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International Journal of Science Education
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electrons and holes. 
 
Figure 2. Generation of an electron-hole pair. 
Assuming that the students already have in mind that a material is a good conductor if it has many free 
electrons, it is hoped that they understand that the generation of many electron-hole pairs converts the 
semiconductor into a good conductor of electricity. It is necessary to insist that this situation occurs at high 
temperatures —to give them specific data, they can be told that Si begins to be a good conductor at 600K. In 
this context, a brief reference is made to the application of semiconductors in the generation of photovoltaic 
energy. Our intention here is for the students to acquire a basic idea of the application, understanding that 
sunlight provides the ionization energy necessary to release electrons from the covalent structure, and that 
these can then form part of an electrical current.
An example of question used to analyze the influence of 
temperature on the electrical behaviour of semiconductors is set next: 
A team of scientists has been asked to study how the variation of temperature [T] affects the electrical conduction of 
a conductor [Cu] and a semiconductor [Si]. To this end, they measured how the resistivity [ρ] of the two materials 
varied with temperature. The results were represented qualitatively by the two graphs of Figure A. Now you try to 
interpret those results by answering the following questions: 
a) How does the capacity to conduct electricity of Cu and of Si vary with temperature? 
b) Which of the two substances conducts electricity better at high temperatures? Why? 
c) In view of how the electrical conductivity of semiconductors varies with temperature, what applications might 
these materials have? 
Figure A. Variation of resistivity with temperature: (a) sample of Cu, (b) sample of Si 

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