, the photodiode undergoes depletion upon applying a reverse bias as expected, which primarily occurs within the region beneath the field plate. We conducted Transient Current Technique measurements as the best method to assess the charge collection uniformity of the device. Remarkably, the results reveal a consistent total 100% uniformity across the entire detector area. Nevertheless, while the collection time is position-dependent, increasing as the laser incidence point moves farther away from the bias ring, responsivity measurements show excellent response in both the deep ultra violet and vacuum ultra violet regions with \documentclass[12pt]{minimal}
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\begin{document}$$\ge$$\end{document} 100% external quantum efficiency at wavelengths below 150 nm.