Investigation of excess 1/f noise in CdTe single crystals

Experimental studies of noise characteristics of CdTe crystals, prepared using the travelling heater method, have been carried out. Three types of basic material were used: low-ohmic n-type with n = 5 × 1015 cm−3, semi-insulating n-type with n = 1.5 × 109 cm−3 and low-ohmic p-type with holes concentration p = 7 × 1014 cm−3. The noise measurements show that the dominant noise is 1/fn noise with parameter n in range from 0.9 to 1.5 and often very close to 1. The experimental value of 1/f noise is always much higher than the theoretical value which corresponds to the total value of free carriers in the sample. The voltage noise spectral density of 1/f noise depends on the quantity of free carriers in the sample. Free carriers are distributed uniformly throughout the homogenous part of the sample. But within the depleted region there is very low concentration of free carriers which increases exponentially in the direction from the contact area to the homogenous part of the sample. Analysis shows that the excess 1/f noise is caused by the low carrier concentration within the depleted region at the metal–semiconductor junction