Measurement of Diffusion Lengths in Direct-Gap Semiconductors by Electron-Beam Excitation

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Abstract
In semiconductors having high efficiency for radiative recombination, the voltage dependence of cathodoluminescence may be used to determine the diffusion length and to estimate the surface recombination velocity of excess carriers. Theoretical calculations are based on a knowledge of the Laplace transform of the distribution of excitation with depth as determined from the target absorption correction in electron probe microanalysis or, alternatively, on a Gaussian approximation to the distribution of excitation with depth. Experimental results with accelerating voltages of 5–50 kV indicate values of diffusion length in n‐type GaAs ranging from 3.0 μ at low‐carrier concentration (5.1×1016 cm−3) to 0.65 μ at high‐carrier concentration (3×1018 cm−3). The estimated accuracy for diffusion lengths between 0.5 and 4 μ is ±30%. Information is also obtained on the surface recombination velocity and the thickness of a ``dead layer'' at the surface.