Lecture_2

Lecture_2 - 1 Prof. J. S. Harris 1 EE243. Semiconductor...

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Unformatted text preview: 1 Prof. J. S. Harris 1 EE243. Semiconductor Optoelectronic Devices (Winter 2010) Crystals Compound semiconductors Bloch theorem Band structure and the Brillouin zone Effective mass approximation Kane band theory results Semiconductor statistical mechanics 1. Review of Basic Semiconductor Physics Prof. J. S. Harris 2 EE243. Semiconductor Optoelectronic Devices (Winter 2010) All materials in this course are crystalline semiconductors Crystal - a structure that can Fll all space based on the regular repetition of a particular unit cell Unit cell - unit to construct crystal by regular repetition • Primitive - smallest cell which will replicate the crystal • Cubic - Larger most commonly used as most semiconductors are diamond or zincblende structure, for which the primitive unit cell is complex and it ʼ s easier to visualize cubic replication Crystals 2 Prof. J. S. Harris 3 EE243. Semiconductor Optoelectronic Devices (Winter 2010) Unit cells for silicon (Si) and gallium arsenide (GaAs) Silicon- diamond lattice GaAs- zincblende (cubic zinc sulFde) lattice (most other III-V and many II-VI semiconductors have zincblende lattice) Diamond and zincblende lattices are based on tetragonal pattern of bonds from each atom to nearest neighbors-two interlocking face-centered-cubic lattices lattice parameter (or lattice constant), a- repeat length of the unit cells e. g., GaAs, a = 5.65 Å (Angstroms) = 0.565 nm. Diamond and Zincblende Lattices Prof. J. S. Harris 4 EE243. Semiconductor Optoelectronic Devices (Winter 2010) Wurtzite structure ¡ound in AlN, GaN, InN These materials have revolutionized short-wavelength light emitters (e. g., blue and green LEDs) Based on the same tetragonal set of bonds from each atom Wurtzite Lattice Two interlocking hexagonal- close-packed lattices of the two different (" dark" and "light") atoms. Note - Wurtzite has different symmetry properties (e. g., hexagonal, not cubic, hence x & y identical, but z (or c) is different, resulting in different band structures from zincblende materials 3 Prof. J. S. Harris 5 EE243. Semiconductor Optoelectronic Devices (Winter 2010) Silicon band structure. Note that the minimum in the conduction band is not directly above the maximum in the valence band, making silicon an indirect band gap semiconductor. GaAs band structure. Note that the highest energy in the valence bands (point marked Γ 8 ) is directly below the lowest energy in the conduction bands (point Γ 6 ), making GaAs a direct band gap semiconductor. Silicon and GaAs Band Structures Si GaAs Prof. J. S. Harris 6 EE243. Semiconductor Optoelectronic Devices (Winter 2010) Ge, An almost direct bandgap material Germanium GaAs 4 Prof. J. S. Harris 7 EE243. Semiconductor Optoelectronic Devices (Winter 2010) For optoelectronics, most devices are fabricated of “compound semiconductors” especially III-V materials made from Group III (Ga, In, Al) and Group V (As, P, Sb, N) elements Si and Ge (Group IV) are used sometimes as photodetectors...
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This note was uploaded on 06/05/2010 for the course EE 243 taught by Professor Harris,j during the Winter '10 term at Stanford.

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Lecture_2 - 1 Prof. J. S. Harris 1 EE243. Semiconductor...

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