Deposition and CharacterisationDeposition and Characterisationofof Chalcogenide Chalcogenide Materials Materials

with the J/Lab FELwith the J/Lab FEL

Universityof SouthamptonUniversityof Southampton

Harvey N. Harvey N. RuttRutt Optoelectronics Research Centre

OverviewOverview

•• Two-week campaign November 2001. Two-week campaign November 2001.

•• PLD of PLD of ZnSe ZnSe thin films.thin films.

•• NIR absorption of NIR absorption of GaGa:La:S glasses.:La:S glasses.

Pulsed Laser Deposition of ZincPulsed Laser Deposition of ZincChalcogenideChalcogenide Optical Thin Films Optical Thin Films using using

JL-FEL.JL-FEL.

R. Peaty, H.N.R. Peaty, H.N. Rutt RuttOptoelectronics Research Centre

M. Shinn, J.F.M. Shinn, J.F. Gubeli Gubeli III, K. Jordan, G. Neil III, K. Jordan, G. NeilJefferson National Laboratories

Universityof Southampton

Aim Aim

•• Deposition ofDeposition of epitaxial epitaxial thin films. thin films.

•• Low optical loss.Low optical loss.

•• Room temperature IR Laser.Room temperature IR Laser.

•• High refractive index forHigh refractive index for waveguiding waveguiding..

Materials Materials

•• ZnSZnS and and ZnSe ZnSe host materials. host materials.•• Low Phonon energy.Low Phonon energy.•• CrCr2+2+ dopant shown to dopant shown to lase lase at 2.35µm. at 2.35µm.•• Sapphire and SrFSapphire and SrF22 substrate layers. substrate layers.•• Close lattice match with substrate.Close lattice match with substrate.•• Good thermal conductivity.Good thermal conductivity.•• Refractive Indices allowRefractive Indices allow waveguiding waveguiding..

Why PLD?Why PLD?

• Retains target stoichiometry.• High plume energy means lower

substrate temperatures required.• High deposition rate, easily adjustable

using pulse rate.• Deposition controlled by laser - no

shutters needed to stop film growth.

Laser Parameter ComparisonLaser Parameter Comparison

KrFKrF Excimer Excimer

• ��= 248nm.

• 1-50 Hz.• Pulse Energy = 0.4J.• Average power ~ 4W

• 40 ns pulses.

Free Electron LaserFree Electron Laser

• � = 1050nm, frequency doubled to 525nm.• 18 MHz.• µ-pulse energy ~0.25µJ• Laser power 5-10W (green)• 0.5 -1.7 ps pulses.

Why go to J-Labs?Why go to J-Labs?

• The ps/ns particulate debate.

• High average powers available.

• Excellent beam quality.

FEL Experimental ParametersFEL Experimental Parameters

• � = 525nm

• 50% doubling efficiency.

• Frequency = 18MHz

• Incident Power = 4.3W

[1] - Handbook of Optical Constants of Solids II, E.D. Palik

0.228459.2

0.796500.0

1.233619.9

Absorption depth(µm)

Wavelength(nm)

CubicCubic ZnSe ZnSe [1][1]

Vacuum ChamberVacuum ChamberTypical pressure reached = 1x10Typical pressure reached = 1x10-6-6 Torr Torr..Target to substrate distance = 55mm.Target to substrate distance = 55mm.

Vacuum Pump PipeVacuum Pump PipeDiameter = 100mmDiameter = 100mm

Silica LaserSilica LaserEntry WindowEntry Window

NN22 Venting Gas Venting Gas

Heater & ThermocoupleHeater & ThermocoupleElectrical ConnectionsElectrical Connections

Target MotorTarget MotorElectrical ConnectionsElectrical Connections

Removable SubstrateRemovable SubstrateHolder AssemblyHolder Assembly

Compressed AirCompressed AirCooling GasCooling Gas

RotatingRotating ZnSe ZnSe Target Target

Vacuum chamber under testVacuum chamber under test

Optical Beam PathOptical Beam Path

Focal length of finalFocal length of finalSilica lens = 49cmSilica lens = 49cm

LBO doubler crystal.LBO doubler crystal.

