Thick 4H-SiC epitaxial detectors for high-resolution radiation detection in harsh environment

Abstract

We report on the fabrication and characterization of a high-resolution Schottky barrier radiation detector for high temperature (HT) applications using high quality 150 𝜇m thick n-4H-SiC epitaxial layers with an ultra-low micropipe density of ≤0.1 cm-2. To evaluate the depletion region parameters of the detector, it was first characterized temperature- dependent capacitance voltage (C-V-T) measurements which showed barrier heights Φ𝐵 ranging from 2.09 to 2.24 eV and a carrier concentration of ~2 x 1014 cm-3 at room temperature (RT) which linearly increased at a rate of 9.65 x 1010 cm-3/K. From the depletion region simulation studies, it was shown that the change in doping concentration with temperature (T) can increase the needed bias to fully capture charged particles by up to 9V for 241Am and over 30V for a higher energy particles from 213Po. To examine the barrier properties and leakage currents of the detectors, we have systematically characterized temperature-dependent current - voltage measurements (I-V-T). The forward bias characteristics showed two linear regions - a low voltage region corresponding to a Shockley-Read-Hall (SRH) recombination center at 𝐸𝐶 − 0.93 eV and an upper region which corresponded to the barrier height of 2.02 eV. The reverse bias leakage currents were measured to be ~6 pA at ~65V at 300K implying a high signal to noise ratio (SNR) at RT and exhibited a current of less than 1 nA until 500K suggesting that detector should be operable with high SNR at ~200 oC. The Arrhenius plot of the reverse I-V-T showed an activation energy of 0.11 eV up to 400K and then 0.73 eV for 450K to 600K suggesting that most of the excess current at HT is derived from deep level state Z1/2 recombination center. Deep level transient spectroscopy (DLTS) results showed low defect concentrations of ~1011 cm-3 confirming that charge loss from trapping is negligible. Density functional theory (DFT) calculations suggested that the measured trap levels corresponded primarily to carbon (C) vacancies while the level at 0.93 eV corresponded to Si vacancies near the surface. The pulse height spectra (PHS) of the detector showed an excellent RT energy resolution of 0.55% FWHM at 5486 keV alpha particles after gaussian correction owed gamma response at 59.54 keV.