Infrared absorption and annealing behavior of semi-insulating 4H SiC HTCVD substrates

Abstract

ABSTRACTInfrared absorption and resistivity are studied in two different types of semi-insulating (SI) 4H SiC substrates. In type A the silicon vacancy dominates the infrared absorption spectra whereas in type B the UD-1 defect dominates. Both types of substrates are still SI (> 105 Ω cm at 200°C) after annealing at typical CVD growth temperatures (1600°C). The type A material shows a decreasing absorption of the silicon vacancy after 1600°C at the same time as the resistivity decreases from high 107 Ω cm to mid 106 Ω cm measured at 200°C. The thermal activation energy of the resistivity for the type A material is 0.85 eV for temperatures above 250°C both before and after annealing. The type B material does not change with annealing, besides that the absorption increases in intensity with a 1600°C anneal. The resistivity is > 1010 Ω cm at 200°C and the thermal activation energy is 1.4 eV.The absorption measurements on the silicon vacancy also show that it is still present in the as-grown material after a 1600°C anneal. We interpret this as follows: The silicon vacancy is stable even at 1600°C and does not get mobile at 750°C as earlier suggested.