Why are semiconductors useful to us(Why isn’t Si enough)

1、AnnouncementsHandouts - General Information; Syllabus; Lecture 1 NotesWhy are semiconductors useful to us? (Why isnt Si enough?)Review of the properties of siliconQuantifying the importance of silicon to the electronics industryRepresentative applications silicon is not suitable for (.at least not y

2、et)Which materials are semiconductors? (What are our choices?)Elemental semiconductorsCompound semiconductors - binaries1. III-Vs; 2. II-IVs; 3. IV-VIs; 4. I-VIIsAlloy semiconductors1. Ternaries; 2. Quarternaries; 3. Others: a) More than 4; b) Si-GeProperties vs. composition (Making sense of all the

3、 options)Crystal structureEnergy band structureCarrier type and transportOptical propertiesOther6.772/SMA5111 - Compound SemiconductorsLecture 1 - The Compound Semiconductor Palette - OutlineC. G. Fonstad, 2/03 Lecture 1 - Slide 1Physical, structuralCrystal structurediamondLattice period () 5.431Ene

4、rgy levelsEnergy gap (eV) 1.1Band symmetryindirect gapDensity of states (cm-3) Nc = 2.8 x 1019 Nv = 1.02 x 1019Electrical, charge carriers Electrons HolesLow field mobility (cm2/V-s) 1450 450Critical E-field (V/cm) 104 5 x 104Saturation velocity (cm/s) 107 107Effective mass (relative) ml 0.98 mlh 0.

5、16 mt 0.19 mhh 0.5OpticalAbsorption edge (gap) 1.1 mRadiative lifetime (s) few msTypical radiative Efficiency (%) 1%Important properties of siliconC. G. Fonstad, 2/03 Lecture 1 - Slide 2Light emittersLight emitting diodes, Laser diodesany wavelengthMid- and far-infrared detectors ( 1.1 m) Fiber comm

6、unication wavelengths = 1.3 and 1.55 mAtmospheric windows = 3 to 5 m and 8 to 12 mInfrared imaging arrays night visionThermophotovoltaic cells responding to 500 K black bodiesUltraviolet detectors ( 0.5 m)Solar blind detectors no response in visibleOptical modulatorsAmplitude modulation of light for

7、 fiber telecommVery-high speed electronicsSystems operating at 40 GHz and above for fiber telecommHigh temperature electronicsOperable at temperatures above 200C process monitoringCryogenic electronicsOperating at 4.2 K and below space instrumentationThings that cannot yet be made from siliconC. G.

8、Fonstad, 2/03 Lecture 1 - Slide 3Elemental semiconductorsColumn IV: C (diamond), Si, Ge, Sn (grey)All have the diamond structure:All are indirect band gapMaterials other than Si that are semiconductors:C. G. Fonstad, 2/03 Lecture 1 - Slide 4(Image deleted) See Fig 3a in: Sze, S.M. Semiconductor Devi

9、ces, Physics and TechnologyNew York, Wiley, 1985.(Image deleted) See Fig 1-5-6 in: Shur, M.S. Physics of Semiconductor DevicesEnglewood Clifs, N.J., Prentice-Hall,1990.Notice the trend (Eg): Sn: 0.08 eV Ge: 0.67 eV Si: 1.12 eV C: 5.5 eVDiamond and Ge are useful, but we will say little about them.Bin

10、ary compoundsThe choices are many-Column III with column V (the three-fives, III-Vs) : AIIIBVColumn II with column VI (the two-sixes, II-VIs): AIIBVIColumn IV with Column VI (the four-sixes, IV-VIs): AIVBVIColumn I with Column VII: AIBVII (these are insulators)To help us make sense of all these opti

11、ons we will find that there are clear trends (a method to the madness)The best way to start is by looking at plots of lattice period vs. energy gap.Materials other than Si that are semiconductors:C. G. Fonstad, 2/03 Lecture 1 - Slide 5Zinc blende lattice(GaAs shown)C. G. Fonstad, 2/03 Lecture 1 - Sl

