Abstract: A method and device is provided for determining defects within a single crystal substrate. The methodology includes a surface photovoltage (SPV) technique in which the magnitude of non-linearity is quantified and correlated to defects within the crystal lattice. The correlation factor is determined in a rapid and efficient manner using least square correlation methodology without having to determine diffusion length and incur difficulties associated therewith. Obtaining a quantifiable least square correlation factor allows the operator to quickly determine the amount of crystalline damage often encountered by, for example, ion implantation. In addition, the operator can determine the relative depth and position of defective crystalline layers within the substrate based upon demarcations between monotonically and non-monotonically aligned points plotted in a graph of reciprocal photovoltage versus reciprocal absorption coefficient.