Crystas and Crysta GrowngWhy Snge CrystasWhat s a snge crysta?Snge crystas cost a ot of money.When and why s the cost |usted?Current semconductor devces on an IC have characterstc dmensons of V mcron.What happens f gran sze s on the scae of mcrons?What makes optca materas ook transucent?What happens when a "weapons grade aser beam" hts an nhomogenety n an optca component?Appcatons of Snge CrystasFor what applications are single crystals necessary? 1. Semiconductor optoelectronics (substrate materials)Transistors, diodes, integrated circuits Si, !e, !a"s, #n$%&'s and lasers !a"s, !a#n"s, !a#n$, !a"s$, !a$(, rubySolar cells Si, !a"s, !a#n$)!a"s tandems*icrowa+e sources !a"s,. (on-glass optics (see pre+ious lecture .or transmission ranges) al/ali halides, al/aline earth halides, thallium halides, !e, sapphire0. &lectromechanical transducers1ltrasonic generators, sonar "'$, 2'$Strain gauges Si3ptical modulators %i(b30, 4aTi30, 4a(a(i30$ie5oelectric microphone sources 6uart57. 8adiation detectors 9g#,, (a#Tl, :s#Tl, %i#&u, Si, !e, ###-;, ##-;#, $bShy are they necessary .or those applications?((umbers correspond) 1. &lectrical homogeneity on the length scale o. the de+iceA minimum carrier scattering,. 3ptical homogeneity on the length scale o. the light being transmittedA minimum light scattering0. *echanical strength and homogeneityA a+ailability o. processing technology nic/el-based super alloy turbine blades7. $urityA well-de.ined material #n all cases optical, electronic or mechanical properties superior to non-single crystal competition.Superconductng Ceramc Snge CrystasAps.orgBuk Crysta Growth TechnquesTechnique Examples Advantages DisadvantagesMet: "Drectona Sodcaton"Eementa & Compound semconductors: S, Ge, GaAs, InP FASTLarge szes possbeOften energy ntensvesome materas decompose before metngBrdgman(horzonta/vertca)CuInSe2, MCT, CdTe, ZnSe, GaSe Oxdes-nsuators: sapphreReasonabe KehSeeded: predetermned orentatonCrucbe can be a probemCzochrask ("Cz")Wndows: sapphreScntators: BGO, CdWO4NLO materas: LNbO3, CsLB6O10Aka scntators-CsI:THades: wndows-wde transmttng tersAways the technque of choceDopants can be voate ContamnatonTechnique Examples Advantages DisadvantagesVapor Physca vapor transport(evaporaton & condensaton)HgI2, CdS, ZnS, NH4X Hg2C2, CdS*olecular 3rganicsBCan be used wth materas that decompose or have excessve vapor pressure at metng pont or wth destructve phase transtons or extremey hgh metng ponts or whch react wth contaners.Materas must have reasonabe vapor pressure at temperature where surface knetcs s adequate Typcay sowDmcut to controChemca vapor deposton(open ow)Refractores: SC, PBNSemconductor eptaxy!Chemca vapor transport(cosed system)TO2, EuS, "haogen amps" SnO2, In2S3Very sow; batch processSouton/FuxADP, KDP, RefractoresHydrotherma quartzDamond: 1450 C, 742 kps, N uxProtens, Mneras, Mo2CHgh Tc superconductors; BSrCaCuOMortons tabesatLarge szes possbePotentay ow cost, arge scaeReduced temperatureess contaner contamnatonCan be nexpensveVery sowTemperature contro very mportantKeh often very smadopng dmcutDgresson on Segregaton and PurcatonEectronc materas are ony nterestng when dopedCarrer type: "n"Dopant: "P""Res": "1-20 ohms"Typca NumbersOn prevous abe, p = 1-20 Ohm (presumaby 1-20 O-cm)As you know: o = 1/p = ne For scon at 10 O-cm wth n = 1700 cm2/V-sec nP = 3.7x1014/cm3 nS = 2.33 gm/cm3) x(6.02x1023 atoms/moe) (28.068 gm/moe) = 4.997x1022 atoms per moe nP / nS = 7x10-9 = 7 ppb!Background mpurty eve must be sma on ths scae!SegregatonCoemcent can be greater or ess than untyNutrent voume s nteCauses ma|or probems wth dopant unformtyCan be resoved by addng dopant to mets durng growthOny works for K>1!Orgn of Segregaton: Bnary Phase DagramW. G. Pfann, Zone MetngUsng Segregaton for Purcaton:"Norma Freezng"n.b.: exacty the same process s used to grow arge snge crystas "from the met"!W. G. Pfann, Zone MetngImpurty Dstrbuton after Norma FreezngW. G. Pfann, Zone MetngConcept of Zone RenngMoten zone of ength s passed through ngot of ength LAso the process used to make "oat zone scon" W. G. Pfann, Zone MetngImpurty Dstrbuton after Snge Pass of Zone(Less emcent than norma freezng)W. G. Pfann, Zone MetngImpurty Dstrbuton from Mut-pass Zone Renngn.b.: k = 0.9524, /L = 0.01W. G. Pfann, Zone MetngTake Away LessonsSegregaton of mpurtes/dopants s a fact that you must dea wth as an aspect of materas preparatonSegregaton can be used as part of an eegant purcaton processZone renng can be very ehectve for materas purcatonCurrent Purcaton of Scon(Wkpeda) Siemens process: hgh-purty scon rods are exposed to trchorosane at 1150 C. The trchorosane gas decomposes and deposts addtona scon onto the rods, enargng them: 2 HSC3 S + 2 HC + SC4 Scon produced from ths and smar processes s caed polycrystalline silicon. Poycrystane scon typcay has mpurty eves of ess than 10-9.Czochrask GrowthSynthesis may or may not be part o. growth !a"s may be pre-synthesi5ed or a pre- measured 6uantity "s may be bubbled through !ametal%i 9 synthesi5ed .rom %i and 9, (or ',) Typical si5es Si - 1,C D, ,EE /g chargeA !a"s -7C D>e ha+e grown .rom a , g melt o. isotopically pure 210:1