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Презентация на тему Identification of Defects and Secondary Phases in Reactively Sputtered Cu2 ZnSnS4 Thin Films

OutlineMotivationProblems with characterization of thin filmsExperimental approachResultsX-ray diffractionRaman SpectroscopyTransmission Electron MicroscopyScanning Auger MicroscopySummary & Acknowledgements
Identification of Defects and Secondary Phases in Reactively Sputtered Cu2ZnSnS4 Thin FilmsVardaan OutlineMotivationProblems with characterization of thin filmsExperimental approachResultsX-ray diffractionRaman SpectroscopyTransmission Electron MicroscopyScanning Auger MicroscopySummary & Acknowledgements Motivation – Phase EquilibriumCZTS is a line compound between Cu2SnS3 and ZnSTheoretically Motivation – Crystal StructureCrystal structures of secondary phases similar to CZTSAll primary Experimental ApproachSubstrateCuZnSnIntroduce H2S into chamber during sputter depositionSulfur is incorporated into the Characterization - XRDVarying Zn/(Cu+Sn) RatioZn/(Cu+Sn) ratio is varied while holding Cu/Sn ratio Characterization - XRDVarying Cu/(Zn+Sn) RatioCu/(Zn+Sn) ratio is varied while holding Zn/Sn ratio Characterization – RamanVarying Zn/(Cu+Sn) RatioRaman spectra show only minor changes even though Device FabricationGlass Substrate3000 µmMolybdenum Layer1 µm1.75 µmCdS (n-type)55 nmZnO:Al (n-type)340 nmAluminum GridCZTS Device CharacterizationI-V MeasurementEQE MeasurementFirst CZTS devices grown by a reactive sputtering processEfficiency Characterization - TEM500nmDetrimental secondary phase interspersed in CZTS matrixStacking faults in the Characterization - AugerRaster beam over sputtered surface of sample and scan for Characterization - CdZnSCd penetration into ZnS lowers the cubic-hexagonal transition temperatureStacking faults Characterization - AugerSnCdOverlay Sn and Cd signalCd ion exchanges with Zn during SummaryCZTS thin films were grown using Reactive SputteringFilms were characterized using X-ray AcknowledgementsUS Department of Energy, Office of Basic Energy Sciences as part of QuestionsQuestions?
Слайды презентации

Слайд 2 Outline





Motivation
Problems with characterization of thin films
Experimental approach
Results
X-ray diffraction
Raman

OutlineMotivationProblems with characterization of thin filmsExperimental approachResultsX-ray diffractionRaman SpectroscopyTransmission Electron MicroscopyScanning Auger MicroscopySummary & Acknowledgements

Spectroscopy
Transmission Electron Microscopy
Scanning Auger Microscopy
Summary & Acknowledgements


Слайд 3 Motivation – Phase Equilibrium





CZTS is a line compound

Motivation – Phase EquilibriumCZTS is a line compound between Cu2SnS3 and

between Cu2SnS3 and ZnS
Theoretically even a 2-3% compositional variation

could lead to phase separation

Ternary Phase Diagram

Binary Phase Diagram

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.


CZTS


Слайд 4 Motivation – Crystal Structure





Crystal structures of secondary phases

Motivation – Crystal StructureCrystal structures of secondary phases similar to CZTSAll

similar to CZTS
All primary peaks overlap and hard to

separate
Low intensity peaks cannot be seen easily in thin films

Theoretical XRD Patterns of CZTS, Cu2SnS3, and ZnS


Слайд 5 Experimental Approach








Substrate
Cu
Zn
Sn
Introduce H2S into chamber during sputter deposition
Sulfur

Experimental ApproachSubstrateCuZnSnIntroduce H2S into chamber during sputter depositionSulfur is incorporated into

is incorporated into the film in one step (no

anneal)
Expect to see higher densities and improved film quality

Reactive Sputtering


Слайд 6 Characterization - XRD





Varying Zn/(Cu+Sn) Ratio
Zn/(Cu+Sn) ratio is varied

Characterization - XRDVarying Zn/(Cu+Sn) RatioZn/(Cu+Sn) ratio is varied while holding Cu/Sn

while holding Cu/Sn ratio constant
Impossible to determine difference between

CZTS, CTS, and ZnS from XRD pattern

(101)

(200)

(220)

(312)

(112)

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.







