Al0.2Ga0.8As 2 [formula omitted] 2 square pixel X-ray photodiode array

M.D.C Whitaker,G Lioliou,A.M Barnett

doi:10.1016/j.nima.2018.05.032

Abstract

A monolithic 2 × 2 square pixel Al0.2Ga0.8As p+–i–n+ mesa X-ray photodiode array (each photodiode area 200 μm by 200 μm, 3μm i layer) has been fabricated from material grown by MOVPE. The array was electrically characterised across the temperature range 100 °C to -20 °C. Each pixel’s response to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα=5.9 keV; Mn Kβ=6.49 keV) was investigated across the temperature range 30 °C to -20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 0.76 keV ± 0.06 keV (with 30 V reverse bias applied to the detector). The measured energy resolution is the best so far reported for AlGaAs X-ray photodiodes at 20 °C. It is also the first time a small AlGaAs X-ray photodiode array has been demonstrated. Due to the temperature tolerance and the radiation hardness of AlGaAs, such detectors are expected to find utility in future space science missions exposed to intense radiation environments, for example missions to study the Jovian or Saturnian aurorae and high temperature planetary surfaces.

Highlights

Conventional Si and Ge X-ray spectrometers often require significant shielding and cooling mechanisms in order to function in extreme environments
The relatively wide bandgap of AlxGa1-xAs (e.g. 1.67 eV for x = 0.2) [7] enables superior energy resolutions at high temperature as a result of lower thermally induced leakage currents compared with narrower bandgap devices [8]
Capacitance as a function of applied forward and reverse bias was measured for each Al0.2Ga0.8As p+-i-n+ pixel (D1, D2, D3, and D4) across the temperature range 100 °C to -20 °C, using an HP 4275A LCR Meter and a Keithley 6487 picoammeter/voltage source to bias the detectors

Summary

Introduction

Conventional Si and Ge X-ray spectrometers often require significant shielding and cooling mechanisms in order to function in extreme environments (e.g. temperatures >> 20 °C). Technologies which enable the reduction of the requirements for these aspects are potentially very attractive. AlxGa1-xAs has received particular attention as a promising material for X-ray [1] [2] [3] [4] and beta particle [5]. The relatively wide bandgap of AlxGa1-xAs (e.g. 1.67 eV for x = 0.2) [7] enables superior energy resolutions at high temperature as a result of lower thermally induced leakage currents compared with narrower bandgap devices [8]. The larger X-ray linear attenuation coefficient of AlxGa1-xAs

Results

Discussion

Conclusion