Charge Transport and Multiplication in Lateral Amorphous Selenium Devices Under Cryogenic Conditions

TL;DR

This study systematically characterizes charge transport and avalanche behavior in lateral amorphous selenium devices at cryogenic temperatures, revealing temperature-dependent mechanisms and establishing foundational data for low-temperature photodetector development.

Contribution

First comprehensive analysis of cryogenic avalanche and transport mechanisms in lateral amorphous selenium devices, advancing low-temperature photodetector technology.

Findings

Effective quantum efficiency decreases with temperature.

Transport mechanisms favor hopping and tunneling at low temperatures.

Avalanche behavior transitions directly from detrapping at 93 K.

Abstract

Cryogenic photon sensing for high-energy physics motivates photosensor technologies that combine large-area scalability with internal gain and stable operation at low temperature. Amorphous selenium is a promising photoconductor, yet its field- and temperature-dependent transport and avalanche response in lateral geometries have not been systematically established. This work reports field-resolved photocurrent measurements of lateral a-Se devices from 93 K to 297 K under 401 nm excitation at fields up to 120 V/um. Below avalanche onset, the external quantum efficiency was described by the Onsager model, yielding effective post-thermalization separations that decrease with decreasing temperature. The field-assisted detrapping region was evaluated using several transport models, with the data favoring field-assisted hopping and thermally-assisted tunneling as the mechanisms that best capture the temperature evolution of the photocurrent. The boundaries between field-assisted detrapping, transport-limited conduction, and avalanche shift with temperature; at 93 K the response transitions directly from detrapping into avalanche. Avalanche multiplication was analyzed using the Lucky-drift model. These results provide the first systematic characterization of cryogenic avalanche behavior in lateral a-Se detectors and establish quantitative trends relevant to low-temperature, high-gain photodetector design.