Electrical nonuniformities and their impact on the electron mobility in semi-insulating SiC crystals

Semi-insulating (SI) 4H-SiC wafers grown by physical vapor transport (PVT) and by high temperature chemical vapor deposition (HTCVD) were investigated using Hall effects and van der Pauw measurements at elevated temperatures. It was found that the temperature dependence of both resistivity and electron mobility could only be measured at high temperatures. The measurable mobilities for PVT-grown vapors were never obtained from the peripheral part of the wafers but only on samples from the central part. High electron mobilities were measured for HTCVD-grown samples irrespective of their location. Macrononuniformities of electrical properties across the wafer were the cause of the low mobility values in SI-SiC crystals.