EEE2045F: Tutorial 1
Jarryd Son
Instructions: This tutorial relates closely to Chapter 1 of Electronic Devices by Thomas
Floyd. Please answer the following questions in detail. Use diagrams and mathematical
formulae to elaborate your answers wherever applicable. These tutorials are to help you
consolidate the material covered in lectures.
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Semiconductor Physics
1. (a) Draw the energy diagrams for insulators, semiconductors and conductors. Clearly indicate the
conduction and valence bands as well as any band gaps of overlaps.
(b) Explain why semiconductors have conduction electrons at room temperature whereas insulators do
not. You can refer to the energy diagrams to assist your explanation.
(c) Explain why we would not typically use pure semiconductor materials to replace conductors in a
circuit.
(d) Do conductors have ‘holes’ as charge carriers? Explain your answer.
2. (a) What is doping (in the context of semiconductors) and why do we use it?
(b) What kind of impurities (trivalent/quadrivalent/pentavalent) are added to a pure semiconductor
to produce a P-type material?
i. Draw a diagram of how one atom of such an impurity is bonded to four silicon atoms. You
only need to indicate the valence shells for each atom and the associated electrons/holes as
necessary.
(c) How are minority charge carriers created in a doped semiconductor? And why are they considered
the minority?
(d) What are the minority charge carriers for P-type material?
3. (a) What causes negative ions to form when P and N-type semiconductors are joined together?
(b) On which side of a PN junction (P or N) are these negative ions formed?
(c) Draw the energy diagram for a PN junction after it has reached equilibrium. Clearly draw the
charge carriers present in each region and appropriate energy bands.
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