Collaborative Research: Solid-State Selenium Photo-multiplier with a High-K Dielectric Blocking Layer for High, Noise-free Avalanche Gain

Proposal Number: 2048390 (Lead), 2048397 & 2048400 Principal Investigator: Amirhossein Goldan (PI), Ayaskanta Sahu (Co-PI) & Dragica Vasileska (Co-PI)

Title: Collaborative Research: Solid-State Selenium Photo-multiplier with a High-K Dielectric Blocking Layer for High, Noise-free Avalanche Gain Institution: State University of New York Stony Brook (Lead), New York University & Arizona State University Nontechnical Abstract

The search for a solid-state photodetector that mimics the behavior of a classical vacuum photomultiplier tube has been a long-standing quest because of the highly stochastic impact ionization process in single-crystalline semiconductors. Amorphous selenium is the only disordered semiconductor that produces avalanche multiplication gain while exhibiting a very low excess noise factor due to non-ballistic and single-carrier impact ionization.

The primary objective of this project is to fabricate and characterize high sensitivity solid-state photomultipliers by fully exploiting the deterministic avalanche multiplication properties of amorphous selenium via a solution-processed oxide blocking layer with a high dielectric constant. From the theoretical perspective, the noise-free nature of the hole impact ionization process will be modeled in amorphous selenium to enhance scientific insight into hot carrier transport in disordered structures.

The resulting technology can be utilized in a wide range of advanced fields and applications such as medical diagnostic imaging, high energy physics, Cherenkov imaging detectors and trackers, optical communications, and time-domain spectroscopy. The broader impact of this project involves training of students (graduate, undergraduate, and under-represented) in this exciting field of research, and dissemination of tools and materials online.

Technical Abstract

Amorphous selenium is poised to revolutionize solid-state photodetection and imaging through its noise-free single-carrier avalanche multiplication gain. Currently, to achieve high dynamic range and linear mode operation, the detectors used for low-light detection are almost exclusively made of vacuum photomultiplier tubes, where only electrons exist and are multiplied deterministically by the dynodes.

However, photomultiplier tubes are bulky, have poor quantum efficiency in the visible spectrum, and cannot be made into an imaging array. Although solid-state crystalline semiconductors are also used as avalanche photodiodes, the amount of enhancement in signal-to-noise ratio is often severely limited by excess noise due to the stochastic nature of the avalanche impact ionization process.

Thus, the optimal signal-to-noise ratio typically occurs at very low gains. This work proposes a true solid-state alternative to the vacuum photomultiplier tube using amorphous selenium as the bulk avalanche i-layer, which is a unique disordered photosensing material. In this amorphous selenium layer, hole carrier transport can be shifted entirely from localized to extended states, where holes experience deterministic and non-Markovian impact ionization avalanche.

To utilize this material property in devices and imagers, and to achieve reliable and repeatable avalanche gain without irreversible breakdown, a non-insulating n-type hole-blocking/electron-transporting layer is required. This work proposes use of room-temperature, solution-processed quantum-dots, as the high-k dielectric hole-blocking n-layer. Solution synthesis of colloidal quantum dots allows for high-quality stoichiometric and vacancy-free crystals with potential for room-temperature deposition in the desired reverse-biased p-i-n structure, without inducing any crystallization of amorphous selenium, as opposed to other incompatible high-temperature fabrication techniques.

This methodology enables, for the first time, reaching an avalanche gain of 10E6 or beyond using a solid-state material. Computational models that explore the physics of the hole blocking layers shall be created to understand and optimize device performance. To this effect, an in-house kinetic Monte Carlo code used to model transport through defects will be developed.

Next, an in-house full-band Monte Carlo simulator, that utilizes the full band structure of selenium, will be established to examine the hole impact ionization process in bulk selenium. As a final step, the kinetic and the full-band Monte Carlo results will be coupled for computer-aided design simulations, to provide design guidelines for the fabrication of more efficient selenium photomultipliers.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.