Bulk lifetime and surface recombination velocity measurement method in semiconductor wafers

A noncontact and nondestructive measurement method is proposed to separately determine the bulk lifetime τb, and the front and backsurface recombination velocities S0 and Sw in the semiconductor wafer with different surface recombination velocities in the front and backsurfaces. The method is deduced based on a new analytical solution for photoconductivity decays derived for the wafer with different surface recombination velocities. The solution gives the expressions for a photoconductivity decay and a carrier profile under pulse laser excitation. The analytical relationship between the apparent (or effective) lifetime, S0, Sw, τb and a wafer thickness is given. The photoconductivity decay curve dependencies on various values of S0, Sw, and τb have been demonstrated. The algorithm is shown to separately extract τb, S0, and Sw. The algorithm is characterized by the measurement of two photoconductivity decay curves for pulse laser excitation on both surfaces of the wafer. The influence of the laser pulse width for the photoexcitation on the photoconductivity decays is discussed. The method can be readily applicable to noncontact photoconductivity decay measurement techniques using an electromagnetic wave such as a microwave.