semiconducto nanostructures i - fisi.polimi.it · characterization of epitaxial...

Semiconductor Nanostructures ISemiconductor Nanostructures I

H. von KänelH. von KänelH. von KänelH. von KänelLaboratorium für FestkörperphysikLaboratorium für Festkörperphysik

ETHZETHZ

Moore‘s LawMoore‘s LawMoore s LawMoore s Law

Doubling of transistor density in less than every 2 yearsDoubling of transistor density in less than every 2 years

Semiconductor Nanostructures

International Roadmap for SemiconductorsInternational Roadmap for SemiconductorsInternational Roadmap for SemiconductorsInternational Roadmap for Semiconductors


Evolution of LED performanceEvolution of LED performanceEvolution of LED performanceEvolution of LED performance

Haitz law for red and blue LEDsHaitz law for red and blue LEDs


M.R. Krames et al., J. Display Technol. M.R. Krames et al., J. Display Technol. 33, 160 (2007), 160 (2007)

Quantum efficiencies of HBLEDsQuantum efficiencies of HBLEDsQuantum efficiencies of HBLEDsQuantum efficiencies of HBLEDs

J M Philli t l L & Ph t R i 1 N 4 2007J M Philli t l L & Ph t R i 1 N 4 2007


J.M. Phillips et al. Laser & Photon Review 1, No. 4, 2007J.M. Phillips et al. Laser & Photon Review 1, No. 4, 2007

Periodic table of elementsPeriodic table of elementsPeriodic table of elementsPeriodic table of elements


Di d t tDi d t tDiamond structureDiamond structure


ZiZi bl d t tbl d t tZincZinc--blende structureblende structure


Comparison of wurtzite and zincComparison of wurtzite and zinc--ppblende structuresblende structures


Tetrahedrally bonded semiconductorsTetrahedrally bonded semiconductors(diamond, zinc blende)(diamond, zinc blende)


Variation of bandgap with lattice Variation of bandgap with lattice parameterparameter

UVUV--green group III nitridesgreen group III nitridesYellowYellow--red zinc blende arsenides red zinc blende arsenides -- phosphidesphosphides


M.R. Krames et al., J. Display Technol. M.R. Krames et al., J. Display Technol. 33, 160 (2007), 160 (2007)

Consequences of strainConsequences of strainConsequences of strainConsequences of strain

Strain affects electronic structure, optical and Strain affects electronic structure, optical and t t tit t titransport propertiestransport properties

Strain affects crystal quality through defect Strain affects crystal quality through defect y q y gy q y gformationformation

Strain affects growth modesStrain affects growth modesStrain affects growth modesStrain affects growth modes

Strain affects the stability of phasesStrain affects the stability of phases


Epitaxial growth modesEpitaxial growth modesEpitaxial growth modesEpitaxial growth modes

FrankFrank--van van der Merweder Merwe

VolmerVolmer--WeberWeber StranskiStranski--KrastanowKrastanow


Structural data of group III nitridesStructural data of group III nitridesStructural data of group III nitridesStructural data of group III nitrides

Room temperature data forRoom temperature data for–– Lattice parametersLattice parameters–– Thermal expansionThermal expansion


Thermal expansionThermal expansion

AlAl22OO33(0001) substrates(0001) substratesAlAl22OO33(0001) substrates(0001) substrates

Notice rotation of overlayer by 30 degrees!Notice rotation of overlayer by 30 degrees!


