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Quiz1Review - Semiconductor Crytals Semiconductor crystals...

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Semiconductor Crytals: Semiconductor crystals are composed of atoms from column IV, III & V, or column II & VI Most commonly used is Si b/c it readily grows a insulating thermal oxide (Si02) Properties and Growth 3 basic solid types: Crystalline (ordered) diamond Amorphous (disordered) window glass Polycrystalline (single crystallines ordered together randomly) polysilicon Crystal: periodic array of atoms Structure described by: Bravais lattice – periodic array of points Defined by a set of ‘translation vectors’ Unit Cell – shape can be translated via translation vectors to fill volume (Cannot be rotated) Will contain a net of one lattice point and one atomic basis set Atomic basis- fixed array of one or more atoms assoc. with each b.lattice If structure cannot be reproduced using smaller atomic basis called primitive Cubic lattice types: Simple cubic Body-centered cubic Face-centered cubic primitive lattice of most semiconductors Diamond and Zincblende have a fcc primitive lattice with a two atom basis Diamond: two atoms are same type Si, or Ge (column IV) Zincblende: two atoms are different types GaAs or AlAs (column III, V) Atom is bonded to its four nearest neighbors is a tetrahedral arrangement -can also be described with a sc lattice with eight atom basis For all cubic lattices- there are 48 equivalent directions (6 permutations based on order * 8 based on sign) Except in case where coordinate coefficients are the same or zero Miller Indices: Direction: e Write the direction vector r in terms of the lattice translation/basis vectors r = p a 1 + q a 2 + s a 3 r Scale p, q, and s via a positive number to obtain the smallest set of integers that have the same ratio to each other, h, k and l. (Find and multiply by smallest common denominator, or divide by largest common factor.)
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use [] for parallel directions, and <> for equivalent direction Planes: take the reciprocals of P, Q and S to obtain p, q and s , respectively: p = 1/ P, q = 1/ Q and s = 1/ S . r Scale p, q, and s to obtain the smallest set of integers that have the same ratio to each other, h, k and l (usually). Use () for parallel planes, and {} for equivalent plane For sc [hkn] is normal to (hkn) Planes: Bulk Crystal Growth: Need for high purity and large semiconductor crystals Obtaining large metal ingot (high purity semiconductor crystal) Czolchralski method: using single seed crystal, large ingot grown, and then pulled from it melt
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  • Spring '08
  • Banjeree
  • Condensed matter physics, valence band, Fermi level, majority carrier concentration, primitive Cubic lattice

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