Lifetime Measurements of Excess Carriers in Semiconductors

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Abstract
A technique is described whereby bulk carrier lifetimes in semiconductors can be measured over a wide range of injection level without making any electrical connections to the sample. The excess carriers are created by visible light and their distribution is measured by absorption of infrared radiation. The most important advantage of this technique is that the electric field term can be neglected in the continuity equation which describes the carrier distribution and the diffusion length can thus be determined directly. It appears that this technique may be used even in the presence of trapping. Some measurements are described for germanium where it is found that the carrier lifetime may increase or decrease with injection level. This is consistent with the Hall-Shockley-Read theory of carrier recombination.