Physics of Semiconductor Devices

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Diffusion current

The phosphorous concentration in a region of a silicon crystal varies linearly from a concentration of 40000000000000000 cm-3 at x = 0 to a concentration of 600000000000000000 cm-3 at x = 1 mm. The diffusion constant for electrons is 22.5 cm²/s, the diffusion constant for holes is 5.2 cm²/s, and the temperature is 300 K. What is the diffusion current density in the positive x-direction?

J = A/cm²