Semiconductor Physics 2

7/28/2019 Semiconductor Physics 2

1/29

11th April 2013

2nd Lecture

Semiconductor Physics / Micro and Nano


2/29

11th April 2013

2nd Lecture


Semiconductor

Intrinsic semiconductors

Extrinsic semiconductor

- dopants (impurities)

donor

acceptor

n-type (-)

p-type (+)

BandgapEg/eV


3/29

11th April 2013

2nd Lecture


Lecture 2

Energy

Wavelength

Frequency


4/29

11th April 2013

2nd Lecture


If a semiconductor does not have many impurity levels in theband gap, photons with energies smaller than the band gapenergy cannot be absorbed

There are no states with energies in the band gap

This explains why wide band gap semiconductors aretransparent to visible light, whereas narrow bandsemiconductors (Si, GaAs) are not

Example: Pure Diamond

Semiconductor

Energy gap

&

Optical pro pert ies


5/29

11th April 2013

2nd Lecture


Energy E / eV

1 eV = 1,60210-19 J1 kT = 0,025 eV (T = 300 K)1 nm = 10-9 m = 10

410 495 620 700

Wavelength / nm

560

3,0 2,5 2,2 2,05 1,7

UV IR


6/29

11th April 2013

2nd Lecture


Typical size of an atom: Radius 10-10 mThis can just be resolved by modern electron microscopes.

12 g of the Carbon isotope 12C contain 6,0221023 atoms.

Avogadro number NA = 6,0221023 .

A Diamond weighing 12 g amounts to 60 Karat(0,2 g 1 Karat) and has a volume of 3.5 cm.


7/2911th April 2013

2nd Lecture


Lecture 2

Once more..

http://www.corrosionsource.com/handbook/periodic/periodic_table.gif


8/2911th April 2013

2nd Lecture


Lecture 2


9/2911th April 2013

2nd Lecture


Semico nduc tors & Band Gap Examples

Type Elements Bandgap (Eg)

/eV

IV C 5.3

IV Si 1.1

IV Ge 0.7

IV SiC 2.8

(crystalline inorganic materials)


10/2911th April 2013

2nd Lecture


III-V Compound Semiconductors

(Periodic Table Columns III & V)

Column III Column V

B N

Al P

Ga As

In Sb

Tl not used Bi AlN (6.28), AlP (2.45), AlAs (2.15), AlSb (1.63)

GaN (3.44), GaP (2.27), GaAs (1.43), GaSb (0.70)

InN (0.77), InP (1.35), InAs (0.36), InSb (0.18)


11/2911th April 2013

2nd Lecture


II-VI Compound Semiconductors

(Periodic Table Columns II & VI)

Column II Column VI

Zn O

Cd SHg Se

Mn sometimes Te

not used Po ZnO (3.4), ZnS (3.68), ZnSe (2.7), ZnTe (2.26)

CdS (2.48), CdSe (1.75), CdTe (1.43)


12/2911th April 2013

2nd Lecture



13/2911th April 2013

2nd Lecture


Lecture 2 Symmetry and Notat ions

Crystal Structure long range order

the atoms are arranged in a lattice or array

well defined symmetry properties

Diamond & Zincblende

fcc

face centered cub ic


14/2911th April 2013

2nd Lecture


Primitive translations:

a,b,c

Translation:

clbmanR

Periodicity

1D

2D

3D

Periodicity:- Discrete translational symmetry

- Bravais lattice, or space lattice

n, m, l integers(n,m,l) Lattice point

0)( cba

Volume


15/2911th April 2013

2nd Lecture


Choice ofprimitive cell

- The primitive cell can be usedto reproduce the entire crystal

- The choice of unit cell isnot unique

-The smallest distancesbetween lattice points arethe lattice spacing


16/2911th April 2013

2nd Lecture


Basis = group of atoms forming the unit cell:

Basis

Crystal Structure

Lattice + Basis = Crystal structure

Lattice

Basis = group of atoms forming the unit cell:

Basis

Crystal Structure

Lattice + Basis = Crystal structure


17/2911th April 2013

2nd Lecture



18/29

11th April 2013

2nd Lecture


Crystal structure:

=lattice + basis

lattice generated by translating a direct lattice vector

basis The set of atoms which, when placed at each lattice point,generates the crystal structure.

clbmanR

R


19/29

11th April 2013

2nd Lecture


Crystal structure basic symmetry operations

E -Identity operation

Cn - n-foldrotationRotation by (2/n) radiansC2 = (180

), C3 = () (120), C4 = () (90

), C6 = ()

(60)

- Reflection symmetry through a plane

Sn - Cnrotation, followed by a reflection through aplane rotation axis


20/29

11th April 2013

2nd Lecture


Rotation

Cn - n-foldrotation

n=?

C6 = () (60)


21/29

11th April 2013

2nd Lecture


- Reflectionsymmetrythrough a plane


22/29

11th April 2013

2nd Lecture


Bravais lattices

unit cell primitive cell


23/29

11th April 2013

2nd Lecture


!


24/29

11th April 2013

2nd Lecture


fccbcc


25/29

11th April 2013

2nd Lecture


fccbcc

Primitive cells of fcc and bcc lattices


26/29

11th April 2013

2nd Lecture


Tetrahedral coordination

Si and Ge have diamond lattice (C)GaAs has a zincblende lattice

Diamond & Zincblende lattices two interpenetrating fccsublattices one displaced from the other by of thedistance along the diagonal of the cell (a3/4)


27/29

11th April 2013

2nd Lecture


Diamond & Zincblende lattices two interpenetrating fccsublattices one displaced from the other by of thedistance along the diagonal of the cell (a3/4)

http://jas.eng.buffalo.edu/education/solid/unitCell/home.html


28/29

11th April 2013

2nd Lecture


Miller Indices of Planes


29/29

11th A il 2013

2nd Lecture


Planes: (hkl)Directions: [hkl]

Distance of planes in the cubic system:

222lkh

adhkl

Miller Indices

Semiconductor Physics 2

Documents

Transcript of Semiconductor Physics 2