Surface photovoltage simulated (785 nm illumination 1000 W/m²) on bulk silicon doped n-type at N_D = 10¹⁷ cm^–3 (a) as a function of the thickness of the surface defect layer showing a reduction to a constant value for thick charge neutral layer and (b) as a function of acceptor defect density N_DA (for defective layer thickness 0.1 μm) showing an initial reduction in SPV noted as a slight reduction in effective n-type doping, before N_DA significantly larger than N_D leads to the formation of an effective pn junction.