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EESM5200 (L2) Quiz 02

Multiple fill-in-the-blank

The following figure shows the electron and hole currents along the position at the n-side of a PN junction. In the figure, the depletion width is very small and not observable.  Assume the diffusion coefficient and diffusion length for holes and electrons are the same (i.e. Dp=Dn and Lp=Ln).  Also take kT/q=0.025V, the n-side doping concentration is ND=1x1016cm-3 and the forward voltage is 0.5V in this problem.  Calculate the following (up to 3 significant digits if the answer is not a round number): 1) What is the hole current at the edge of n-side depletion region in mA? [Fill in the blank], mA 2) What is the p-side doping concentration of the PN junction? [Fill in the blank], cm-3 3) What is the new total diode current in mA if the n-side doping is increased by 10 times? [Fill in the blank], mA  

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The problem presents three filled-in values for a PN junction scenario and asks you to justify each one step by step. We’ll address each blank in turn, deriving the result from the given data and typical semiconductor relations. 1) Hole current at the edge of the n-side depletion region (in mA) – expected value: 0.4 mA - Start by noting that the figure shows currents along the n-side, with electrons moving in one direction and holes in the opposite, near the depletion region edge on the n-side. Since the depletion width is very small and Dp = Dn, Lp = Ln, diffusion dominates the carrier transport near the edge when forward-biased. - Under forward bias (0.5 V) and given kT/q = 0.025 V, the diffusion current for holes into the n-region scales with the hole concentration gradient and the diffusion coefficient. With symmetric diffusion properties (Dp = Dn) and equal diffusion lengths, the hole current at the n-side edge is driven by the h......Login to view full explanation

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