# HW 1 - EE 212 FALL 09-010 HOMEWORK ASSIGNMENT#1 ASSIGNED...

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EE 212 FALL 09-010 HOMEWORK ASSIGNMENT #1 ASSIGNED: THURSDAY SEPT. 24 DUE: THURSDAY OCT. 1 ANSWER SHEET Reading Assignment: Chapters 1 and 2 in the text. #1. Spend 30 min or so scanning the information in the 2007 ITRS Executive Summary (on the class website or at the website given in the class notes). You don’t need to turn anything in for this HW problem. The next two problems are meant to review some basic concepts of semiconductor materials. This material was not covered in class but is in Chapter 1 in the text. We will use these basic concepts throughout the quarter. #2. A silicon wafer is contaminated with gold atoms to a density of 10 15 cm -3 . Au atoms in silicon can act as either donors or acceptors. E D and E A levels exist for the Au and are both close to the middle of the silicon bandgap. Two regions on the wafer are also doped respectively with: i) 1x10 18 cm -3 Boron atoms ii) 5x10 17 cm -3 Arsenic atoms B As Au a) Determine the resistivity of each region at 300 K. You can use Fig. 1.18 in the text. Explain how the Au behaves in the N and P regions as part of your answer. Does it act as a donor or an acceptor? (5 points) b) Calculate the equilibrium electron and hole concentrations of each region at 300 K. (5 points). Answer: a) In N type material, the Fermi level will be in the upper half of the bandgap as shown in the band diagram below. Allowed energy levels below E F will in general be occupied by electrons. Thus the E D and E A levels will have electrons filling them. This means the donor level will not have donated its electron whereas the acceptor level will have accepted an electron. Thus the Au atoms will act as acceptors in N type material.

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Free Electrons Holes E F E D E A E C E V In P type material, the Fermi level will be in the lower half of the bandgap. Allowed energy levels above E F will in general not be occupied by electrons. Thus the E D and E A levels will not have electrons filling them. This means the donor level will have donated its electron whereas the acceptor level will have not accepted an electron. Thus the Au atoms will act as donors in P type material.
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## This note was uploaded on 06/12/2011 for the course EE 212 taught by Professor Plummer during the Fall '09 term at Stanford.

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HW 1 - EE 212 FALL 09-010 HOMEWORK ASSIGNMENT#1 ASSIGNED...

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