Focal lens scanningFocal lens scanningmotor.motor.

Moving platformMoving platformwhich scans laserwhich scans laserpoint across target.point across target.

Vacuum chamber.Vacuum chamber.

Laser Focus AlignmentLaser Focus Alignment

•• Initial Deposition on large area glass substrates.Initial Deposition on large area glass substrates.•• Check parallel alignment of target and substrateCheck parallel alignment of target and substrate

mount.mount.•• Focus laser onto target surface.Focus laser onto target surface.•• Ensure laser does not scan over target edges -Ensure laser does not scan over target edges -

film contamination from target holder.film contamination from target holder.•• Positioning of central deposition areaPositioning of central deposition area

(‘bull’s eye’) over substrate centre.(‘bull’s eye’) over substrate centre.•• Check PLA occurCheck PLA occurringring, not thermal evaporation., not thermal evaporation.

Alignment Deposition FringesAlignment Deposition Fringes

Ablation Target PatternsAblation Target Patterns

•• Thermal EvaporationThermal Evaporationgroove - rough surface.groove - rough surface.

•• Typical Ablation pattern -Typical Ablation pattern -smooth glassy surface.smooth glassy surface.

Right:Right: KrF KrFZnSeZnSe target, target,showing typicalshowing typicalablation pattern.ablation pattern.

Left:Left: FEL FELZnSeZnSe target. target.

Glass Substrate, Post DepositionGlass Substrate, Post Deposition

Hiccups from a rushedHiccups from a rushedtransatlantic flight!transatlantic flight!

• Susceptibility of substrate heater element tofailure..

• Lack of time to degas replacement heater(with brazed element).

• Running at 525nm, not 263nm - comparisonfilms deposited using KrF laser (247nm).

• Need to recaesiate FEL during the experiment..

But, even so…4 Interesting FilmsBut, even so…4 Interesting Films1 Substrate temperature 518ºC.

Deposition over 1 minute. Thickness = 240nm.2 Substrate temperature 395ºC.

Deposition over 1 minute. Thickness = 248nm.Heater broke.

3 Substrate temperature 503ºC.Deposition over 1 minute. Thickness = 334nm.

4 Substrate temperature 565ºC.Deposition over 1 minute. Thickness = 213nm.Brazed heater degassing - probable contamination.

DepositedDeposited ZnSe ZnSe Film FilmAluminium Substrate

mount shield withvisible fringes

Film #1 -fringes visible

0

2 0 0

4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

1 4 0 0

1 6 0 0

1 8 0 0

2 0 3 0 4 0 5 0 6 0

2 th e ta ( d e g r e e )

Cou

nts

(a.u

.)XRD Analysis of FEL FilmsXRD Analysis of FEL Films

FWHM = 0.3518º

Film 1 - Substrate Temperature 518ºC

Peak at 44.6º

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

2 0 3 0 4 0 5 0 6 0

2 th e ta ( d e g re e )

Cou

nts

(a.u

.)XRD Analysis of FEL FilmsXRD Analysis of FEL Films

FWHM = 0.3425º

Film 4 - Substrate Temperature 565ºC

Peak at 44.58º

Polycrystallinityand film defects -possibly causedby contamination

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

2 0 3 0 4 0 5 0 6 0

2 th e ta ( d e g re e )

Cou

nts

(a.u

.)XRD Analysis ofXRD Analysis of KrF KrF Films Films

FWHM = 0.0708º

Cr:ZnSe film - Substrate Temperature 550ºC

Peak at 43.62º

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

2 0 3 0 4 0 5 0 6 0

2 th e ta ( d e g re e )

Cou

nts

(a.u

.)XRD Analysis ofXRD Analysis of KrF KrF Films Films

FWHM = 0.2218º

ZnSe film - Substrate Temperature 575ºC

Peak at 43.7º

0102030405060708090

100

200 1200 2200 3200

W a ve le ngth ( nm )

Tran

smis

sion

(%)

01020304050607080

FEL Film 3 (503ºC)Bulk ZnSe

UV/visible SpecUV/visible Specttroscopyroscopy Analysis Analysis Comparison of Film 3 with ZnSe optical window

Transmission edgeintercept at 440nm forfilm. 450nm for ZnSe.

