Mechanical, Optical and Electrical Properties of Nano-polished CVD Diamond Films

Department of Electronic Devices

J.A. Weima Mechanical, Optical and Electrical Properties of Nano-polished ...

Mechanical, Optical and Electrical

Properties of Nano-polished CVD

Diamond Films

J. A. Weima1), J. von Borany2), and W. R. Fahrner1)

1) Department of Electronic Devices, University of Hagen,

Haldener Str. 182, D-58084 Hagen, Germany2) Institute of Ion Beam Physics and Materials Research

P.O. Box 510119, D-01314 Dresden, Germany



Contents

1. Introduction

2. Description of the polishing machine

3. Experimental results:

(i) SEM and AFM images of as-grown,

polished and beveled surfaces

(ii) Carbon phases and optical centers

determined by Raman spectroscopy

(iii) CL Spectra

(iv) ERDA depth distribution of carbon

(v) RBS determination of surface

contaminants

(vi) I-V and EL spectra of polished CVD

diamond films

4. Summary and Conclusion



Introduction:Polishing procedure:

i) CVD diamond films polished on transition metals (steel)

ii) Ambient Atmosphere; mixture of hydrogen-argon

(4% - 96%), ambient temperature (700-950 °C), pressure

exerted on the diamond film (1-2 kPa), velocity of the

polishing plate (1-3 cm/s), frequency and amplitude of

the transversal vibrations

Applications:

Thermal management, optical windows, wear tools, micro-

surgical equipment, electronic and opto-electronic devices

Motivation:

i) Investigating various non-diamond carbon phases, carbon

dissolution in steel: Model of thermochemical polishing

ii) Investigating optical centers and contaminants and their

location on the polished diamond surfaces: Enhancement

of defect free device fabrication

iii) Comparative study of I-V characteristics of polished and

unpolished CVD diamond films: Effect of polishing on

performance of diamond-base devices



The Thermochemical Polishing Machine

Diamond Sample

ScanningThermometer

Thermo-Couple

Gas Inlet

Chamber

Hot wire-Tungsten

WaterInlet

DriveBoard

FrequencyGenerator

Cover forChamberMain

PowerSupply Heat

Reflectors

Ceramic

Motor

PowerSupply

WaterOutlet

AdditionalDrive Board

PowerSupply

DriveBoard

Weight

Motor

PolishingPlateFrequency

Generator


J.A. Weima Me

SEM micrograph of growth side of an as-grown CVDdiamond film x 200

chanical, Optical and Electrical Properties of Nano-polished ...

Grain boundaries



SEM micrograph of the growth side of a polished CVDdiamond film x 5000



AFM image of the growth side of a polished optical gradeCVD diamond film Ra = 1.3 nm

AFM image of the substrate side of a polished opticalgrade CVD diamond film, Ra = 1.5 nm



An SEM image of a diamond CVD diamond filmbeveled successively on both sides at 15°. Thecutting edge with a radius of curvature of about50 nm is formed at the intersection of the twobeveled facets.



Mixed bonds arising from sp2 and sp3 bonded carbonsystem

Polished for 16 hours: The broad band splits intothe nanocrystalline graphite and the amorphouscarbon bands.

1000 1200 1400 1600 18006x103

7x103

8x103

9x103

1x104

1x104

1x104

Inte

nsity

[arb

. uni

ts]

Wave number [cm-1]

1000 1200 1400 1600 18006x103

7x103

8x103

9x103

1x104

1x104

1x104

1206

Broad non-diamond carbon band

1331In

tens

ity [a

rb. u

nits

]

Wave number [cm-1]



Further polishing: The microcrystalline graphiteband appear in addition to the previous bands.

Further polishing: The entire diamond surface isnow covered only by the two graphite bands.

1000 1200 1400 1600 18002,0x103

4,0x103

6,0x103

8,0x103

1,0x104

1,2x104

1,4x104

1,6x104

1,8x104

1331 1580

14781353

Inte

nsity

[arb

. uni

ts]

Wave number [cm-1]

1000 1200 1400 1600 18000

1x103

2x103

3x103

4x103

5x103

6x103

1580

1353

Nanocrystalline

graphite

M icrocrystalline

graphite

Inte

nsity

[arb

. uni

ts]

Wave number [cm-1]



Polishing at low temperature (800 °C): The non-diamond carbon dissolves into the metal.