Слайд 7 Characterization - XRD





Varying Cu/(Zn+Sn) Ratio
Cu/(Zn+Sn) ratio is varied

Characterization - XRDVarying Cu/(Zn+Sn) RatioCu/(Zn+Sn) ratio is varied while holding Zn/Sn

while holding Zn/Sn ratio constant
Need to get very far

off 2:1:1 stoichiometry before any CuxS phases can be seen
CuxS can be removed with KCN etch

(101)

(200)

(220)

(312)

(112)

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.






Слайд 8 Characterization – Raman





Varying Zn/(Cu+Sn) Ratio
Raman spectra show only

Characterization – RamanVarying Zn/(Cu+Sn) RatioRaman spectra show only minor changes even

minor changes even though composition is varied dramatically
No evidence

of the CuxS phase shown by other groups at growth temperatures higher than 500C

Varying Cu/(Zn+Sn) Ratio


Слайд 9 Device Fabrication





Glass Substrate
3000 µm
Molybdenum Layer
1 µm
1.75 µm
CdS (n-type)
55

Device FabricationGlass Substrate3000 µmMolybdenum Layer1 µm1.75 µmCdS (n-type)55 nmZnO:Al (n-type)340 nmAluminum

nm
ZnO:Al (n-type)
340 nm
Aluminum Grid
CZTS Absorber (p-type)
CZTS Device Stack
Zn-rich films

incorporated into standard CIGS device stack for testing

ZnO

85 nm

ZnO

ZnO:Al

CdS

CZTS

Mo

SEM Image


Слайд 10 Device Characterization





I-V Measurement
EQE Measurement
First CZTS devices grown by

Device CharacterizationI-V MeasurementEQE MeasurementFirst CZTS devices grown by a reactive sputtering

a reactive sputtering process
Efficiency = 1.35%
Degraded EQE clearly points

to undetected defects in the absorber

Слайд 11 Characterization - TEM





500nm


Detrimental secondary phase interspersed in CZTS

Characterization - TEM500nmDetrimental secondary phase interspersed in CZTS matrixStacking faults in

matrix

Stacking faults in the secondary phase point to a

transition between cubic and hexagonal crystal structures



Слайд 12 Characterization - Auger





Raster beam over sputtered surface of

Characterization - AugerRaster beam over sputtered surface of sample and scan

sample and scan for Cu, Zn, Sn
Overlay Cu, Zn,

Sn signal
Composition variation points to CZTS / ZnS (Zn-rich)

2 um

Cu

Zn

Sn

CZTS

ZnS


Слайд 13 Characterization - CdZnS





Cd penetration into ZnS lowers the

Characterization - CdZnSCd penetration into ZnS lowers the cubic-hexagonal transition temperatureStacking

cubic-hexagonal transition temperature
Stacking faults in TEM images are created

during CBD of CdS layer

CdS – ZnS Phase Diagram

(101)

H-ZnS

(220)

(312)

(112)


XRD before and after CBD

C

C + H

H

Chen et al.“Solid State Phase Equilibria in the ZnS-CdS System." Materials Research Bulletin. 23. (1988): 1667-1673. Print.


Слайд 14 Characterization - Auger





Sn
Cd
Overlay Sn and Cd signal
Cd ion

Characterization - AugerSnCdOverlay Sn and Cd signalCd ion exchanges with Zn

exchanges with Zn during bath deposition and penetrates the

ZnS phase

CZTS

CdZnS

2 um


Слайд 15 Summary





CZTS thin films were grown using Reactive Sputtering
Films

SummaryCZTS thin films were grown using Reactive SputteringFilms were characterized using

were characterized using X-ray Diffraction and Raman Spectroscopy
Full devices

have been grown and tested but are limited due to secondary phases in the films
Transmission Electron Microscopy and Scanning Auger Microscopy can be used to identify these secondary phases

Слайд 16 Acknowledgements





US Department of Energy, Office of Basic Energy

AcknowledgementsUS Department of Energy, Office of Basic Energy Sciences as part

Sciences as part of an Energy Frontier Research Center
http://www.er.doe.gov/bes/EFRC/index.html

Applied

Quantum Technologies
Local thin film solar startup
http://www.aqtsolar.com

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