• Deposition rate for FEL greater by a factor of 5, compared to KrF.• XRD peak for SrF2 substrate close to ZnSe peak (SrF2 = 41.96º).

FEL andFEL and KrF KrF film Comparison film Comparison

–––0.222º43.7º574KrF0.130.9242458~3º~ 43.6º550KrF

0.191.3564460––402KrF0.161.1681459––499KrF

0.710.2134460.343º44.58º565FEL ��1.120.334451~2º~ 44.8º503FEL ��0.390.243445~2º44.56º395FEL ��0.800.2404490.352º44.6º518FEL ��

DepositionRate

(nm/s/W)

Thickness(nm)

TransmissionEdge (nm)FWHMXRD

PeakTemperature

(ºC)Film Type

ConclusionsConclusions

•• Too few results to reach any definiteToo few results to reach any definiteconclusions.conclusions.

•• TheThe ps ps/ns debate remains to be resolved./ns debate remains to be resolved.•• Preliminary results indicative ofPreliminary results indicative of epitaxial epitaxial films. films.•• UV/visible spectroscopy look good but thereUV/visible spectroscopy look good but there

are some questions.are some questions.•• Plenty of scope for more collaboration andPlenty of scope for more collaboration and

return visits to J-Labs.return visits to J-Labs.

Calorimetric Measurements of Near-IRCalorimetric Measurements of Near-IROptical Absorption Optical Absorption of of GaGa:La:S Glasses:La:S Glasses

using JL-FEL.using JL-FEL.

M. M. PetrovichPetrovich, H.N. , H.N. RuttRuttOptoelectronics Research Centre

M. Shinn, J.F. M. Shinn, J.F. Gubeli Gubeli III, K. Jordan, G. NeilIII, K. Jordan, G. NeilJefferson National Laboratories

Universityof Southampton

Outline Outline

•• GaGa:La:S glass technology.:La:S glass technology.•• Achievements and current efforts.Achievements and current efforts.•• GaGa:La:S transparency limit.:La:S transparency limit.•• Laser calorimetry.Laser calorimetry.•• Results, conclusions & further work.Results, conclusions & further work.

Why not silica glass?Why not silica glass?

AdvantagesAdvantages

• Stability & Inertness.• Low attenuation.• CDV fabrication.• EDFA devices.• Mature Technology.

LimitationsLimitations

• Opaque above 2�m.

• Limited rare earthsolubility.

• High Phonon Energy.• Small nonlinearity.

Fibre Amplifiers for Optical Fibre Amplifiers for Optical TelecomsTelecoms

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700

Atte

nuat

ion

[dB

/km

]

traditionalzero OH

Pr

Nd

Tm-Ho Tm-TbEr (C-ZBLAN)

Er (C-Si) Er (L)

Er (Te)

50 THz1310 nm

band S - bandC

band L - band

Wavelength [nm]

EDFA

GaGa:La:S:La:S glasses for photonic applications glasses for photonic applications

•• Visible to Mid-InfraredVisible to Mid-InfraredTransmission.Transmission.

•• High Rare Earth solubility.High Rare Earth solubility.•• Low Phonon Energy.Low Phonon Energy.•• High Nonlinearity.High Nonlinearity.•• FiberisableFiberisable..•• Good durability.Good durability.•• Non toxic.Non toxic.•• Highly Highly photorefractivephotorefractive..

