hw3_solutions - ENGRI 111 Homework#3 Solutions 1 The color...

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

View Full Document Right Arrow Icon
ENGRI 111 Homework #3 Solutions 1. The color emitted from an LED is roughly its band-gap energy. What composition, if any, of GaP x A 1-x (see Figure below) would you use to make an LED that emits red (1.7 eV), yellow (2.1 eV) or green (2.3 eV). Can a blue (2.8 eV) LED be made from this family of solids? Why or why not? a) x = 0.25 for red (GaP 0.25 As 0.75 OR Ga 4 PAs 3 ), x = 0.75 for yellow (GaP 0.75 As 0.25 OR Ga 3 P 4 As) , and x= 1.0 for green (GaP) b) A blue LED cannot be made with a band gap of 2.8 eV because given this family of solids, the unit cell cannot be made small enough. There is an inverse relationship between bond length (unit cell) and band gap. A small unit cell has stronger bonds and stronger bonds lead to a larger band gap. 2. A solid has a completely filled lower energy band and a partially filled higher energy band. a) Predict the electrical properties of this solid on the basis of its band diagram. b) What would happen to the electrical properties of this solid if all of the electrons were removed from the conduction band and why? c) In chemical language is this an oxidation or a reduction process? a) A solid that has a completely filled valence band and a partially filled conduction band would have electrical properties similar to that of a metal where movement of
Image of page 1

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

View Full Document Right Arrow Icon
electrons is easy throughout the conduction band. The partially filled conduction band has energy levels that are separated by very small steps (10 -23 eV) that electrons can traverse with thermal energy. The mobility of these electrons gives the solid electrical properties of a conductor. b) If all the electrons were removed from the conduction band the conductivity of the material would drop dramatically. The removal of these electrons would leave the material with a full valence band and an empty conduction band. Depending on the size of the bandgap, this material would behave like a semiconductor or an insulator.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ 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