MOCVD

基本内容MOCVD和MBE—III-V半导体的主要外延手段半导体异质结基本结构：量子阱，线，点应变异质结：基本性质和外延尺寸纯度金属有机气相化学外延(MOCVD)------III-V半导体生产的主力PH3AsH3SiH4DEZnTMAlTMGaTMIn排气口GaCH3CH3CH3AsH3GaAs3CH4扩散吸附解吸附扩散反应分子束外延(MolecularBeamEpitaxy)------原子级的外延手段GaAs10-8Torr快门加热线圈GaInAlBeAsSiSb衬底加热器P基本参数：1.个源炉束流（温度）=组分和生长速率；2.衬底温度：生长速率和生长模式RHEED固体源高能电子枪荧光屏MOCVD和MBE的基本特征小结平衡化学反应生长，生长速度有浮动。材料生长依赖气相源的选择生长真空比较低，化学反应中有H+进入。生长速率比较高，适合大规模生产。不能原位监测生长情况。非平衡物理生长，生长精度高。生长特征依赖于源材料分子在衬底表面的吸附特性。可以任意选择组合源材料。生长真空高，材料纯度比较好。生长速率缓慢。原位监测生长情况和生长厚度III-V和IV半导体基本能带结构-------GaAs和GekEΓ6Γ8Γ71.不同能带的电子波函数在空间扩展和自旋不一样，决定跃迁定则以及偏振方向。2.能带的简并导致吸收系数增大。EgEg异质结量子结构------量子阱，线，点晶格动量/态密度1.限制载流子，提高复合效率。2.能级量子化，减少态密度，降低激光器阈值电流。3.修改能带的色散特征。应变异质结-------外延层与衬底的晶格常数差别压应变：aa0,InGaAs/GaAs,GaSb/GaAs无应变a=a0,AlGaAs/GaAs张应变aa0,GaAsP/GaAs,GaAsN/GaAs厚度增加，应变能增加，超过某一厚度hc，发生驰豫产生大量位错缺陷为什么会出现应变结构：III-V二元半导体(N除外)，晶格常数越大，带隙越小应变补偿结构kEΓ6Γ8Γ7EgInGaAs:压应变Γ8简并分离，减小吸收系数。应变对能带的影响：应变修改各个能带的位置ε=(a-a0)/a0εtLt+εcLc=01.每层厚度均小于临界厚度。2.异质结面易产生大量缺陷。3.垂直方向无应变。Ternaryalloy:Eg(AxB1-xC)=xEg(AC)+(1-x)Eg(BC)-bx(1-x)Quaternaryalloy:Eg(AxB1-xCyD1-y)={x(1-x)[yEg(ABC)+(1-y)Eg(ABD)]+y(1-y)[xEg(ACD)+(1-x)Eg(BCD)]}/[x(1-x)+y(1-y)]Eg(BxCyD1-x-yA)={xyEg(BCA)+x(1-x-y)Eg(BDA)+y(1-x-y)Eg(CDA)}/{xy+x(1-x-y)+y(1-x-y)}A(300)Eg(300K,)GaAs5.653251.424AlAs5.66113.03InAs6.05830.417GaP5.45052.886AlP5.46723.56InP5.86791.4236(AlxGa1-x)0.5In0.5PEg=1.91+0.61xAlGaInAs(lowAlandGa)Oh=TdCiTdC6vOC:cyclic(n)SO(3),SO(2)D:dihedral(n2(2))T:tetrahedral(23)O:octahedral(432)kEΓ6Γ8Γ7EgCrystalsutructureEnergystructureCompletecrystalEnergybandUncompletecrystallocalizedstate能级结构?为什么要学习群论以及表示理论AtomconfigurationMulti-atommulti-electronHamiltonian(firstprinciple)+dynamicsGrouptheory(symmetry)Meanfieldtheory:ElectronicstructureErVm222[Pa,H]=0,degeneracyofHcorrespondingtoIrreducibleRepresentationofG,l|Tj()|,i=cs(ij|l)*,Wigner-EckartTheorem,transitionelement:PCompleteorthonormalbasisSubductionSymmetry-adaptedbasis=ciiExpandingiH=iEETi,….k,P=Pi,Luttinger-Kohnparameter,形变势参数,piezoelectric,axialandvectorSplittingofenegylevel,G1G0,CrystalFieldtheory,G=G1G0群论基本概念(G,•):1.c=ab2.(ab)c=a(bc)3.ae=a4.aa-1=e?Group{e,C3,C32,v,v1,v2}SubgroupCoset(equivalentclass)Invariantgroup,QuotientgroupSemidirectproductConjugateclass{e,C3,C32},{e,v}Homomorphism:f(a)ºf(b)=f(a•b)D(g):aGP(a)Pa,PaLLnmjnkinjmRRiknkinjmnkkajmRRikARruRrueEARruRrVRruejiji,,,mnjinkkajmRRikRruRrVRrueji,mnjnkjimnmnjnkjinmRRikASEAHeji,,,,,RelationbetweenBlochTheoremandTightbindingnhhnRrikmkmkrikmkRruerrerh,slmYrnlRrnlmsu,YlmNormalizationSpericalCartisianY00sSqrt(1/4)11Y10pzSqrt(3/4)coszY11cpySqrt(3/4)sincosxY11spySqrt(3/4)sinsinyY20d0Sqrt(5/16)3cos2-12z2-x2-y2Y21cd1cSqrt(15/4)sincoscoszxY21sd1sSqrt(15/4)sincossinzyY22cd2cSqrt(15/16)sin2cos2x2-y2Y22sd2sSqrt(15/16)sin2sin22xyHssEssHssEsxlHspExxl2Hpp+(1-l2)HppExylmHpp-lmHppExzlnHpp-lnHppKoster-Slater1954himimhimhhRRikimimhimhhhhatomhimRRikimkimimknhhimRikkimhnlmsaaiihimRxuRxueEaRxRxVRxuerarRruerRruPaDgdRruhhhh,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,TightbindingLCAOVcrVSlVSlVcrCrystalFieldsplittingHAsHApHBsHBpHssHspH*spHppHppGe(Chadi)-15.74-7.33-15.74-7.33-1.702.302.304.07-1.05Ge(Harrison)-15.15-7.33-15.15-7.33-1.792.362.364.15-1.04GaAs(Chadi)-12.33-5.67-17.35-7.86-1.692.062.733.51-0.96GaAs(Harrison)-11.55-5.67-18.91-8.98-1.792.362.364.15-1.04RoadmarkoftightbindingHarrison.W.A,ElectronicstructureandpropertiesofSolid.Chadi.D.J,Phy.Rev.,1977,B16:3572Multibandk•Pmethodintint2020,5.0,intint,,,EEEjpkpkimjpkimEHijjirenkrikSameforeachmaterialCompletecrystalijnmnmnmEEEjppimmm,intint0,,05.0,intint,2LuttingerandKohnPhys.Rev.97.869(1955)2/3222TmkNBStraininepitaxialfilmc11c12c12c11c11c12c12c12c12c44c44c4400PiezoelectriceffectjkijkijsePCriticalthicknessMathews&Blakeslee