Ga:La:S vs. Silica GlassSilicaSilicaGaGa:La:S:La:S

1.60.6Thermal Conductivity (W/m/K)

880540Specific Heat (J/kg/K)

>2200840Melting Temperature (ºC)

1175560Glass Transition Temperature (ºC)

0.5510.6Thermal Expansion Coefficient (10-6 K)

1150425Phonon Energy (cm-1)

1.210dn/dT (10-5 K)

0.2520Nonlinear Refractive index n2 (10-19 m2/W)

1.442.4Refractive Index n (@1.5 �m)

0.16 - 20.55 - 5Transparency window (�m)

Low Phonon Glass HostLow Phonon Glass Host

Pumppower

Non-radiative Decay

1.3 �mEmission

High Phonon E nergyHigh Phonon E nergy L ow Phonon E nergyL ow Phonon E nergy

Fluoride/Oxide Glass Sulphide/Chalcogenide Glass

Pumppower

PrPr3+3+ PrPr3+3+1.3 �mEmission

3.4 �mEmission

4.7 �mEmission

GaGa:La:S Fabrication Technology:La:S Fabrication Technology

•• Raw material Synthesis/Raw material Synthesis/

Purification.Purification.

•• Glass melting.Glass melting.

•• Polishing of Rods and Disks.Polishing of Rods and Disks.

•• PreformPreform manufacture by Extrusion manufacture by Extrusionor by the Rod-in-Tube method.or by the Rod-in-Tube method.

•• Etching.Etching.

•• Fibre drawing.Fibre drawing.

•• CharacterisationCharacterisation..

GaGa:La:S Fabrication Technology:La:S Fabrication Technology

Rods, Canes and FibersRods, Canes and Fibers

Multimode FiberMultimode Fiber Single-mode FiberSingle-mode Fiber

Holey FiberHoley Fiber Planar WaveguidePlanar Waveguide

GaGa:La:S -based glasses for photonic:La:S -based glasses for photonicapplications: state of the artapplications: state of the art

�� GaGa:La:S glass:La:S glass (fibre amplifiers & lasers)(fibre amplifiers & lasers)•• 65Ga65Ga22SS33:30La:30La22SS33:5La:5La22OO33 “low oxide” composition. “low oxide” composition.•• Low phonon energy host for active rare earths (Pr, Low phonon energy host for active rare earths (Pr, DyDy, , ErEr, Tm, ...)., Tm, ...).•• Glass stability upon reheating ( Glass stability upon reheating (devitrificationdevitrification) is an issue.) is an issue.•• Single mode fibre achieved, although only in short lengths and poor quality. Single mode fibre achieved, although only in short lengths and poor quality.

�� GaGa:La:S:O glass :La:S:O glass (nonlinear devices, (nonlinear devices, microstructuredmicrostructured fibers) fibers)•• 78Ga78Ga22SS33:22La:22La22OO33 “oxysulphide” composition. “oxysulphide” composition.•• Better thermal stability makes fibre drawing easier. Better thermal stability makes fibre drawing easier.•• Lower Lower QEs QEs of rare earth ions, but nonlinearity as high as in of rare earth ions, but nonlinearity as high as in GaGa:La:S.:La:S.•• Multimode fibers pulled in hundred meter lengths. Holey fibre demonstrated. Multimode fibers pulled in hundred meter lengths. Holey fibre demonstrated.

Current Limitation: High LossCurrent Limitation: High Loss

Sources of Optical LossSources of Optical Loss•• Impurities (Fe3+, ...).Impurities (Fe3+, ...).•• Scattering (Crystals, ...)..Scattering (Crystals, ...)..•• Core/clad interface defects.Core/clad interface defects.•• Weak Tail.Weak Tail.

Target for a Practical Device:Target for a Practical Device: 1 dB/m Single Mode Fibre 1 dB/m Single Mode Fibre ((��22��m core diameter)m core diameter)

Scattering

Fe3+

Absorption

OH-

Absorption

Lowest Loss UncladFibre to date:

2.5dB/m @ 1.5�m 1 dB/m @ 4�m

WAT in WAT in ChalcogenideChalcogenide Glasses Glasses

• Typical of covalentChalcogenide Glasses(As2S3, GeS2,...).

• Limits intrinsically the NIRglass transparency to�1 dB/m.

• Caused by additionalelectron. states in thebandgap.

(Defects, Disorder)WAT in AsWAT in As22SS33 glass glass

•• Is there a Weak Tail in Is there a Weak Tail in GaGa:La:S?:La:S?

