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Physics of Semiconductor Devices |
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Diffusion current(a) The phosphorous (donor) concentration in a region of a silicon crystal varies linearly from a concentration of 1014 cm-3 at x = 0 to a concentration of 1017 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? (b) Plot (approximately) the current density versus electric field for silicon. How can the mobility be determined from this plot? The electron drift velocity saturates at fields above about 1000 V/cm. Why? |