Electron-Beam Excited Minority-Carrier Diffusion Profiles in Semiconductors

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Abstract
It is shown that electron‐beam generation of minority carriers at a semiconductor surface can be used to establish as an exponential minority‐carrier diffusion profile Δp (z), measured along the z direction perpendicular to this surface, which is insensitive to possible variations in the surface recombination velocity. This profile can be expressed very simply, Δp (z) = C exp (−z/L), where L is the carrier diffusion length. On the basis of this result, a new measurement technique has been proposed, in which the induced junction current is measured as the electron beam is scanned along an angle‐lapped surface of a p‐n junction. For a small angle θ between the lapped surface and the junction, the induced current I varies exponentially with scan distance x, I = I0 exp (−x sin θ/L), and provides a direct and accurate determination of the carrier diffusion length L. This technique has been successfully utilized to measure diffusion lengths down to 0.2μ (with 10% accuracy) for GaP, and it should be useful for measuring very short diffusion lengths in other semiconductors.