1. Introduction to Solids

2. 3 Classes of Solids Amorphous – No long range order Polycrystalline – Order within grains Single Crystal – Regular, repeated pattern

3. Crystal Solid Single crystal – repetition of a unit cell Crystal lattice – Array of corners of unit cells Symmetry – Used to classify the crystal – Ex. Cubic symmetry

4. 3 Subclasses of Cubic Crystals Simple – The sites for atoms are at the corners of the cubes Body-Centered-Cubic (bcc) – The sites for the atoms are at the corners of the cubes Face-Centered-Cubic (fcc) – The sites for the atoms are at the corners and at the centers of each face of the cube Note: Show figures

6. Crystal Structures Diamond structure Zincblende structure Knowing the crystal structure, chemical composition and density of material, the following can be calculated – the length of the side of the unit cell – distance between centers of nearest neighbor atoms Note: Show figures Structures of Si and GaAs

8. Crystal Structures X-ray diffraction – Method used to determine the plane and direction of a crystal The specification of particular planes and directions is made through the use of Miller indices

9. Finding Milles indices of a plane in a crystal – Choose coordinate access along the principal directions in the crystal (long the unit cell edges) – Take the 3 numbers that result as the intersection of a plane with the 3 axes Take their reciprocals Multiply the results by the smallest value that will give 3 integers These 3 integers are the Mille indices of the plane

10. Finding Milles indices of a direction in a crystal – Take the 3 components of a vector in that direction along the 3 axes – Multiply these components by whatever is needed to reduce them to the smallest set of integers – These integers are the Miller indices of the direction

11. Miller indices of a plane (101)  {101} Miller indices of a direction [101]  If negative, minus sign is placed over the integer

12. Two Types of Imperfections Defects – The ideal unit cell repetition is interrupted in some way Impurity – Occasional atoms of types other than the ones that make up the defined crystal’s unit cell. – Sometimes, intentionally introduced

13. Impurity Doping – adding impurities Dopant – the added material

14. Energy Level Single atoms – Only one electron can occupy a given state (Pauli exclusion principle) – Different states  different energies associated – Ground state  electrons of an atom are in the lowest possible energy states – Excited state  when an electron moves to the state of higher energy

15. Energy Level Nucleus  protons + neutrons

17. Energy Level Principal energy level 1 2 3 4 5 6 Sublevel 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g 6s 6p 6d 6f 6g 6h

18. Energy Level the 1s energy level is always the lowest energy level of all principal energy levels for each principal energy level, the s sublevel is also the lowest energy sublevel The diagram at the right illustrates the determination of order of sublevels by increasing energy Source: http://library.thinkquest.org/15567/lessons/2.html

19. Orbital A region within a sublevel where electrons may be found In each orbital, there can be a maximum of two electrons – Each s sublevel has a single orbital – Each p sublevel has 3 orbitals – Each d sublevel has 5 orbitals – Each f sublevel has 7 orbitals Thus, any s sublevel can have two electrons, while any p sublevel can have 6 electrons, and so on No. of sublevels No. of orbitals (s, p, d, f) Total No. of orbitals Maximum no. of electrons 12341234 (1) (1, 3) (1, 3, 5) (1, 3, 5, 7) 1 4 9 16 2 8 18 32

20. Band Gap Source: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html

21. Fermi-Level Extra levels have been added by the impurities In n-type material there are electron energy levels near the top of the band gap so that they can be easily excited into the conduction band In p-type material, extra holes in the band gap allow excitation of valence band electrons, leaving mobile holes in the valence band

22. Video Links CLASSES OF SOLIDS http://www.youtube.com/watch?v=SJsckwYxfgY&feature=related CRYSTAL LATTICE Lattice Structures Part 1 (Cubic, body-centered, Face centered --> unit cell) http://www.youtube.com/watch?v=Rm-i1c7zr6Q&feature=related SAND TO SILICON TO IC http://www.youtube.com/watch?v=Q5paWn7bFg4 SILICON RUN 1 http://www.youtube.com/watch?v=ATt5dwdKt9I