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03_exam1fall

# 03_exam1fall - Page 1 of 8 YOUR NAME Department of...

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Page 1 of 8 YOUR NAME________________________________ Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 6.012 Electronic Devices and Circuits Exam No. 1 Notes: 1. Unless otherwise indicated, assume room temperature and that kT/q is 0.025 V. You may also approximate [(kT/q) ln 10] as 0.06 V. 2. Closed book; one sheet (2 pages) of notes permitted (to be handed with exam). 3. All of your answers and any relevant work must appear on these pages. Any additional paper you hand in will not be graded. 4. Make reasonable approximations and assumptions. State and justify any such assumptions and approximations you do make. 5. Be careful to include the correct units with your answers when appropriate. 6. Be certain that you have all eight (8) pages of this exam booklet and the formula sheet, and make certain that you write your name at the top of this page in the space provided. 6.012 Staff Use Only PROBLEM 1 (out of a possible 35) PROBLEM 2 (out of a possible 30) PROBLEM 3 (out of a possible 35) TOTAL

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Your name Page 2 of 8 Problem 1 - (35 points) -3 This problem concerns a specimen of gallium arsenide, GaAs, which has 2 x 10 16 cm donors and an unknown number of acceptors. A measurement is made on the specimen and it is found that it is p-type with an -3 equilibrium hole concentration, p o , of 5 x 10 17 cm . At room temperature in GaAs, the intrinsic carrier concentration, n i , is 10 7 cm -3 , the hole mobility, µ h , is 300 cm 2 /V-s, and the electron mobility, µ e , is 4000 cm 2 /V-s. The minority carrier lifetime, t min , is 10 -9 s. a) [6 pts] What is the net acceptor concentration, N A (= N a - N d ), in this sample, and what is the total acceptor concentration, N a ? -3 N A = cm -3 N = cm a b) [4 pts] What is the equilibrium electron concentration, n o , in this sample at room temperature?
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• Fall '03