Temperature activated 1.2 eV photoluminescence in semi‐insulating SiC wafers

Abstract

Temperature dependent photoluminescence (PL) spectroscopy was performed on semi-insulating and selfcompensated (non-vanadium doped) 6H-SiC wafers. PL intensity of the infrared band at 1.2 eV shows a remarkable increase up to two orders of magnitude, when the temperature was raised from 110 K to 175 K. We correlate the temperature dependence of the 1.2 eV PL band with dark and photoconductivity variation in the temperature range from 77 K to 300 K. Concurrently, thermally stimulated luminescence and thermally stimulated conductivity studies have been performed to provide information on the electron-hole traps participating in radiative transitions. A recombination model of the 1.2 eV band transition is proposed. 9 Ω.cm at room temperature can be produced by incorporating deep defects of presumably intrinsic origin [2]. Despite substantial progress in SiC technology which offers now-days 50.8 mm and 76.2 mm diameter wafers [3], the yield and performance of SiC based devices are still limited by structural defects in the substrates. Therefore, a strong motivation to better understand the origin and properties of compensating impurities and defects is evident. Spatially resolved optical metrology on full-size SiC wafers offers a non-contact and non-destructive characterization for quality assurance purposes [4].In this paper we report on thermal activation (increase) with raising temperature of the 1.2 eV photoluminescence (PL) band in SI 6H-SiC wafers. This unusual recombination effect was recently observed and explored in detail for visible 1.82 eV PL band in p-type SiC and attributed to thermal ionization of holes from partially compensated acceptor traps (Al or B) to the valance band and their radiative free-tobound recombination [5]. By monitoring the spatial distribution of the 1.82 eV PL and matching thermally stimulated luminescence (TSL) across the entire wafer, we proposed a simple experimental algorithm for fast non-destructive diagnostics of free carrier concentration topography in p-type SiC. The PL-TSL approach is employed in this paper to understand a mechanism of the PL activation with temperature on SI wafers.