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ECE 305 Exam 2: Semiconductor Physics - Spring 2015, Exams of Physics of semiconductor devices

Purdue University Physics of semiconductor devices

The second exam for ece 305 (electronic properties of materials) from spring 2015, taught by mark lundstrom at purdue university. It includes multiple-choice questions and problems related to semiconductor physics, covering topics such as diffusion, scattering mechanisms, low-level injection, and energy band diagrams. The exam also tests the understanding of minority carrier diffusion equations and their application in n-type semiconductors. It provides a comprehensive assessment of students' knowledge in semiconductor device physics.

Typology: Exams

2017/2018

Uploaded on 10/25/2025

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ECE#305' ' Spring'2015'

1'

NAME:______________________________________' ' PUID:':______________________________________'

'

ECE'305'Exam'2:'Spring'2015'

February'13,'2015'

Mark'Lundstrom'

Purdue'University'

'

This'is'a'closed'book'exam.''You'may'use'a'calculator'and'the'formula'sheet'at'the'end'of'

this'exam.''Following'the'ECE'policy,'the'calculator'must'be'a'Texas'Instruments'TI#30X'

IIS'scientific'calculator.'

'

There'are'three'equally'weighted'questions.''To'receive'full'credit,'you'must'show'your'

work'(scratch'paper'is'attached).'

'

The'exam'is'designed'to'be'taken'in'50'minutes.'

'

Be'sure'to'fill'in'your'name'and'Purdue'student'ID'at'the'top'of'the'page.'

'

DO'NOT'open'the'exam'until'told'to'do'so,'and'stop'working'immediately'when'time'is'

called.'

'

The'last'page'is'an'equation'sheet,'which'you'may'remove,'if'you'want.'

'

75'points'possible,'10'per'question'

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1)' 25'points'(5'point'per'part)'

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2)' 25'points'(5'points'per'part)'

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3)' 25'points'(5'points'per'part)'

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#########################'Course'policy''#########################'

'

I'understand'that'if'I'am'caught'cheating''in'this'course,'I'will'earn'an'F'for'the'course'and'

be'reported'to'the'Dean'of'Students.'

'

Read'and'understood:' ______________________________________________'

''''''signature'

Discover Exams of Physics of semiconductor devices Purdue University

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NAME: PUID: :

ECE 305 Exam 2 : Spring 2015 February 13, 201 5 Mark Lundstrom Purdue University This is a closed book exam. You may use a calculator and the formula sheet at the end of this exam. Following the ECE policy, the calculator must be a Texas Instruments TI-‐30X IIS scientific calculator. There are three equally weighted questions. To receive full credit, you must show your work (scratch paper is attached). The exam is designed to be taken in 50 minutes. Be sure to fill in your name and Purdue student ID at the top of the page. DO NOT open the exam until told to do so, and stop working immediately when time is called. The last page is an equation sheet, which you may remove, if you want. 75 points possible, 10 per question 1 ) 25 points (5 point per part) 2 ) 25 points (5 points per part) 3 ) 25 points (5 points per part) -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ Course policy -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ I understand that if I am caught cheating in this course, I will earn an F for the course and be reported to the Dean of Students. Read and understood: ______________________________________________ signature

Exam 1 : ECE 305 Spring 2015 Answer the five multiple choice questions below by drawing a circle around the one, best answer. 1a) Consider holes diffusing down a concentration gradient. What force pushes them down? a) + q E b) − q E c) +^ Dp dp^ dx d) − Dp dp dx e) none of the above 1b) For a semiconductor in equilibrium at very low temperatures, what is the most important scattering mechanism? a) Lattice scattering. b) Ionized impurity scattering. c) Auger scattering. d) Impact ionization scattering. e) Polar optical phonon scattering. 1c) Which of the following is a statement of “low-‐level injection” in a p-‐type semiconductor? a) ND << N (^) A. b) N (^) A << ND. c) p 0 << N (^) A. d) Δ n << N (^) A. e) Δ p << ni. 1d) To write the steady-‐state, minority carrier diffusion equation for a p-‐type semiconductor of length, W , as d^2 Δ np dx^2 = 0 , which one of the following must be true of the diffusion length, Ln? a) Ln << W. b) Ln >> W. c) Ln = W. d) Ln <<^ Lp. e) There is no restriction on Ln.

Exam Solutions: ECE 305 Spring 2015 2c) Sketch the electrostatic potential vs. position. Assume that V = 0 for x >> x 2. Make your sketch as accurate as possible without putting numbers on the vertical axis. 2d) Sketch the electric field vs. position. Make your sketch as accurate as possible without putting numbers on the vertical axis.

2e) Sketch the electron density, log ⎡ ⎣ n ( x )⎤ ⎦ vs. position. Make your sketch as accurate as

possible without putting numbers on the vertical axis.

Exam Solutions: ECE 305 Spring 2015

This problem concerns an n-‐type semiconductor at room temperature, in steady-‐ state and low level injection with no optical generation. The hole mobility is μ p = 500 cm^2 V-s for 0 ≤ x ≤ 5 μm and μ p = 50 cm^2 V-s for 5 ≤ x ≤ 10 μm. The minority hole lifetime is τ (^) p = 10 −^4 s. The excess hole densities at left and right ends in

the figure below are Δ p ( x = 0 ) = 1014 cm-^3 and Δ p ( x = 10 μm) = 0. Answer the

following questions. 3a) Simplify the general minority carrier diffusion equation for 0 ≤ x ≤ 5 μm. You must show your work and explain how you get your answer. Draw a box around your answer. You do not need to solve the equation. 3b) Simplify the general minority carrier diffusion equation for 5 ≤ x ≤ 10 μm. You must show your work and explain how you get your answer. Draw a box around your answer. You do not need to solve the equation.