30 μm thick GaAs X-ray p + -i-n + photodiode grown by MBE

Lioliou, G.; Poyser, C.L.; Butera, S.; Campion, R.P.; Kent, A.J.; Barnett, A.M.

Abstract

7 8 A GaAs p +-in + photodiode detector with a 30 μm thick i layer and a 400 μm diameter was processed using 9 standard wet chemical etching from material grown by molecular beam epitaxy. The detector was 10 characterized for its electrical and photon counting X-ray spectroscopic performance at temperatures from 60 11 °C to-20 °C. The leakage current of the detector decreased from 1.247 nA ± 0.005 nA (= 0.992 μA/cm 2 ± 12 0.004 μA/cm2) at 60 °C to 16.0 pA ± 0.5 pA (= 12.8 nA/cm2 ± 0.4 nA/cm2) at-20 °C, at the maximum 13 investigated applied reverse bias,-100 V (corresponding to an applied electric field of 33 kV/cm). An almost 14 uniform effective carrier concentration of 7.1 × 10 14 cm-3 ± 0.7 × 10 14 cm-3 was found at distances between 1.7 15 μm and 14 μm below the p +-i junction, which limited the depletion width to 14 μm ± 1 μm, at the maximum 16 applied reverse bias (-100 V). Despite butterfly defects having formed during the epitaxial growth, 55 Fe X-ray 17 spectra were successfully obtained with the detector coupled to a custom-made charge-sensitive preamplifier; 18 the best energy resolution (Full Width at Half Maximum at 5.9 keV) improved from 1.36 keV at 60 °C to 0.73 19 keV at-20 °C. Neither the leakage current nor the capacitance of the GaAs detector were found to be the 20 limiting factors of the energy resolution of the spectroscopic system; noise analysis at 0 °C and-20 °C revealed 21 that the dominant source of noise was the quadratic sum of the dielectric and incomplete charge collection 22 noise. 23 24 Keywords: Gallium Arsenide; GaAs; X-ray spectroscopy; wide bandgap; high temperature. 25 26 1. Introduction 27 28 The relatively low number of thermally generated carriers [1], high radiation hardness [2-5], and high stopping 29 power [6] of GaAs devices, compared to traditional narrow bandgap semiconductor materials, such as Si, make 30 them attractive options for a number of applications in radiation detection for space science [7] and medicine 31 [8]. However, if GaAs devices are ever to replace traditional semiconductor X-ray detectors, such as Si 32 photodiodes, further research is required to improve the maturity of GaAs technology. One of the areas 33 needing development is material growth and processing [6]. 34 35 The thickest and the best performing (in terms of energy resolution) GaAs X-ray detectors so far produced 36 were grown by chemical vapor phase deposition (CVPD): ultrapure epitaxial layers of 40 μm [9], 150 μm [10], 37 325 μm [11], and 400 μm [12] thickness were successfully grown on n + semi-insulating GaAs substrates. The 38 devices had a p +-in + structure, with Au/Pt/Ti Schottky contacts on the p + layer, and guard rings. The devices 39 had low leakage current densities at room temperature (as low as 4 nA/cm 2 [12]), and when coupled to 40 ultra-low-noise preamplifier electronics, were able to achieve an energy resolution of 266 eV at 5.9 keV Full 41 Width Half Maximum [9]. 42 43 Energy resolutions as good as those reported by Owens et al. [9] have never since been replicated with GaAs 44 X-ray spectrometers, despite considerable effort. The presence of impurities within the active volume of GaAs 45 detectors can lead to charge carrier trapping and recombination, which has two direct effects in the detector's 46 spectroscopic performance: 1) reduction in the signal amplitude, and 2) energy resolution degradation due to 47 additional statistical fluctuations in the signal charge [13]. The probability of charge carrier 48 trapping/recombination increases with increased device thickness, and thus, when this is a dominant effect, it 49 places limitations on the thickness of GaAs devices that can still achieve an adequate energy resolution. 50 However, this is balanced with the need for thick active layer GaAs X-ray detectors due to the reduction of the 51 white series noise contribution of the X-ray detector and the increase of its quantum detection efficiency, as 52 the active layer thickness increases. 53 a) Corresponding author. Tel.: [phone].

Citation

Lioliou, G., Poyser, C., Butera, S., Campion, R., Kent, A., & Barnett, A. (2019). 30 μm thick GaAs X-ray p + -i-n + photodiode grown by MBE. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 946, Article 162670. https://doi.org/10.1016/j.nima.2019.162670

• Journal Article Type: Article
• Acceptance Date: Aug 30, 2019
• Online Publication Date: Sep 5, 2019
• Publication Date: Dec 1, 2019
• Deposit Date: Sep 18, 2019
• Publicly Available Date: Sep 6, 2020
• Journal: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• Print ISSN: 0168-9002
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 946
• Article Number: 162670
• DOI: https://doi.org/10.1016/j.nima.2019.162670
• Keywords: Gallium arsenide; GaAs; X-ray spectroscopy; Wide bandgap; High temperature
• Public URL: https://nottingham-repository.worktribe.com/output/2628309
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0168900219311544
• Additional Information: This article is maintained by: Elsevier; Article Title: thick GaAs X-ray p-i-n photodiode grown by MBE; Journal Title: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.nima.2019.162670; Content Type: article; Copyright: © 2019 Elsevier B.V. All rights reserved.
• Contract Date: Sep 18, 2019