•• What is the What is the Transparency LimitTransparency Limit of of GaGa:La:S ?:La:S ?

•• Is it feasible to fabricate optical devicesIs it feasible to fabricate optical devices

based on this glass system?based on this glass system?

Key issues:Key issues:

Measurement of Low Levels ofMeasurement of Low Levels ofAttenuation in High Index Media.Attenuation in High Index Media.

L � 1cm

I0

R � 28.9%T � 70.9%

� � 2��+ �L � 0.2%

� Assuming n � 2.4 &������1dB/m (no scattering considered).

Ga:La:S

Why is conventional “transmission”Why is conventional “transmission”measurement hard?measurement hard?

� High refractive index causes a big Fresnel Loss

(two orders higher than Bulk Absorption).

� Inhomogeneity in thick samples.

� Interference effects in thin samples.

� Beam defocussing and steering in UV/VIS

and FTIR spectrometers.

� Cannot distinguish scattering from absorption.

Laser CalorimetryLaser Calorimetry

• Direct Measurement ofthe Bulk Absorption.

• High sensitivity.

• Independent onScattering.

• Can discriminate bulkfrom surface absorption.

•• Which source?Which source?

� �TdtdCAI p ��0

Why using the FEL atWhy using the FEL atJefferson Labs ?Jefferson Labs ?

� Tuning Range.

� High average Power.

� Ability to change the peak power while

maintaining constant the average power.

� Beam Quality.

Setup: CalorimeterSetup: Calorimeter

• Vacuum Chamber.• Additional Ext. Shielding.• Sample Mount.• Signal Feedthrough.• Vacuum connections.• Silica WF ‘Front’ Window.

• CaF2 Brewster ‘Back’Window.

• Gas Inlet for ThermalRe-Equilibration.

Sample MountSample Mount• Low Thermal Leakage.• Steady, Low Thermal Capacity.• Conduction sample-sensors.

Sensors & WiringSensors & Wiring• Pt film RTDs (8).• Th. conductive vacuum epoxy.• Cu wiring (0.07mm), PTFE coated.

Temperature monitoring Temperature monitoring• Four Wire Method.• Control of Thermal emfs.• Keithley 2000, PC-interfaced

Setup: Sample Mount & Setup: Sample Mount & RTDsRTDs

Setup: Optical PathSetup: Optical Path

M ��4.3���25mm

���3mm

Higher order HarmonicsFilter (Si Brewster’s window)

To Keithley 2000

Sample

Chamber Temperature RTD monitor

Beam Dump

Optical Power Meter

CaF2 Brewster’s back window

Heating CurvesHeating Curves

Pulsed method:Pulsed method:

��T(t)=T(t)=��QQ//mcmcpp(e(e-t/-t/����- e- e-t/-t/��))

�����: absorbance (� � �L+2�). Q: P0 �tpulse.mcp: total heat capacity (sample + holder)�����: rise time const.�����: decay time const.

0.00

0.25

0.50

0.75

1.00

1.25

0

10

20

30

40

50

0 100 5 103 1 104 1.5 104

0 0.5 1 1.5 2 2.5 3 3.5 4

Tem

pera

ture

Incr

ease

�T

(ºC

)

Laser Pow

er (W)

Time (s)

( hrs )

0.0

0.1

0.2

0.2

0.3

0.4

0.5

0 2 103 4 103 6 103 8 103 1 104

@ 1.55�m, 37MHz, 2kJ@ 1.55�m, 74MHz, 2kJ@ 1.7�m, 37MHz, 2kJ

Time (s)

Nonlinear and wavelength effectNonlinear and wavelength effect

0.0

0.2

0.3

0.5

0.6

0

10

20

30

40

50

0.0 5.0 103 1.0 104 1.5 104

Experimental Data

Fit Curve 1st Heating

Fit Curve 2nd Heating

Fit Curve 3rd Heating

Laser Power

Tem

pera

ture

Incr

ease

�T

(ºC

)

Transmitted Laser P

ower (W

)

