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# hw11_new - voltage At what forward voltage do the bands...

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ECE 440 Homework 11 Fall 2009 Due: Friday, Nov 20, 2009 1. Illuminated Diode. A silicon p-n diode with reverse saturation current 10 -10 A is used as photodiode. This diode is illuminated with sunlight, yielding a photocurrent of 1 mA. Find the maximum power (P m ) which can be generated by this diode (in the 4th quadrant, as in Fig. 8-3 of the textbook), and calculate the corresponding voltage (V m ) and current (I m ). 2. P-N junction Simulation. In the following exercise we will revisit the problem 3 of HW 10 and use the pn junction tools found in the following link: http://nanohub.org/resources/5120 Consider a Si sample maintained at equilibrium and room temperature with a p-side doping of N A = 10 17 /cm 3 and an n-side doping of N D = 5 × 10 17 /cm 3 . Keep all other parameters on the nanoHUB to their default values unless otherwise stated. I) Use the ‘PN Junction Exact Solution’ and view the Energy band diagram as a function of bias
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Unformatted text preview: voltage . At what forward voltage do the bands become flat? Plot the band diagram at V = 1 Volt, and explain the shape of the bands. II) For a long diode, the excess carrier concentration are given by equations (5-31a) and (5-31b) Use the ‘PN Junction Long Base Depletion Approximation’ and plot the peak of excess electron and hole concentration vs. V app . At what voltage do you begin to see high-level injection? III) Theoretical Exercise: a. Explain qualitatively how a forward bias across a pn junction reduces the width of the depletion region. b. For the pn junction considered in this problem, deep in the p-region is the current carried exclusively by electrons or holes? For such case, is the current dominated by drift, diffusion, or both? Justify your answer....
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