12、ide 6Compound Semiconductors: The zinc blende lattice (Image deleted)See Fig 3a in: Sze, S.M. Semiconductor Devices, Physics and TechnologyNew York, Wiley,1985. (Image deleted) See Fig 3b in: Sze, S.M. Semiconductor Devices, Physics and TechnologyNew York, Wiley,1985.Diamond lattice(Image deleted)Se

13、e Fig 1-5-6 in: Shur, M.S. Physics of Semiconductor Devices Englewood Cliffs, N.J., Prentice-Hall, 1990.C. G. Fonstad, 2/03 Lecture 1 - Slide 7Compound Semiconductors: Direct vs indirect bandgapsBinary Compound Semiconductors: Zinc-blende III-Vs II-VIsC. G. Fonstad, 2/03 Lecture 1 - Slide 8Binary Co

14、mpound Semiconductors: Zinc-blende III-Vs II-VIsMaterial Semiconductor Crystal Lattice Energy BandSystem Name Symbol Structure Period(A) Gap(eV) TypeIII-V Aluminum phosphide AlP Z 5.4510 2.43 iAluminum arsenide AlAs Z 5.6605 2.17 iAluminum antimonide AlSb Z 6.1355 1.58 iGallium phosphide GaP Z 5.451

15、2 2.26 iGallium arsenide GaAs Z 5.6533 1.42 dGallium antimonide GaSb Z 6.0959 0.72 dIndium phosphide InP Z 5.8686 1.35 dIndium arsenide InAs Z 6.0584 0.36 dIndium antimonide InSb Z 6.4794 0.17 dII-VI Zinc sulfide ZnS Z 5.420 3.68 dZinc selenide ZnSe Z 5.668 2.71 dZinc telluride ZnTe Z 6.103 2.26 dCa

16、dmium sulfide CdS Z 5.8320 2.42 dCadmium selenide CdSe Z 6.050 1.70 dCadmium telluride CdTe Z 6.482 1.56 dKey: Z = zinc blende; i = indirect gap, d = direct gapC. G. Fonstad, 2/03 Lecture 1 - Slide 9Additional Semiconductors: Wurzite III-Vs and II-VIs Lead Salts (IV-VIs), Column IVMaterial Semicondu

17、ctor Crystal Lattice Energy BandSystemName Symbol Structure Period(A) Gap(eV) TypeIII-V Aluminum Nitride AlN W a = , c = 6.2 i(nitrides) Gallium Nitride GaN W a = 3.189, c = 5.185 3.36 dIndium Nitride InN W a = , c = 0.7 dII-VI Zinc Sulfide ZnS W a = 3.82, c = 6.28 3.68 d(wurtzite) Cadmium Sulfide C

18、dSW a = 4.16, c = 6.756 2.42 dIV-VI Lead Sulfide PbSR 5.9362 0.41 dLead Selenide PbSe R 6.128 0.27 dLead Telluride PbTe R 6.4620 0.31 dIV Diamond CD 3.56683 5.47 iSilicon SiD 5.43095 1.124 iGermanium GeD 5.64613 0.66 iGrey Tin SnD 6.48920 0.08 dIV-IV Silicon Carbide SiC W a = 3.086, c = 15.117 2.996

19、 i Silicon-Germanium SixGe1-x Z vary with x (i.e. an alloy) iKey: Z = zinc blende, W = wurtzite, R = rock salt; i = indirect gap, d = direct gapC. G. Fonstad, 2/03 Lecture 1 - Slide 10Binary Compound Semiconductors: mobility trendsC. G. Fonstad, 2/03 Lecture 1 - Slide 11 (Image deleted) See Fig 2 in

20、: Sze, S.M. ed., High Speed Semiconductor DevicesNew York, Wiley,1990. (Image deleted)See Fig 1 in: Sze, S.M. ed., High Speed Semiconductor DevicesNew York, Wiley,1990. Materials other than Si that are semiconductors: Binary compoundsMost have direct bandgaps. (very important to optoelectronic devic

21、e uses)They cover a wide range of bandgaps, but only at discrete points.They follow definite trendsThey can be grown in bulk form and cut into wafers.We still need more.Ternary alloysNot compounds themselves, but alloys of two binary compounds with one common element. (ternary compounds are of limit