Time (s)

1.9±0.2 kJ@ 1.55�m

37MHz

1.9±0.3 kJ@1.7�m37MHz

2.0±0.3 kJ@1.55�m

74MHz

Absorption vs. Pulse Rep. Rate

• Fixed wavelength:���= 1.55�m

• �(I) = �0 + �1I

• No evidence ofnonlinear absorption

0.000

0.005

0.010

0.015

0.020

0.025

0.030

18 36 54 72

Ga:La:S glass [65:30:5]Ga:La:S:O glass [78:22]

Abs

orpt

ion

coef

ficie

nt �

(cm

-1)

Pulse Repetition Rate (MHz)

Absorption vs. Sample ThicknessAbsorption vs. Sample Thickness

� 02.1 ± 0.2Ga:La:S:O

� 01.2 ± 0.1Ga:La:S

��

(10-2 cm-1)0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 2 103 4 103 6 103 8 103 1 104

0 1 2 3

Tem

pera

ture

Incr

ease

�T

(ºC

)

Time (s)

( hrs )

L = 2.0mm

L = 3.2mm

L = 8.5mm � = 1.55�m

�tpulse = 150sQ = 1KJ

0.005

0.010

0.015

0.020

0.025

0.0 0.2 0.4 0.6 0.8 1.0

Ga:La:S glass [65:30:5]

Ga:La:S:O glass [78:22]

Abs

orba

nce

Thickness L (cm)

� �� �� L + 2�

�

ResultsResults

•• Calorimetric Measurements of Optical Absorption of two sets ofCalorimetric Measurements of Optical Absorption of two sets ofsamples (samples (GaGa:La:S and :La:S and GaGa:La:S:O compositions) have been:La:S:O compositions) have beenperformed at 1.55performed at 1.55��m and 1.7m and 1.7��m wavelengths.m wavelengths.

•• The Bulk Absorption is in the region of 10The Bulk Absorption is in the region of 10-2-2cmcm-1-1 and is the and is theprincipal mechanism of optical loss at both the wavelengths. Noprincipal mechanism of optical loss at both the wavelengths. Noevidence of surface absorption results from our measurements.evidence of surface absorption results from our measurements.

•• No evidence of nonlinear absorption was found.No evidence of nonlinear absorption was found.

•• Our measurements also allow to establish a lower limit to theOur measurements also allow to establish a lower limit to thedamage threshold in damage threshold in GaGa:La:S glasses, that is 14W Average CW:La:S glasses, that is 14W Average CWPower with 0.2KW/cmPower with 0.2KW/cm22 Power Density (>6MW/cm Power Density (>6MW/cm22 Peak). Peak).

Conclusions and further workConclusions and further work

•• The value of absorption is higher than expected, but stillThe value of absorption is higher than expected, but stillcompatible with the fabrication of short in-fibre and planarcompatible with the fabrication of short in-fibre and planarwaveguide devices.waveguide devices.

•• Additional Measurements at different wavelengths are requiredAdditional Measurements at different wavelengths are requiredto assess if the absorption is due to impurities or to a Weak Tail.to assess if the absorption is due to impurities or to a Weak Tail.

•• CharacterisationCharacterisation of nonlinear properties vs. the of nonlinear properties vs. the wavelenghtwavelenghtby the z-scan technique.by the z-scan technique.

•• Many other interesting glass systems yet to be investigated....Many other interesting glass systems yet to be investigated....

AcknowledgementsAcknowledgements

D.W. Hewak E.G. Webb A. Favre E.J. Tarbox K.E. Frampton T.C. AustinR.C. Moore M.R. Long

Project funding and sponsorshipProject funding and sponsorship::UK Engineering and Physics Sciences Research Council UK Engineering and Physics Sciences Research Council (EPSRC)(EPSRC)and and Pirelli Pirelli CaviCavi e e SistemiSistemi..

�� ORC and ECS, University of Southampton: ORC and ECS, University of Southampton:

�� Jefferson Laboratories: Jefferson Laboratories:

The entire JLABS team !!!The entire JLABS team !!!