Photoconductance decay information

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Photoconductance decay or Photoconductivity decay (PCD or PC), is a non-destructive analytical technique used to measure the lifetime of minority charge carriers in a semiconductor, especially in silicon wafers.^[1] The technique studies the transient photoconductivity of a semiconductor sample during or after it is illuminated by a light pulse. Electron–hole pairs are first generated by the light pulse, and the photoconductivity of the sample declines as the carriers recombine.

PCD is an important characterisation step in determining the quality and expected performance of wafers before they are used to fabricate devices such as integrated circuits or solar cells. It is one of the most common methods of determining carrier lifetimes.^[2]

PCD uses a fast light source (e.g. a xenon flash lamp) to excite the test sample, causing free carriers to be generated. Excess carriers in the material cause it to become more conductive, and thus the number of excess carriers (${\displaystyle \Delta n}$) can be measured over time by measuring the material conductivity. Conductivity can be measured through non-contact methods, such as through microwave reflectance, or inductive or capacitive coupling.^[3] A higher effective lifetime of minority charge carriers indicate that they can remain mobile in the wafer for a long time period before undergoing recombination.