MidtemPrelim_2008_Keyl - MIDTERM EXAM ENGRI 1110...

Info icon This preview shows pages 1–3. Sign up to view the full content.

MIDTERM EXAM Name__________________________ ENGRI 1110 NANOTECHNOLOGY Oct. 16, 2008 Your exam should have 7 pages. You will have 1.5 hours to complete the exam. If you need extra space, please write on the other side of the page. PUT YOUR NAME ON EACH PAGE! You will not be penalized if you do not evaluate equations to get a numerical answer. However make sure your work is written neatly. You may use a 4-function or scientific calculator, but no graphing calculators are allowed. Suggestions for how to structure your answers: Write simple and concise answers Some answers only require a single word or number Some answers only require a well labeled diagram Semiconductors 1. a) Rank the following from smallest in energy to largest in energy (3 pts): i) Energy difference between the highest energy level of the valence band and the lowest energy level of the conduction band of Si ii) Energy difference between two adjacent electron energy levels within the valence band of Si iii) Energy difference between the energy level of a donor impurity and the lowest energy level of the conduction band of Si Smallest to largest: ii < iii < i b) Assign a value in eV to the three energies above (3 pts) i = ~1.1eV ii = ~10 -23 eV iii = ~0.03ev (answers within a factor of two correct) 2.P-n Junction a) (6 pts) Draw a schematic of a p-n junction. Using the symbol “h” for holes, “e” for electrons. “-“ and “+” for the charges that are not mobile, show the location of holes, electrons and all other charges for the p-n junction in equilibrium Page 1 of 8
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

MIDTERM EXAM Name__________________________ ENGRI 1110 NANOTECHNOLOGY Oct. 16, 2008 b) In a sketch you draw below, draw both: i) the electron energy levels for the p-n junction in equilibrium and ii) the electron energy levels for the p-n junction in the condition of reverse bias (8 pts total) Left is i) Right is ii) c) (5 pts) The color of light emitted by a light emitting diode will depend on the size of the band gap of the diode material. Explain why. LEDs function by radiative recombination of an electron and hole. The electron comes from the bottom of the conduction band, while the hole comes from the top of the valence band. Thus the light emitted has the energy of the band gap. The color of the light (if it’s in the visible spectrum) is a direct result of what the energy value is in eV or wavelength in nm. d) (3 pts) Give one example of a compound semiconductor used in light emitting diodes: _________ GaAs _____________ (many possibilities here) 3a). Germanium (Ge) is a semiconductor and being a Group IV element, behaves much like Si. It has a bandgap of 0.67 eV. I have an infrared-camera that is only sensitive to light less than 0.1 eV in energy. The camera is damaged if light greater than 0.8 eV is transmitted into it. I can put either a coating of Ge or a coating of Si on the outer entrance lense of this infrared camera so that the light passes through the coating before it reaches the camera. Which is a better choice, Ge or Si, and why? (4 pts) Ge is better because it will absorb light energies of 0.67eV and higher, while Si will only start absorbing at 1.1 eV. So the Ge coating will protect better as it will absorb any light greater than
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.
  • '09
  • UMBACH
  • MIDTERM EXAM ENGRI, semiconducting p-n junction

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern