II-VI Semiconductor Materials, Devices, and Applications

II-VI Semiconductor Materials, Devices, and Applications
EE 4611Presenter: Lera BeletskyApril 11, 2016
Outline
MaterialsStructurePropertiesBandgap EngineeringApplicationsDevicesCurrent Research
Why II-VI?
Compounds
Any combination of:Cd, Zn, HgO, S, Se,TeMost commonly used:CdS,CdSe,CdTeZnO,ZnS,ZnSe,ZnTeCdOand mercury compounds of lesser interest
Structure
Zinc Blende (Sphalerite)
Wurtzite
http://som.web.cmu.edu/structures/S011-ZnS.html
http://som.web.cmu.edu/structures/S014-ZnO.html
Properties
Carrier concentration,etcHard to measureDependent on growthtechniqueBand gapsDirectWide band gap (>2eV) devices operate at higher:VoltagesFrequenciesTemperatures
Properties of ZnO
pH range: 6.95-7.37Non-toxicn-typeEasily wet etchedTransparent when doped with AlBand gap: 3.37eVAbsorbance ~380nmExcitonbinding energy:ZnO: 60meVGaN: 25meVEfficient operation at room temperature
https://en.wikipedia.org/wiki/Zinc_oxide
Bandgap Engineering
Changingbandgapwith dopingZnO: 3.37eVMgO:7.8eVWurtzite phaseMgZnOHighest Mg content: 55%Bandgap: 4.55eVBenefitsAbsorbance ~270nmRetains attractive ZnO properties
A.Ohtomoet al.MgZnOas a II-VIwidegapsemiconductor alloy.Appl. Phys.Lett.72, 2466,1988.
Applications
Solar cellsPhotoresistorsLasersBlue LEDs (ZnSereplaced byGaN)Tetrahertzimaging (ZnTe)LCD displaysGas sensorsZnO nanowire FETs
Solar Cells
http://www.auo.com/?sn=192&lang=en-US
CdTe/CdSSolar Cells
ProsThin filmEasy to makeLess expensive than SiBetter solar absorption profileDrawbacksEfficiency ~12-14% (c-Si ~13-20%)Toxicity
http://www.nrel.gov/pv/thinfilm.html
Gas Sensors
Sensing material on topElectrical resistance change via chemical reactionImportant featuresResponseGas selectivityVery low concentrations
http://www.nature.com/am/journal/v2/n2/full/am201040a.html
Nanostructures
Increased surface areaDecrease reflectionIncrease efficiencyGrowthCVDMOCVDMBEHydrothermal
http://spie.org/newsroom/technical-articles-archive/3261-antireflective-nanostructures-for-high-efficiency-optical-devices
ZnO Structures
http://www.hindawi.com/journals/apec/2012/834961/fig8/
http://www.nature.com/am/journal/2010/201008/full/am2010154a.html
Thin Film
Nanowires
ZnO-Based Gas Sensors
Regular thick film
Nanostructured film
Deore, M.K. and Jain, G.H. Synthesis,characterisationand gas sensing application ofnanoZnO material. Int. J. Nanoparticles.2014, 7, 57-72.
ZnO-Based Gas Sensors
% Selectivity = max response other gases: max response target gas
Deore, M.K. and Jain, G.H. Synthesis,characterisationand gas sensing application ofnanoZnO material. Int. J. Nanoparticles.2014, 7, 57-72.
Summary
Elements from the IIB (Cd, Zn, Hg) and VI (O, S, Se,Te) groupsElectrical properties are highly dependent on growth methodWide and direct band gapsLEDs, lasers,photoresistors, THz imaging, and LCD displaysCurrent researchNanostructuresSolar cellsGas sensors
References
SafaO.Kasap, Peter Capper (2006).Springer handbook of electronic and photonic materials. Springer. pp. 54,327. ISBN 0-387-26059-5.http://link.springer.com/chapter/10.1007%2F978-1-4615-5247-5_36A.Ohtomoet al.MgZnOas a II-VIwidegapsemiconductor alloy.Appl. Phys.Lett.72, 2466,1988.Manekkathodi, A., Lu, M-Y., Wang, C.W. & Chen, L.-J. Direct growth of aligned zinc oxidenanorodson paper substrates for low-cost flexible electronics.Adv. Mater.Publishedonline: 28 May 2010; doi:10.1002/adma.201001289.http://solarcellcentral.com/solar_page.htmlAfzaal, M. and O’Brien, P. Recent developments in II-VI and III-VI semiconductors and their applications in solar cells. J. Mater. Chem.,2006,16, 1597-1602.Springer Handbook of Electronic and Photonic Materials, ISBN 978-0-387-26059-4. Springer-VerlagUS, 2007, p. 325Deore, M.K. and Jain, G.H. Synthesis,characterisationand gas sensing application ofnanoZnO material. Int. J. Nanoparticles.2014, 7, 57-72.Fine, G.F.; Cavanagh, L.M.;Afonja, A.;Binions, R.; Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring.Sensors2010, 10, 5469-5502.http://spie.org/newsroom/technical-articles-archive/3261-antireflective-nanostructures-for-high-efficiency-optical-devices
Key Points
Wide and direct band gaps very useful for optoelectronicsBandgap engineering improves properties of ZnO while retaining its benefitsCdTe/CdSsolar cells are cheaper than Si (just need to increase efficiency)CdTe/CdSsolar cells cover more of the solar spectrum than c-SiGrowth of nanostructured materials like ZnO nanowires improves performance (i.e. gas sensing, solar reflection)