22、ed interest)Ternary alloys have two elements from one column, one from another and there are two options: (III-V examples) AIII(1-x)BIII(x)CV = AIIICV(1-x)+ BIIICV(x) AIIIBV(1-y)CV(y) = AIIIBV(1-y)+ AIIICV(y)With ternary alloys we have access to a continuous range of bandgapsC. G. Fonstad, 2/03 Lect

23、ure 1 - Slide 12Ternary Alloy Semiconductors: 3 III-V examples, AlGaAs, InGaAs, InAlAsC. G. Fonstad, 2/03 Lecture 1 - Slide 13Ternary trends: Lattice period: linear with composition (Vegards Law) Band gaps: quadratic with composition; slope and curvature vary with band minimaC. G. Fonstad, 2/03 Lect

24、ure 1 - Slide 14Ternary trends: Most properties, such as effective mass, vary quadraticly and monotonically with alloy fraction. Alloy scattering is largest near a 50%mix and transport properties tend to notvary monotonically. C. G. Fonstad, 2/03 Lecture 1 - Slide 15Materials other than Si that are

25、semiconductors: Ternary alloysGive us access to continuous ranges of bandgaps, but as Eg varies so in general does a.Substrates are always binary and only come at discrete as.Thus to grow heterostructures we need different Eg layers, all with the same a, and ternaries dont do the full job. (Note: Al

26、GaAs is an important exception; since it is intrinsically lattice-matched to GaAs it was used in the first heterostructure work. However, soon more was needed.) Quarternary alloysQuarternaries mix 4 elements - there are 2 types: (III-V examples)1. 2 elements from one column, 2 from the other: (mixes

27、 of 4 binaries) AIII(1-x)BIII(x)CV(1-y)DV(y) = AIIICV(1-x)(1-y)+AIIIDV(1-x)y +BIIICVx(1-y)+BIIIDVxy2. 3 elements from one column, 1 from the other: (3 binary mixes) AIII(1-x-y)BIII(x)CIII(y)DV = AIIIDV(1-x-y)+BIIIDV(x)+CIIIDV(y) AIIIBV(1-x-y)CV(x)DV(y) = AIIIBV(1-x-y)+AIIICV(x)+AIIIDV(y)With quarter

28、nary alloys we have access to ranges of in materials that are all lattice-matched to a binary substrateC. G. Fonstad, 2/03 Lecture 1 - Slide 16III-V quarternaries: InGaAlAsC. G. Fonstad, 2/03 Lecture 1 - Slide 17III-V quarternaries: more examples InGaAsP and AlGaAsSbC. G. Fonstad, 2/03 Lecture 1 - S

29、lide 18III-V quarternaries: more examples GaInAsSbC. G. Fonstad, 2/03 Lecture 1 - Slide 19III-V quarternaries: more examples GaAlAsP and GaAlInPC. G. Fonstad, 2/03 Lecture 1 - Slide 20The III-V wurtzite quarternary: GaInAlNC. G. Fonstad, 2/03 Lecture 1 - Slide 21(Image deleted)See Fig 2a: Sze, S.M.

30、Physics ofSemiconductor Devices, 2nd ed.New York: Wiley, 1981Sowhere are we? Are all these semiconductors important? All have uses, but some are more widely used than others GaAs-based heterostructures InP-based heterostructures Misc. II-IVs, III-Vs, and others Important Binaries GaAs substrates, ME

31、SFETs InP substrates GaP red, green LEDs Important Ternaries and Quaternaries AlGaAs on GaAs HBTs, FETs, optoelectronic (OE) devices GaAsP on GaAs red, amber LEDs HgCdTe on CdTe IR imagers InGaAsP, InGaAlAs on InP OEs for fiber telecomm. InGaAlAs on InP ditto InGaAs on GaAs, InP ohmic contacts, quantum wells InGaAsP on GaAs red and IR lasers, detectors GaInAlN on various substrts. green, blue, UV LEDs, lasersC. G. Fonstad, 2/03 Lecture 1 - Slide 226.772/SMA5111 - Compound SemiconductorsLecture 1 - The Compound Semiconductor Pa