Gallium Nitride (GaN) Gallium Nitride (GaN) PHYS 571 Gugun Gunardi Heath Kersell Damilola Daramola
Gallium Nitride (GaN)PHYS 571Gugun GunardiHeath KersellDamilola Daramola
Gallium Nitride (GaN)IntroductionPropertiesCrystal StructureBonding TypeApplication
IntroductionThe next important semiconductor material after silicon. Can be operated at high temperatures.The key material for the next generation of high frequency and high power transistors.Wide band gap energy.
http://www.phy.mtu.edu/yap/images/galliumnitride.jpg
Properties
PROPERTY / MATERIAL . Cubic (Beta) GaN . Hexagonal (Alpha) GaN . Structure Zinc Blende Wurzite Stability Meta-stable Stable Lattice Parameter(s) at 300K 0.450 nm a0 = 0.3189 nm c0 = 0.5185 nm Density at 300K 6.10 g.cm-3 6.095 g.cm-3Nature of Energy Gap Eg Direct Direct Energy Gap Eg at 293-1237 K 3.556 - 9.9x10-4T2 / (T+600) eV Ching-Hua Su et al, 2002
Properties
Energy Gap Eg at 300 K 3.23 eV Ramirez-Flores et al 1994 . 3.25 eV Logothetidis et al 1994 3.44 eV Monemar 1974 . 3.45 eV Koide et al 1987 . 3.457 eV Ching-Hua Su et al, 2002 Energy Gap Eg at ca. 0 K3.30 eV Ramirez-Flores et al1994 Ploog et al 1995 3.50 eV Dingle et al 1971 Monemar 1974
PropertiesComparison between Common Semiconductor Material Properties and GaN
Material Bandgap (eV) Electron Mobility (cm2/Vs) Hole Mobility (cm2/Vs) Critical Field Ec (V/cm) Thermal Conductivity sT (W/mK) Coefficient of Thermal Expansion (ppm/K) 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 1,800 6,000,000 1,300 0.8
Crystal StructureGaN grown in
Wurtzite crystal structure Zinc-blende crystal structureThe 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 StructureAn ideal angle: 1090Nearest neighbor: 19.5 nmEnergetically favorableSeveral other compounds can take the wurtzite structure, including Agl, ZnO, CdS, CdSe, and other semiconductors.
Zinc-blendeCrystal Structure Energy gap 3.2 eV An ideal angle: 109.470 Nearest neighbor: 19.5 nm
http://en.wikipedia.org/wiki/Image:Sphalerite-unit-cell-depth-fade-3D-balls.png
Tetrahedral bonds
sp3 hybridizationBonding angle: 109.47Bond Length: 19.5 nmGa-N bonds significantly stronger than Ga-Ga interactions (based on distance)
GaN Bonding Properties
IonicityGaN exhibits mixed ionic-covalent bondingIonicity of a bond is the fraction fi of ionic character compared to the fraction of fh of covalent characterBy Paulings definition
Modern definition is the ionicity phase angle
1http://www.bcpl.net/~kdrews/bonding/bonding2.html
GaN Bonding PropertiesBased on calculations using both methods, typical values are2J.C. Phillips, Bonds and Bands in Semiconductors 1973Bond Character dependent on electronegativityN >> P > As > Sb
CompoundPauling ionicityModern ionicity2AlN0.4300.449AlP0.0860.307AlAs0.0610.274GaN0.3870.500GaP0.0610.327GaAs0.0390.310InN0.3450.578InP0.0390.421InAs0.0220.357NaCl0.668> 0.9C (Diamond)00
GaN Bonding PropertiesBonding strength determines energy gap sizeLarge band gap evidence of strong bonding in GaNStrongly Ionic Compounds (also insulators)LiF 11eV; NaCl 8.5eV; KBr 7.5 eVOther III-V compoundse.g. GaN 3.2 eV/3.4 eV GaP 2.3 eV AlSb 1.5 eV InP 1.3 eV
ApplicationsGallium Nitride Typical Applications: New Kind of Nanotube
Laser diodes
High-resolution Printings
Microwave radio-frequency power amplifiers
Solar Cells
New Kind of NanotubeSingle Crystal Nanotubes Fabricated
Gallium Nitride nanotubes have diameter between 30 200 nm
Potential for mimicking ion channels
GaN Laser DiodeNormally emit ultraviolet radiationIndium doping allows variation in band gap sizeBand gap energies range from 0.7eV 3.4eV
http://www.lbl.gov/Science-Articles/Archive/assets/images/2002/Dec-17-2002/indium_LED.jpg
GaN Laser DiodesApplications in:
Blu-Ray technology
Laser Printing
http://www.aeropause.com/archives/Blu-ray-cover_plat.jpg
GaN Solar CellsIndium 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 CellsAdvantages:High heat capacityResistant to effects of strong radiationHigh efficiency
Difficulties:Too many crystal layers create system damaging stressToo expensive
Referenceshttp://www.reade.com/Products/Nitrides/Gallium-Nitride-(GaN)-Powder-&-Crystals.htmlhttp://www.semiconductors.co.uk/nitrides.htm#GaNhttp://www.onr.navy.mil/sci_tech/31/312/ncsr/materials/gan.asphttp://www.lbl.gov/Science-Articles/Archive/MSD-gallium-nitride-nanotube.htmlhttp://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrum-solar-cell.htmlhttp://www.lbl.gov/Science-Articles/Archive/blue-light-diodes.html http://www.ioffe.ru/SVA/NSM/Semicond/GaN/bandstr.html#Basichttp://nsr.mij.mrs.org/4S1/G6.3/article.pdfhttp://nsr.mij.mrs.org/news/industapp97.html