Nature of the 1/f noise in 6H-SiC

The phenomenon of 1/f noise in SiC has been studied in detail for the first time. Spectral noise density dependences for n-type 6H-SiC samples with doping level Nd-Na approximately=1017 cm-3 were measured at 300-600 K over the frequency range from 20 Hz to 20 kHz. The value of the Hooge parameter alpha for 1/f noise is in the range from 5*10-5 to 10-3. A low value of a indicates a rather high degree of structural perfection of the material. The value of the 1/f noise depends rather weakly on temperature in the range 300-450 K. The sources of the 1/f noise are distributed uniformly in the channel of SiC JFETs used for studying low-frequency noise in 6H-SiC. For all samples, two local levels can be plainly observed from noise measurements. A frequency-dependent decrease of the 1/f noise was observed on the injection of minority carriers (holes) with very small concentration. Holes have been injected into the n-channel of FETs due to the forward bias on the gate p+-n junction. The change in the low-frequency noise due to the appearance of the holes is qualitatively similar to the illumination-induced modification of 1/f noise in n-GaAs and n-Si observed and explained theoretically earlier. It is supposed that bulk 1/f noise in n-SiC is due to fluctuations in the occupancy of the levels that form the density-of-states tail near the conduction band edge.