Notice rotation of overlayer by 30 degrees!Notice rotation of overlayer by 30 degrees!Misfit for GaN f = Misfit for GaN f = --16.1 %16.1 %

Si(111) substratesSi(111) substratesSi(111) substratesSi(111) substrates

Misfit for GaN f = 16.9 %Misfit for GaN f = 16.9 %


Strain relieving mechanismsStrain relieving mechanismsStrain relieving mechanismsStrain relieving mechanisms

Plastic relaxation: Formation of misfit Plastic relaxation: Formation of misfit dislocationsdislocations

Elastic relaxation: Surface corrugation, island Elastic relaxation: Surface corrugation, island formationformationformationformation

Formation of epitaxially stabilized phasesFormation of epitaxially stabilized phases


Strain relaxation by dislocationsStrain relaxation by dislocationsStrain relaxation by dislocationsStrain relaxation by dislocations

a)a) Coherent interface, Coherent interface, compressively strained filmcompressively strained film

b)b) Incoherent interface, relaxed filmIncoherent interface, relaxed film


compressively strained filmcompressively strained film

Critical thickness for plastic relaxationCritical thickness for plastic relaxationCritical thickness for plastic relaxationCritical thickness for plastic relaxation

a)a) Pure edge dislocations with Burgers vector b = 2.2 ÅPure edge dislocations with Burgers vector b = 2.2 Å

6060°° di l ti ith b 3 8 Ådi l ti ith b 3 8 Å


b)b) 6060°° dislocations with b = 3.8 Ådislocations with b = 3.8 Å

Geometry of 60Geometry of 60--degree dislocationsdegree dislocationsGeometry of 60Geometry of 60 degree dislocationsdegree dislocations

(111)(111)

-b=a/2[011]

n

[110]

TD

� �

b=a/2[011]

p

(001)

MD

�

�m

p

[110]-

(001)

[110]

A.E. Blakeslee, MRS Symp. Proc. A.E. Blakeslee, MRS Symp. Proc. 148148, 217 (1989), 217 (1989)


Propagation of dislocation loops Propagation of dislocation loops p g pp g pin {111} planesin {111} planes


Dislocation control by patterningDislocation control by patterning

P. P. ZaumseilZaumseil et al. et al. J. Appl. J. Appl. PhysPhys 109 023511109 023511Phys.Phys. 109, 023511 109, 023511 (2011)(2011)

6060--degree dislocationsdegree dislocations

A.E. Blakeslee, MRS Symp. Proc. A.E. Blakeslee, MRS Symp. Proc. 148148, 217 (1989), 217 (1989)


Aspect ratio trapping (ART)Aspect ratio trapping (ART)Aspect ratio trapping (ART)Aspect ratio trapping (ART)


Lateral epitaxial overgrowth (LEO)Lateral epitaxial overgrowth (LEO)Lateral epitaxial overgrowth (LEO)Lateral epitaxial overgrowth (LEO)

Marachand et alMarachand et alMarachand et al.Marachand et al.

Appl. Phys. Lett. Appl. Phys. Lett. 7373, 747 (1998), 747 (1998)

1.1. Nucleation in mask openingsNucleation in mask openings2.2. Lateral overgrowthLateral overgrowth33 CoalescenceCoalescence


3.3. CoalescenceCoalescence

Elastic strain relaxation by island Elastic strain relaxation by island formationformation


Normalized free energy for island Normalized free energy for island gygyformationformation

F/FF/F aVaV3/23/2 b Vb VF/FF/Fc c = aV= aV3/2 3/2 –– b Vb V


STM monitoring of Ge island STM monitoring of Ge island ggformation on Si(001)formation on Si(001)

l t lli W tipolycrystalline W tip

Vbias

sample

piezotube

It

sample tube

feedback z

x,y drive


Shape evolution sequenceShape evolution sequenceShape evolution sequenceShape evolution sequenceShape evolution sequenceShape evolution sequenceShape evolution sequenceShape evolution sequenceA. Rastelli et al., Phys. Rev. Lett. A. Rastelli et al., Phys. Rev. Lett. 8787, 256101 (2001), 256101 (2001)

Prepyramid T-Pyramid Pyramid

Super DomeT-Dome Dome

Super-Dome


70×70×11 nm3

120×120×27 nm3

GaN quantum dots on AlNGaN quantum dots on AlNGaN quantum dots on AlNGaN quantum dots on AlNHRTEMHRTEM STEMSTEM

