On the Transient Negative Photoconductance in n-type Czochralski Silicon

A transient negative photoconductance phenomenon is observed in n-type Czochralski silicon wafers. After a pulsed light excitation, the measured photoconductance drops to negative values and then increases to the original zero. The paper details how transient negative photoconductance is predicted by the Shockley-Read-Hall rate equations for a system of two defects. For this to occur, one defect must act as a majority carrier trap, and the other must be a relatively faster recombination channel. The specific conditions of these defects for a negative photoconductance to occur are derived analytically. Numerical modeling of this system shows good agreement with the experimental results. Finally, a method to extract the trap parameters from negative photoconductance for a sample with temperature-independent capture cross sections is demonstrated.