InGaP (GaInP) mesa p-i-n photodiodes for X-ray photon counting spectroscopy

S Butera,A M Barnett,A B Krysa,G Lioliou

doi:10.1038/s41598-017-10502-y

Abstract

In this paper, for the first time an InGaP (GaInP) photon counting X-ray photodiode has been developed and shown to be suitable for photon counting X-ray spectroscopy when coupled to a low-noise charge-sensitive preamplifier. The characterisation of two randomly selected 200 μm diameter and two randomly selected 400 μm diameter In0.5Ga0.5P p+-i-n+ mesa photodiodes is reported; the i-layer of the p+-i-n+ structure was 5 μm thick. At room temperature, and under illumination from an 55Fe radioisotope X-ray source, X-ray spectra were accumulated; the best spectrometer energy resolution (FWHM) achieved at 5.9 keV was 900 eV for the 200 μm In0.5Ga0.5P diameter devices at reverse biases above 5 V. System noise analysis was also carried out and the different noise contributions were computed.

Highlights

In0.5Ga0.5P (Ga0.5In0.5P) is a direct wide bandgap (~1.9 eV at room temperature1–3) ternary compound with a density of 4.5 gcm−3 and high X-ray and γ-ray linear absorption coefficients[4, 5]
For the areas of the photodiodes not covered by the top contact, X-ray quantum efficiencies (QE) of 53% and 44% were calculated at energies of 5.9 keV and 6.49 keV, respectively, using the Beer-Lambert law and assuming complete charge collection in the p and i layers
The linear attenuation coefficients used in the QE calculations were 0.145 μm−1 and 0.112 μm−1 at 5.9 keV and 6.49 keV, respectively[4, 5, 28]; these values are higher than many other semiconductors such as Si28, SiC4, GaAs4, and Al0.52In0.48P15, but lower than for CdZnTe5, 28

Summary

Introduction

In0.5Ga0.5P (Ga0.5In0.5P) is a direct wide bandgap (~1.9 eV at room temperature1–3) ternary compound with a density of 4.5 gcm−3 and high X-ray and γ-ray linear absorption coefficients[4, 5]. The combinations of the above properties make In0.5Ga0.5P potentially attractive for applications as a detector material for X-ray and possibly γ-ray photon counting spectroscopy. Due to their low leakage currents, wide bandgap semiconductor X-ray spectrometers can operate at room temperature and above without cooling systems[6,7,8]. The results reported in this paper are the first detection of X-rays with InGaP and the first demonstration of its suitability for photon counting X-ray spectroscopy These results are significant since GaP and InP were found to be not spectroscopic at room temperature. The work is of potential importance for the development of wide bandgap X-ray and γ-ray spectrometers for planetary and space science missions to extreme environments (such as Mercury, Venus, Jupiter, and Saturn), for space science instrumentation to study the near Sun environment, as well as for use in harsh terrestrial environments

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