T. Xu et al., J. Appl. Phys. T. Xu et al., J. Appl. Phys. 102102, 073517 (2007), 073517 (2007)

K. Hoshino et al., phys. Stat. Sol. (b) K. Hoshino et al., phys. Stat. Sol. (b) 240240, 322 (2003), 322 (2003)

Compressive misfit Compressive misfit –– 2.5 %2.5 %Truncated pyramidal shapeTruncated pyramidal shapeW tti l i ibl i STEMW tti l i ibl i STEM


Wetting layer visible in STEMWetting layer visible in STEM

PbSe quantum dots on PbTe(111)PbSe quantum dots on PbTe(111)PbSe quantum dots on PbTe(111)PbSe quantum dots on PbTe(111)

G Springholz et al ScienceG Springholz et al Science 282282 734 (1998)734 (1998)


G. Springholz et al., Science G. Springholz et al., Science 282282, 734 (1998), 734 (1998)

fcc ordering of dot SLfcc ordering of dot SLgg

G. Springholz et al.G. Springholz et al.

Science Science 282282, 734 (1998), 734 (1998)


GaN columns on AlN/Si(111)GaN columns on AlN/Si(111)GaN columns on AlN/Si(111)GaN columns on AlN/Si(111)

Potential for columnar LEDs with much higher Potential for columnar LEDs with much higher li ht t ti ffi ili ht t ti ffi ilight extraction efficiencylight extraction efficiency


Epitaxial stabilization of phasesEpitaxial stabilization of phasesEpitaxial stabilization of phasesEpitaxial stabilization of phases


Cubic GaN/GaAs(001)Cubic GaN/GaAs(001)Cubic GaN/GaAs(001)Cubic GaN/GaAs(001)

A. Trampert and K. Ploog, A. Trampert and K. Ploog, C st Res TechnolC st Res Technol 3535Cryst. Res. Technol. Cryst. Res. Technol. 3535, , 793 (2000)793 (2000)

Misfit 20%!Misfit 20%!C i id l i 5C i id l i 5 44


Coincidence lattice 5 aCoincidence lattice 5 acc--GaN GaN = 4 a= 4 aGaAsGaAs

Mixing free energy of InMixing free energy of In GaGa N alloysN alloysMixing free energy of InMixing free energy of InxxGaGa11--xxN alloysN alloys

C itiComposition x

A. Tabata et al., Appl. Phys. Lett. A. Tabata et al., Appl. Phys. Lett. 8080, 769 (2002), 769 (2002)


Alloy stabilization by biaxial strainAlloy stabilization by biaxial strainy yy y

A. Tabata et al., Appl. Phys. A. Tabata et al., Appl. Phys. Lett. Lett. 8080, 769 (2002), 769 (2002)

a)a) Unstrained cUnstrained c--InGaN alloys on cInGaN alloys on c--GaN(001) bufferGaN(001) buffer)) yy ( )( )b)b) Complete suppression of spinodal decomposition for T = TComplete suppression of spinodal decomposition for T = Tss

Semiconductor NanostructuresSemiconductor Nanostructures

Thermal mismatch: Wafer bending and cracksThermal mismatch: Wafer bending and cracksgg

30 µm Ge/Si(001)30 µm Ge/Si(001)


Growth on patterned Si substratesGrowth on patterned Si substratesGrowth on patterned Si substratesGrowth on patterned Si substratesMicromachinedMicromachined Si pillarsSi pillars Ge coverage: 8 Ge coverage: 8 µµmm

C V Fal b et al ScienceC V Fal b et al Science 335335 1330 (2012)1330 (2012)


C.V. Falub et al., Science C.V. Falub et al., Science 335335, 1330 (2012), 1330 (2012)

SelfSelf--limiting lateral growthlimiting lateral growthg gg g



Elastic relaxation of thermal strainElastic relaxation of thermal strainElastic relaxation of thermal strainElastic relaxation of thermal strain



