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