Temperature dependent characterization of gallium arsenide X-ray mesa p-i-n photodiodes

Abstract

Electrical characterization of two GaAs p þ -i-n þ mesa X-ray photodiodes over the temperature range 0 C to 120 C together with characterization of one of the diodes as an X-ray detector over the temperature range 0 Ct o6 0 C is reported as part of the development of photon counting X-ray spectroscopic systems for harsh environments. The randomly selected diodes were fully etched and unpassivated. The diodes were 200 lm in diameter and had 7 lm thick i layers. The leakage current density was found to increase from (3 6 1) nA/cm À2 at 0 C to (24.36 6 0.05) lA/ cm À2 at 120 C for D1 and from a current density smaller than the uncertainty (0.2 6 1.2) nA/cm À2 at 0 C to (9.39 6 0.02) lA/cm À2 at 120 C for D2 at the maximum investigated reverse bias (15 V). The best energy resolution (FWHM at 5.9 keV) was achieved at 5 V reverse bias, at each temperature; 730 eV at 0 C, 750 eV at 20 C, 770 eV at 40 C, and 840 eV at 60 C. It was found that the parallel white noise was the main source of the photopeak broadening only when the detector operated at 60 C, at 5 V, 10 V, and 15 V reverse bias and at long shaping times (>5 ls), whereas the sum of the dielectric noise and charge trapping noise was the dominant source of noise for all the other spectra. V C 2016 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4944892]

High temperature GaAs X-ray detectors

“…The thicker i layer of the presently reported devices, compared to previously reported thinner GaAs p þ -i-n þ mesa photodiodes, [15][16][17][18] resulted in higher quantum detection efficiency and improved energy resolution at the investigated temperature range. The improved energy resolution of the presently reported spectrometer was attributed to the reduced white series, 1/f, and dielectric noise, all depending upon the capacitance of the photodiode.…”

“…18 A GaAs pixel p þ -i-n þ mesa photodiode detector reported by Bertuccio et al 25 had a leakage current density of 92 nA/cm 2 at 30 C and 33 kV/cm applied electric field. For comparison purposes, interpolating the leakage current density of D1 and D2 at 30 C (Fig.…”

“…8) was used to calculate the depletion layer width, W D , of both diodes as a function of applied reverse bias, at all the investigated temperatures. 18 The calculated depletion layer capacitance at 100 C and -20 C of both diodes can be seen in Fig. 9.…”

“…The improved energy resolution of the presently reported spectrometer was attributed to the reduced white series, 1/f, and dielectric noise, all depending upon the capacitance of the photodiode. However, the better energy resolution (FWHM at 5.9 keV) achieved at 60 C with a spectrometer employing a 7 lm i layer thickness GaAs p þ -i-n þ mesa photodiode (0.84 keV), 18 compared to the currently reported 10 lm i layer thickness GaAs p þ -i-n þ mesa photodiode, D1, (0.92 keV) was attributed to the lower leakage current of the 7 lm i layer device (27 pA) compared to that of D1 (43 pA), in the specific operating conditions. The dielectric noise, which was found to decrease from 1.13 keV at 80 C to 0.59 keV at -20 C for S1, and from 1.50 keV at 80 C to 0.64 keV at -20 C for S2, was the dominant source of noise in the temperature range 80 C to -20 C, at all investigated shaping times, at -5 V reverse bias, apart from shaping times !3 ls at 80 C, !6 ls at 60 C, and ¼ 10 ls at 40 C, where the parallel white noise dominated.…”

“…16 Systematic study of fabrication techniques for GaAs p þ -i-n þ mesa X-ray photodiodes with 7 lm i layer thickness investigated the effects of wet chemical etchants and etch depths on the dark currents of such devices; a fully etched 400 lm diameter diode had a FWHM at 5.9 keV of 1 keV, at room temperature. 17 The energy resolution (FWHM at 5.9 keV) as a function of temperature of similar GaAs p þ -i-n þ mesa X-ray photodiodes with 7 lm i layer thickness was studied and found to increase from 0.73 keV at 0 C to 0.84 keV at 60 C. 18 Results characterizing GaAs p þ -in þ mesa X-ray photodiodes with 10 lm i layer thickness at room temperature showed an energy resolution of 0.625 keV (200 lm diameter device) and 0.740 keV (diameter device) at 5.9 keV, at room temperature. 19 Here, results across the temperature range of 100 C to -20 C are presented for two GaAs p þ -i-n þ mesa X-ray photodiodes with 10 lm i layer thickness and different (200 lm and 400 lm) diameters.…”