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

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.

InGaP electron spectrometer for high temperature environments

“…Such dark current was slightly higher than that observed in ref. 30 (at 30 V and 20 °C, 2 pA against 0.5 pA) and ref. 31 (at 15 V and 100 °C, 4 pA against 1.5 pA), where similar devices were studied.…”

“…At the same temperature and shaping time a parallel white noise of 11 e − rms was estimated (the Si JFET leakage current was assumed to be 1 pA). At 20 °C, a known 1/ f noise of 2 e − rms and a known dielectric noise of 53 e − rms (using dielectric dissipation factors of 4.2 × 10 −3 for In 0.5 Ga 0.5 P 30 and 2 × 10 −3 for Si 45 ) were calculated, these noise contributions are shaping time independent. It should be noted that a direct measurement of the Si JFET leakage current and capacitance could not be performed, the values used in the calculation are based on the Si JFET datasheet 46 .…”

“…Recently, the III-V ternary compound In 0.5 Ga 0.5 P (bandgap = 1.9 eV at room temperature 27–29 ) has been investigated as a detector material for photon counting X-ray spectroscopy. Photon counting spectroscopic X-ray photodiodes made of In 0.5 Ga 0.5 P have been reported working at room temperature 30 and at up to 100 °C 31 , with energy resolutions (Full Width at Half Maximum) at 5.9 keV of 840 eV and 1.27 keV at 20 °C and 100 °C, respectively. Table 1 compares the energy resolution at 5.9 keV of X-ray spectrometers made of competitive semiconductors 32–35 .…”

“…The use of InGaP for photon counting spectrometers is relatively new; only recently has their suitability for photon counting X-ray spectrometers at 20 °C 30 and above 31 been reported in the literature; temperature tolerant In 0.5 Ga 0.5 P spectrometers are interesting, since GaP and InP (InGaP binary relations) were found to not be spectroscopic even at 20 °C. The advantages of InGaP include radiation hardness, temperature tolerance, and higher linear absorption coefficients.…”

GaAs/Al0.8Ga0.2As separate absorption and multiplication region x-ray spectroscopic avalanche photodiodes

“…Due to the limitations of narrow bandgap (typically Si) X-ray spectrometers commonly in use today [1,2], a variety of wide bandgap materials, such as GaAs [3][4][5][6][7], diamond [8,9], SiC [10][11][12], In0.5Ga0.5P [13,14], Al0.52In0.48P [15][16][17], and AlxGa1-xAs [18][19][20][21], have been investigated as potential X-ray detector replacements. The cooling systems and radiation shielding often required for Si X-ray spectrometers [22] place substantial burdens on spacecraft mass, volume, and power consumption, limiting their suitability for certain space science applications (e.g.…”