ece340Fall03HW2sol - ECE 340 Homework II Fall 2003 Due:...

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ECE 340 Homework II Fall 2003 Due: Wednesday, September 10, 2003 1. (a) An InP semiconductor crystal is doped with tin atoms. If the tin atoms displace indium atoms, does the crystal become an n-type or p-type material? Why? (b) For a nonstoichiometric GaAs whose crystal structure remains to be zinc-blende but its compositional ratio of As/Ga is slightly larger than 1, e.g. 1.005. Assume that the excess As atoms substitute for Ga, and the crystal contains no other impurities. Is this nonstoichiometric GaAs n-type or p-type? Why? Solutions: (a) n-type Reasoning: In has 3 covalent electrons. Tin (Sn) has 4 covalent electrons. Because tin atom has one more covalent electron than In atom, when it replaces In atom, it introduces a free electron. The Si atom becomes donor atom and the crystal becomes n-type. (b) n-type Reasoning: As has 5 covalent electrons. Ga has 3 covalent electrons in outer shell. When As substitutes for Ga, two electrons are introduced, resulting in n-type materials.
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ece340Fall03HW2sol - ECE 340 Homework II Fall 2003 Due:...

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