Patent ID: 7265571

Claim:
Method for determining a characteristic of a semiconductor sample having a surface, comprising: (a) simultaneously illuminating an area on the surface of a semiconductor sample with superimposed exciting light beams with a plurality of different wavelengths, (b) modulating the light beams of different wavelengths with the same frequency, but different phases, (c) selecting a modulation function and phases of the modulation function, wherein the modulation function sums photon fluxes of all light beams at all times within a tolerance range, and wherein the tolerance range is less than the sum of all photon fluxes, (d) simultaneously phase-dependent measuring of the components of the surface photo voltage caused by the different light beams, and (e) determining a characteristic of the semiconductor sample based on the relationships between the components and the respective wavelengths, and outputting the determined characteristic; wherein the characteristic to be determined is the diffusion length of minority charge carriers, and the determination of the diffusion length of the minority charge carriers is determined by fitting value pairs of surface photo voltage ΔV SPV and wavelengths λ or the penetration depth z of the light into the equation Δ ⁢ ⁢ V SPV ⁡ ( λ ) Φ eff ⁡ ( λ ) Δ ⁢ ⁢ V SPV ⁡ ( λ 1 ) Φ eff ⁡ ( λ 1 ) ∝ L 2 L 2 - z 2 ⁡ [ ( z ⁢ S b D - 1 ) ⁢ ( cosh ⁡ [ T L ] - exp ⁡ [ - T z ] ) + ( z L - S b ⁢ L D ) ⁢ sinh ⁡ [ T L ] ] wherein S b is the velocity of the rear surface recombination, L is the diffusion length of the minority charge carriers, D is the diffusion constant of the minority charge carriers and T is the thickness of the semiconductor sample.