Characterization of epitaxial nanostructuresCharacterization of epitaxial nanostructuresCharacterization of epitaxial nanostructuresCharacterization of epitaxial nanostructures

Structural:Structural:–– Reflection high energy electron diffraction (RHEED)Reflection high energy electron diffraction (RHEED)–– Optical reflection spectroscopyOptical reflection spectroscopy–– XX--ray diffractionray diffraction–– Transmission electron microscopyTransmission electron microscopy

Secondary ion mass spectrometry (SIMS)Secondary ion mass spectrometry (SIMS)–– Secondary ion mass spectrometry (SIMS)Secondary ion mass spectrometry (SIMS)–– Rutherford backscattering spectrometry (RBS)Rutherford backscattering spectrometry (RBS)

Optical:Optical:Optical:Optical:–– Reflection & transmissionReflection & transmission–– PhotoluminescencePhotoluminescence–– Raman scatteringRaman scattering

Electrical:Electrical:–– Conductivity & Hall effectConductivity & Hall effect


Molecular beam epitaxyMolecular beam epitaxyMolecular beam epitaxyMolecular beam epitaxy


RHEED pattern from a rectangular RHEED pattern from a rectangular p gp g22--D latticeD lattice


Typical RHEED pattern (0Typical RHEED pattern (0thth Laue zone)Laue zone)Typical RHEED pattern (0Typical RHEED pattern (0thth Laue zone)Laue zone)


RHEED pattern of Si(111)RHEED pattern of Si(111)--77××77RHEED pattern of Si(111)RHEED pattern of Si(111) 77 77

Incident electron beam along <11Incident electron beam along <11--2> azimuth2> azimuth


Incident electron beam along <11Incident electron beam along <11 2> azimuth2> azimuth

Rough GaN layer on AlN bufferRough GaN layer on AlN bufferRough GaN layer on AlN bufferRough GaN layer on AlN buffer

Diffraction spots due to transmission through islandsDiffraction spots due to transmission through islands


RHEED oscillations (schematic)RHEED oscillations (schematic)RHEED oscillations (schematic)RHEED oscillations (schematic)


Coplanar highCoplanar high--angle xangle x--ray diffractionray diffractionCoplanar highCoplanar high--angle xangle x--ray diffractionray diffraction

HRXRD analysis: 30 HRXRD analysis: 30 µµm Ge towers vs. continuous film m Ge towers vs. continuous film HRXRD analysis: 30 HRXRD analysis: 30 µµm Ge towers vs. continuous film m Ge towers vs. continuous film

Semiconductor NanostructuresC.V. Falub et al., Science C.V. Falub et al., Science 335335, 1330 (2012), 1330 (2012)

HRXRD analysis of 30 HRXRD analysis of 30 µµm Ge towers m Ge towers HRXRD analysis of 30 HRXRD analysis of 30 µµm Ge towers m Ge towers

Semiconductor NanostructuresC.V. Falub et al., Science C.V. Falub et al., Science 335335, 1330 (2012), 1330 (2012)

Strain state of cStrain state of c--GaN/InGaN/GaN(001)GaN/InGaN/GaN(001)/ / ( )/ / ( )

(a) d(a) dInGaNInGaN = 30 nm= 30 nm

Tabata et alTabata et alTabata et al.Tabata et al.

Appl. Phys. Lett. Appl. Phys. Lett. 8080, 769, 769

(2002)(2002)

(b) d(b) dInGaNInGaN = 3 nm= 3 nm


Near band edge PL of alloysNear band edge PL of alloysea ba d edge o a oysea ba d edge o a oys

S. Chichibu, nature materials 5, 810 (2006)S. Chichibu, nature materials 5, 810 (2006)


Periodic table of elementsPeriodic table of elementsPeriodic table of elementsPeriodic table of elements


GaN PL intensity vs TDDGaN PL intensity vs TDDGaN PL intensity vs. TDDGaN PL intensity vs. TDD

