Capacitively Coupled GaAs p-i-n/Substrate Photodetector with Ohmic Contacts on Lightly Doped n-GaAs for Hard X-Ray Imaging

TL;DR

This paper introduces a capacitively coupled GaAs p-i-n/substrate photodetector designed for high-energy X-ray detection, demonstrating fabrication techniques and initial performance metrics relevant for 3D X-ray imaging applications.

Contribution

It presents a novel fabrication strategy for GaAs photodetectors with ohmic contacts on lightly doped n-GaAs, advancing toward 3D X-ray detection capabilities.

Findings

Detects pulses of 10^6 electrons at 80 MHz laser

Fabrication method achieves ohmic contacts on lightly doped GaAs

Preliminary insights into performance for future 3D X-ray detectors

Abstract

In this work, we present a capacitively coupled GaAs p +-i-n/substrate photodetector (CC-GaAs PIN/S PD), which also represents a preliminary step toward 3D detection (x, y, time) of high-energy X-ray pulses. Although the final 3D detector will be based on a separate absorption and multiplication avalanche photodiode (SAM APD) design, the present device exhibits characteristics that offer valuable insights into the performance expected once a multiplication layer is incorporated into the final device. In particular, we present a fabrication strategy that employs multi-step annealing in the low-temperature range of 280 330C to achieve Cr/Au ohmic contacts on lightly doped n-GaAs, which is also required for the photodetector architecture. Simultaneously, the same contact preparation process was applied to p + GaAs. Furthermore, the fabricated CC-GaAs PIN/S PD includes an additional contact designed to reduce leakage current by applying the same bias as that of the anode. Measurements performed using an 80 MHz laser demonstrated the photodetector's ability to detect pulses corresponding to 10^6 electrons per pulse.