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Chapter 3:
Dark Current Considerations
The dark current density in any minority carrier detector architecture is determined by the thermal generation rate per unit volume, Jd ¼ qGtht ¼ qNmint/t, where Nmin is the equilibrium density of minority carriers in the detector volume under consideration, and t is the associated minority carrier lifetime. t is the dimension of the volume, which, in a well-designed detector, is both <Ld, the minority carrier diffusion length, and <1/a, where a is the absorption coefficient of the material. The density of minority carriers at any specific temperature is directly related to the bandgap of the material and, as such, is not a large differentiator between the various materials technologies available. The minority carrier lifetime is of much greater significance in defining the magnitude of the limiting dark current in any specific architecture, and the important lifetime mechanisms involved in IR semiconductors are now discussed.
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