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Unformatted text preview: MSE 262, Spring ‘09 Homework #3 Instructions: Due Thursday, March 12th, 2009. Turn in one solution per group and be sure to include the group letter, the names of the group members and their contributions. Show all the work in your solutions, including generated graphs and print outs of computer generated results. Please also staple solutions together. Problem 1: Intrinsic Properties a) Find the bandgap at 300K for the following materials: Si, Ge, GaAs, GaN. If the temperature is increased to 400K would you see an increase or decrease in the bandgaps? Why? Ge= .66eV Si = 1.1eV GaAs= 1.42 eV GaN= 3.4 eV As you increase the temperature, there would be more thermal energy giving the electrons more energy which allows it to break the bond easier This will in turn shrink the bandgap in the material. b) In 3 sentences or less explain why is it so hard to make a Silicon laser? Since Silicon is an indirect bandgap semiconductor it would need a phonon (lattice vibration) in order for the electron and hole to recombine to generate light. This is a much less inefficient and thus less frequent recombination process compared to a direct bandgap material. c) Knowing that GaAs has a much higher mobility than Silicon why is Silicon used so predominately in the IC industry? The two main reasons why Si is used in the IC industry is the ability to easily form a stable and good dielectric SiO 2 and the fact that Si is very abundant and cheap. d) Using a computer , plot F(E) (equation 4.18) from 02eV for the case of E F =1eV for three temperatures: 10K, 300K, and 1000K. Make sure you use enough data points to see the slope at 10K. e) Differentiate F(E) with respect to E and find the slopes of F(E) at E F for the three temperatures in part d. f) Assume that E F is at the midgap of Ge and Si at 300K. How many more times likely is it for an electron to occupy a state at the conduction band edge in Ge than in Si at room temperature? g) You excite a GaAs sample using a 330nm laser. What wavelength photon will the sample emit? What happens to the extra energy?...
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This note was uploaded on 09/30/2009 for the course MSE 2620 taught by Professor Malliaras during the Spring '09 term at Cornell.
 Spring '09
 MALLIARAS

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