ece340 - ECE 340 Homework II Due: Monday, January 30, 2004...

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ECE 340 Homework II Spring 2004 Due: Monday, January 30, 2004 (20 points total) 1. (a) A GaAs semiconductor crystal is doped with silicon atoms. If the silicon atoms displace Ga atoms, does the crystal become an n-type or p-type material? Why? (b) In contrast, when GaAs doped with carbon atoms, it tends to become p-type. Do the carbon atoms displace Ga or As atoms? (6 points) Solutions: (a) n-type materials Reasoning: Ga has 3 covalent electrons. Si has 4 covalent electrons. Because Si has one more covalent electron than Ga, when it replaces Ga atom, it introduces a free electron. The Si atom becomes donor atom and the crystal becomes n-type. (b) As atom Reasoning (optional): As has 5 covalent electrons. Ga has 3 covalent electrons in outer shell. When carbon substitutes As, a hole is introduced, resulting in p-type materials. On the other hand, if the carbon substitutes Ga, the crystal will become n- type. 2.
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ece340 - ECE 340 Homework II Due: Monday, January 30, 2004...

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