Theory: J.H. You, J. Appl. Phys. Theory: J.H. You, J. Appl. Phys. 101101, 023516 (2007), 023516 (2007)


y , pp yy , pp y , ( ), ( )

AlAl GaGa N/GaN heterostructureN/GaN heterostructureAlAl0.090.09GaGa0.910.91N/GaN heterostructureN/GaN heterostructure

Sheet electron density 2.12 Sheet electron density 2.12 ×× 10101212 cmcm--2 2 at 4 Kat 4 KMobility 60‘000 cmMobility 60‘000 cm22/Vs at 4 K/Vs at 4 K

C.R. Elsass et al., Jap. J. Appl. Phys. 39, L1023 (2000) C.R. Elsass et al., Jap. J. Appl. Phys. 39, L1023 (2000)


Mobility limiting scattering mechanismsMobility limiting scattering mechanismsMobility limiting scattering mechanismsMobility limiting scattering mechanisms


D. Jena et al., Am. Phys. Soc. March Meeting, Seattle, Washington, 2001D. Jena et al., Am. Phys. Soc. March Meeting, Seattle, Washington, 2001

Elementary processes in epitaxyElementary processes in epitaxyElementary processes in epitaxyElementary processes in epitaxy


IIIIII V MBE at LV MBE at L NESS in ComoNESS in ComoIIIIII--V MBE at LV MBE at L--NESS in ComoNESS in Como


Generic CVD systemGeneric CVD systemGeneric CVD systemGeneric CVD system


Epitaxial SiGe growth by CVDEpitaxial SiGe growth by CVDEpitaxial SiGe growth by CVDEpitaxial SiGe growth by CVD


Temperature dependence of CVD Temperature dependence of CVD growth ratesgrowth rates


CVD growth rate for Si homoepitaxyCVD growth rate for Si homoepitaxyCVD growth rate for Si homoepitaxyCVD growth rate for Si homoepitaxy

E.C. Everstyn, Philips Research Rept. E.C. Everstyn, Philips Research Rept. 1919, 45 (1974), 45 (1974)


Group III nitride MOCVDGroup III nitride MOCVDpp

Aixtron planetary reactorAixtron planetary reactorAixtron planetary reactorAixtron planetary reactor

Note numerous gas phase reactionsNote numerous gas phase reactions

M. Dauelsberg, M. Dauelsberg, ICMOVPE XIII, May ICMOVPE XIII, May 2222--26 26 2006, 2006, Miyazaki, JapanMiyazaki, Japan


Deposition of SiGe by LEPECVDDeposition of SiGe by LEPECVD

200 mm LEPECVD200 mm LEPECVD200 mm LEPECVD200 mm LEPECVDsystemsystem

ArAr ArAr

SiSi++HH

HH ++

ArAr

ArArArArSiSi

HHHH

HHHH

ArArArArArAr

GeGeHHHH

HH++

HH ++

ArArGeGe

HHHH

HHHH

ArAr

SiSi GeGeGeGe SiSi SiSi SiSiGeGe

Principle of lowPrinciple of low--energy energy plasmaplasma--enhanced CVD:enhanced CVD:HighHigh--currentcurrent lowlow--voltage voltage arc dischargearc discharge HH++arc dischargearc dischargeSiHSiH44 and GeHand GeH44 are transformed are transformed into highly reactive radicalsinto highly reactive radicals

Very high growth rates (0 5Very high growth rates (0 5 µm/min)µm/min)Very high growth rates (0.5 Very high growth rates (0.5 µm/min) µm/min) possible at low substrate possible at low substrate temperaturestemperatures

Hydride vapor phaseHydride vapor phase epitaxyepitaxyHydride vapor phase Hydride vapor phase epitaxyepitaxy

Typical substrate temperatures 1000Typical substrate temperatures 1000--11001100ooCCGrowth rates of several 100 Growth rates of several 100 µm/hµm/h


semiconducto nanostructures i - fisi.polimi.it · characterization of epitaxial...

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