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Understanding Crystal Structure of Solids & Semiconductors in PHYS 3313 - Prof. Yin Guo, Study notes of Physics

An overview of the phys 3313 semiconductor physics course offered at oklahoma state university. The basics of semiconductors, their crystal structures, and the different types of solids. It also discusses the concept of lattice structures, unit cells, and crystal planes, as well as the different types of atomic bonding. Essential for students enrolled in the phys 3313 course, as it serves as a valuable resource for understanding the fundamental concepts of semiconductor physics.

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Uploaded on 11/08/2009

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PHYS 3313 SEMICONDUCTOR PHYSICS
Course Website:
http://physicscourses.okstate.edu/yguo/index.html
syllabus, lecture notes, homework solutions
What are semiconductors?
Materials with electrical conductivities between
those of insulators and conductors.
Examples: Si, Ge, GaAs
Energy band pictures of conductors,
insulators, and semiconductors:
Semiconductor devices:
Transistors, switches, diodes, detectors, etc
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Download Understanding Crystal Structure of Solids & Semiconductors in PHYS 3313 - Prof. Yin Guo and more Study notes Physics in PDF only on Docsity!

PHYS 3313 SEMICONDUCTOR PHYSICS

Course Website: http://physicscourses.okstate.edu/yguo/index.html

syllabus, lecture notes, homework solutions

What are semiconductors?

Materials with electrical conductivities between those of insulators and conductors. Examples: Si, Ge, GaAs

Energy band pictures of conductors, insulators, and semiconductors:

Semiconductor devices: Transistors, switches, diodes, detectors, etc

Overview of the Course:

Ch.1: The crystal structure of solids Describing crystal structure of solids

Ch.2: Introduction to quantum mechanics

  • Wave-particle duality
  • Discrete energy levels
  • Schrodinger’s equation

Ch.3: Introduction to the quantum theory of solids

  • Energy bands
  • Concept of the hole
  • Statistical mechanics

Ch.4: The semiconductor in equilibrium

  • Statistics of p type and n type semiconductors

Ch.5: Carrier transport phenomena

Ch.6: Nonequilibrium excess carriers in semiconductors

Ch.7: The pn junction

Ch.8: The pn junction diode

1.2 Types of Solids

Three general types:

1. Amorphous- with order only within a few atomic and molecular dimensions 2. Single crystal- with geometric periodicity throughout the entire material

  1. Polycrystalline- with multiple single-crystal regions (called grains) separated by grain boundary

Fig. 1.

1.3 Space lattices

Lattice: a regular periodic array of lattice points in space to represent the structure of a single crystal Lattice point: a structural unit repeated periodically to form the lattice

Example: Fig. 1.

1.3.1 Primitive and unit cell

Unit cell : a small volume that can be repeated to fill (form) the entire crystal

Primitive unit cell : the smallest unit cell. There is one lattice point per cell.

A unit cell is not unique for a given crystal.

Example: Fig. 1.

1.3.2 Basic crystal structures

Three common types:

  • Simple cubic
  • Body-centered cubic (bcc)
  • Face-centered cubic (fcc)

Fig. 1.5: structure and conventional unit cells of simple cubic, bcc, and fcc lattice. Volume of the unit cell=a^3 , a=lattice constant (edge of the cell)

Question: What are the number of atoms per unit cell in a simple cubic, bcc, and fcc lattice?

E1.1 The lattice constant of a fcc structure is a=4.75Å. What is the volume density of atoms?

Prob. 1.3(a) Assume that each atom is a hard sphere with the surface of each atom in contact with the surface of its nearest neighbor. Determine the percentage of total unit cell volume that is occupied in a simple cubic lattice.

Knowing the indices (hkl), one can determine:

  • The distance between parallel planes
  • Surface concentration of atoms

E1.3 Determine the distance between nearest (110) planes in a simple cubic lattice with a lattice constant of a 0 =4.83 Å (Ans: 3.42 Å)

E1.4 The lattice constant of a fcc structure is 4.75 Å. Calculate the surface density of atoms for (a) a (100) plane and (b) a (110) plane

1.3.4 The diamond structure

  • Two fcc structures displaced from each other along the body diagonal by one-fourth of its length (Fig. 1.10)

Figure 1.

The zincblende structure: two different types of atoms in the lattice. Example: compound semiconductors such as GaAs Fig. 1.

Figure 1.

1.4 Atomic bonding

What holds a crystal together?

The attractive electrostatic interaction between electrons and nuclei.

Why one particular crystal structure is favored over another for a given type of atoms?

Total energy of the system tends to reach a minimum value.

Thus, the crystal structure is closed related to atomic interactions/bonding.

1.5 Imperfections and impurities in solids

1.5.1 Imperfections in solids

Point defects:

  • Vacancy - a missing atom (Fig. 1.17(a))
  • Interstitial - an extra atom (Fig. 1.17(b))

Line dislocation- a row of atoms missing (Fig. 1.18)

1.5.2 Impurities in solids

  • Substitutional impurities – located at normal lattice sites (Fig. 1.19(a))
  • Interstitial impurities – located between normal sites (Fig. 1.19(b))

Doping: adding impurities to change conductivity of the semiconductor material.