Picosecond Time Resolution with Avalanche Amorphous Selenium

Abstract

Ultrafast photodetection has traditionally been performed with crystalline photodetectors, which tend to suffer from low production yield, suboptimal detection efficiency, and operational limitations that restrict their potential applications. Amorphous selenium is a unique, disordered photosensing material in which carrier transport can be shifted entirely from localized to extended states where holes get hot, resulting in deterministic, non-Markovian impact ionization avalanche, causing selenium to exhibit characteristics similar to crystalline photoconductors. For the first time, we have fabricated a multiwell selenium detector using nanopillars that achieves both avalanche gain and unipolar time-differential charge sensing. We experimentally show how these features together improve selenium’s temporal performance by nearly 4 orders of magnitude, allowing us to achieve picosecond timing jitter suitable for a variety of ultrafast applications. Such a detector would be a viable low-cost, high production yield alternative for picosecond photodetection and imaging.

Recent Developments of Amorphous Selenium-Based X-Ray Detectors: A Review

“…There are two important features of the avalanche process inside a-Se: firstly, the slow charge carriers inside a-Se, i.e. electrons, are not involved in this process [1], [40], [42]- [45]; secondly, the avalanche process is non-Markovian and, with a design that suppresses depthdependent gain, the additional noise from the avalanche has limited impact on the signal to noise ratio [42], [46], [47].…”

“…Another recently prototyped design combining UTD and HARP with the insertion of Frisch grid was fabricated using nanoscale structures [42]. The detector has a high-density multiwell geometry with nanoscale pillars and one layer of nano-Frisch grid.…”

“…7. The schematic diagram of the picosecond multiwell selenium detector experiment (adapted from [42]). Fig.…”

Ultralow Dark Currents in Avalanche Amorphous Selenium Photodetectors Using Solution-Processed Quantum Dot Blocking Layer

“…Efficient sensing and imaging of low-light signals down to the single photon level with a true solid-state photomultiplier tube (PMT) has been a long-standing quest with a wide range of applications in medical imaging, , astronomy, and spectroscopy, and the rapidly developing fields of quantum optics and quantum information science . The discovery of novel two-dimensional (2D) layered van der Waals solids and their heterostructures, especially those utilizing selenide-based binary compounds, have attracted great attention in photonics and optoelectronics due to the promise of achieving ballistic avalanche phenomena in a deterministic nature .…”

“…Amorphous selenium ( a -Se) as a photoconductive film is poised to revolutionize photodetection through its unique single carrier avalanche multiplication process. , Solid-state selenium sensors utilized in X-ray imagers, operated below the avalanche threshold field ( F th ), have achieved considerable commercial success as a -Se is a wide bandgap semiconductor amenable to large-area deposition with low leakage current at room temperature. Additionally novel a -Se sensor designs incorporating high granularity Frisch grids have experimentally demonstrated a nearly 4 orders of magnitude improvement in temporal resolution compared to conventional planar geometries, enabling ultrafast picosecond photodetection with a -Se. , …”