Gallium Nitride (GaN)
PHYS 571
Gugun Gunardi
Heath Kersell
Damilola Daramola
Gallium Nitride (GaN)
 Introduction
 Properties
 Crystal
Structure
 Bonding Type
 Application
Introduction

The next important semiconductor
material after silicon.
http://www.phy.mtu.edu/yap/images/g
alliumnitride.jpg

Can be operated at high temperatures.

The key material for the next generation
of high frequency and high power
transistors.

Wide band gap energy.
Properties
PROPERTY / MATERIAL
.
Structure
Stability
Cubic (Beta) GaN
.
Zinc Blende
Meta-stable
Lattice Parameter(s) at 300K
0.450 nm
Density at 300K
Nature of Energy Gap Eg
6.10 g.cm-3
Direct
Energy Gap Eg at 293-1237 K
Hexagonal (Alpha) GaN
.
Wurzite
Stable
a0 = 0.3189 nm
c0 = 0.5185 nm
6.095 g.cm-3
Direct
3.556 - 9.9x10-4T2 /
(T+600) eV
Ching-Hua Su et al, 2002
Properties
3.44 eV
3.23 eV
Ramirez-Flores et al 1994
Energy Gap Eg at 300 K
.
3.25 eV
Logothetidis et al 1994
Monemar 1974
.
3.45 eV
Koide et al 1987
.
3.457 eV
Ching-Hua Su et al, 2002
Energy Gap Eg at ca. 0 K
3.30 eV
3.50 eV
Ramirez-Flores et al1994
Ploog et al 1995
Dingle et al 1971
Monemar 1974
Properties
Comparison between Common Semiconductor Material Properties and GaN
Hole Mobility
(cm2/Vs)
Critical Field Ec
(V/cm)
Thermal
Conductivity sT
(W/mK)
Coefficient of
Thermal
Expansion
(ppm/K)
Material
Bandgap (eV)
Electron
Mobility
(cm2/Vs)
InSb
0.17, D
77,000
850
1,000
18
5.37
InAs
0.354, D
44,000
500
40,000
27
4.52
GaSb
0.726, D
3,000
1,000
50,000
32
7.75
InP
1.344, D
5,400
200
500,000
68
4.6
GaAs
1.424, D
8500
400
400,000
55
5.73
GaN
3.44, D
900
10
3,000,000
110 (200 Film)
5.4-7.2
Ge
0.661, I
3,900
1,900
100,000
58
5.9
Si
1.12, I
1,400
450
300,000
130
2.6
GaP
2.26, I
250
150
1,000,000
110
4.65
SiC (3C, b)
2.36, I
300-900
10-30
1,300,000
700
2.77
SiC (6H, a)
2.86, I
330 - 400
75
2,400,000
700
5.12
SiC (4H, a)
3.25, I
700
3,180,000
700
5.12
C (diamond)
5.46-5.6, I
2,200
6,000,000
1,300
0.8
1,800
Crystal Structure

GaN grown in
◦ Wurtzite crystal structure
◦ Zinc-blende crystal structure
The band gap, Eg, effected by crystal
structure

Wurtzite
Crystal Structure
•Wurtzite crystal structure is a
member of the hexagonal crystal
system
•The structure is closely related to the
structure of hexagonal diamond.
• Energy gap: 3.4 eV
http://en.wikipedia.org/wiki/Image:
Wurtzite-unit-cell-3D-balls.png
Wurtzite
Crystal Structure

An ideal angle: 1090

Nearest neighbor: 19.5 nm

Energetically favorable

Several other compounds can take the wurtzite
structure, including Agl, ZnO, CdS, CdSe, and other
semiconductors.
Zinc-blende
Crystal Structure
• Energy gap 3.2 eV
• An ideal angle: 109.470
• Nearest neighbor: 19.5 nm
http://en.wikipedia.org/wiki/Image:Sphaleriteunit-cell-depth-fade-3D-balls.png
GaN Bonding Properties

Tetrahedral bonds
◦ sp3 hybridization
◦ Bonding angle: 109.47°
◦ Bond Length: 19.5 nm

Ga-N bonds significantly stronger than Ga-Ga
interactions (based on distance)
Ionicity
•GaN exhibits mixed ionic-covalent bonding
•Ionicity of a bond is the fraction fi of ionic character
compared to the fraction of fh of covalent character
•By Pauling’s definition
•Modern definition
•
is the ionicity phase angle
1http://www.bcpl.net/~kdrews/bonding/bonding2.html
GaN Bonding Properties
Based on calculations using both methods, typical values are
Compound
Pauling ionicity
Modern ionicity2
AlN
0.430
0.449
AlP
0.086
0.307
AlAs
0.061
0.274
GaN
0.387
0.500
GaP
0.061
0.327
GaAs
0.039
0.310
InN
0.345
0.578
InP
0.039
0.421
InAs
0.022
0.357
NaCl
0.668
> 0.9
C (Diamond)
0
0
Bond Character dependent on electronegativity
χN >> χP > χAs > χSb
2J.C.
Phillips, Bonds and Bands in Semiconductors 1973
GaN Bonding Properties
•
•
Bonding strength determines energy gap
size
Large band gap evidence of strong
bonding in GaN
• Strongly Ionic Compounds (also insulators)
LiF – 11eV; NaCl – 8.5eV; KBr – 7.5 eV
• Other III-V compounds
e.g. GaN
GaP
AlSb
InP
–
–
–
–
3.2 eV/3.4 eV
2.3 eV
1.5 eV
1.3 eV
Applications

Gallium Nitride Typical Applications:

New Kind of Nanotube

Laser diodes
 High-resolution Printings

Microwave radio-frequency power amplifiers

Solar Cells
New Kind of Nanotube
• Single Crystal Nanotubes
Fabricated
• Gallium Nitride nanotubes have
diameter between 30 – 200 nm
• Potential for mimicking ion
channels
GaN Laser Diode
Normally emit
ultraviolet radiation
 Indium doping allows
variation in band gap
size
 Band gap energies
range from 0.7eV –
3.4eV

http://www.lbl.gov/ScienceArticles/Archive/assets/images/2002/Dec17-2002/indium_LED.jpg
GaN Laser Diodes

Applications in:
◦ ‘Blu-Ray’ technology
◦ Laser Printing
http://www.aeropause.com/archives/Blu-raycover_plat.jpg
GaN Solar Cells
Indium doped (InGaN)
 Conversion of many wavelengths for
energy


Theoretical 70% maximum
conversion rate.
 Multiple layers attain higher efficiency.
 Need many layers to attain 70%

Lattice matching not an issue
GaN Solar Cells
Advantages:
 High heat capacity
 Resistant to effects of strong radiation
 High efficiency
Difficulties:
 Too many crystal layers create system damaging
stress
 Too expensive
References
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http://www.reade.com/Products/Nitrides/Gallium-Nitride-(GaN)Powder-&-Crystals.html
http://www.semiconductors.co.uk/nitrides.htm#GaN
http://www.onr.navy.mil/sci_tech/31/312/ncsr/materials/gan.asp
http://www.lbl.gov/Science-Articles/Archive/MSD-gallium-nitridenanotube.html
http://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrumsolar-cell.html
http://www.lbl.gov/Science-Articles/Archive/blue-light-diodes.html
http://www.ioffe.ru/SVA/NSM/Semicond/GaN/bandstr.html#Basic
http://nsr.mij.mrs.org/4S1/G6.3/article.pdf
http://nsr.mij.mrs.org/news/industapp97.html