ENGRI111_HW3_2007 - ENGRI 111 Homework#3 Due Monday October...

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ENGRI 111 Homework #3 Due Monday October 1, 2007 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? 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? 3. A B&W photographic film contains silver halide particles embedded in a polymer. When the silver halide particles are illuminated by a light of sufficient energy, conduction band electrons and valence band holes are created. The electrons can move through the silver halide particle and they can combine with silver ions to form a neutral silver atom.
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