Yuri Andrade Sylvester [email protected]ENGRI 111 – Nanotechnology September 7, 2004 HOMEWORK #1 1) When silicon (Si) forms a crystal lattice its atoms are covalently bonded on a tetrahedral shape, and since it only has 4 valence electrons there is a very negligible electron movement (conductivity) at room temperature. When a pure sample of Si is doped (insertion of impurities) with a small amount of Aluminum (Al), the crystal lattice that is formed possesses “holes.” These holes (relative positive charges) arise from the fact that Al only has 3 valence electrons, allowing the electrons from the surrounding Si atoms to fill them, and thus completing their octet. This movement itself leaves a hole in the adjacent Si atom, in what it is a repetitive process, making the Si sample increase its conductivity. It is relevant to mention that the electron movement occurs because the Al atoms want to reach an octet. When a sample of silicon is doped with an atom containing 3 electrons, an overall positive charge is produced (holes); this is called a p-type
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This homework help was uploaded on 02/03/2008 for the course ENGRI 1110 taught by Professor Giannelis during the Fall '07 term at Cornell.