Final polishing at much lower temperature (750°C): The entire diamond surface is free of non-diamond carbon phases

1000 1200 1400 1600 1800-1,0x103

0,0

2,0x103

4,0x103

6,0x103

8,0x103

1,0x104

1,2x104

1,3x104

1578

1331In

tens

ity [a

rb u

nits

]

Wave number [cm-1]

1000 1100 1200 1300 1400 1500 1600 1700 1800

0,0

2,0x103

4,0x103

6,0x103

8,0x103

1,0x104

1,2x104

1,4x104 1331 cm-1

Inte

nsity

[arb

. uni

ts]

Wave number [cm-1]



Raman spectra of a thermochemically polished optical grade

CVD diamond film. Low frequency Raman lines (100-700

cm-1) are seen for the first time. The lines are tentatively

attributed to clusters of carbon particles left on the polished

surfaces.

200 400 600 800 1000 1200 1400 1600-1,0x103

0,0

5,0x103

1,0x104

1,5x104

2,0x104

1580

1352

657585

485

392

280215

Inte

nsity

[cou

nts]

Wave number [cm-1]



Raman spectra of an as-grown CVD diamond film taken atthree different spots. The spectra show the diamond Ramanline, the nitrogen-vacancy defect centers and the silicon-vacancy defect center.

0 1000 2000 3000 4000 5000 6000

1.6x104

1.2x104

8.0x103

4.0x103

0.0

diamond-Raman line1332

Si-V band

N-V- band

N-V0 bond

5894

37742068

Inte

nsity

[cou

nts]

Wave number [cm-1]



Raman spectra of a polished CVD diamond film taken at threedifferent spots. In addition to the bands seen in the as-grownfilm, bands of nanocrystalline graphite, microcrystallinegraphite, nitrogen molecules, and hydrogen molecules are alsoobserved.

0 1000 2000 3000 4000 5000 6000

0

1x103

2x103

3x103

4x103

5x103

N2

Diamond

lineH2

N-V- Si-V N-Vo

Graphite bands

C-Hn vibrations

Inte

nsity

[cou

nts]

Wave number [cm-1]



RT CL spectra of (a) mechanical grade (b) optical grade CVDdiamond films. The spectra contain bands attributed to theblue band-A, N-V complexes and Si-V complexes.

200 300 400 500 600 700 800 900

0

20

40

60

80

100

120

Energy [eV]1.41.61.82.12.53.14.16.2

Si-V band

N-V band

A band

Inte

nsity

[arb

. uni

ts]

Wavelength [nm]

200 300 400 500 600 700 800 900

5

10

15

20

25

30

Energy [eV]1.41.61.82.12.53.14.16.2

Si-V band

N-V band

Blue band-A

Inte

nsity

[Arb

. uni

ts]

Wavelength [nm]



(a) (b)

(c) (d)

(e)

SEM-SE and the monochromatic 438 nm, 605 nm, 845 nm CLimages of an as-grown CVD diamond film showing the regionsof luminescence.

200 300 400 500 600 700 800 9000

50

100

150

200

2nd Order blue band-A

N-V band

blue band-A

Energy [eV]1.381.552.07 1.772.483.104.146.20

Inte

nsity

[%]

Wavelength [nm]



0 50 100 150 200 250 3000,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8ERDA: 35Cl7+, 35 MeV

Polishing Plates(1.220 /115CrV3)

Process Time virgin 0,5 h 1,0 h 4,0 h 8,0 h

carb

on c

once

ntra

tion

(x10

23cm

-3)

depth (nm)

0

10

20

30

40

50

60

70

80

90

car

bon

cont

ent (

at.-

%)

ERDA carbon depth profiles in steel measured for polishingtimes between 0-8 hours. The profiles clearly confirm thedissolution of carbon in steel during the polishing.



0 50 100 150 200 250 3000,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8ERDA: 35Cl7+, 35 MeV

Polishing Plates(1.220 /115CrV3)

virgin S1: 8h S2: 8h S3: 8h

carb

on c

once

ntra

tion

(x10

23cm

-3)

depth (nm)

0

10

20

30

40

50

60

70

80

90

car

bon

cont

ent (

at.-

%)

ERDA carbon depth profiles in three steel plates on whichCVD diamond films were successively polished for 8 hours.An non-homogeneous distribution of carbon is observedespecially in the first 50 nm from the surface.


J.A. Weima Mechanical, Optical and Electrical Properties of N

Determination of D(x,t) by fitting experimental restheoretical values.

+−−∞= ietNxNtxN **),0()140/exp(1),( π

Calculated value: D(x,t) = 1.16 x 10-14 cm2/s.

0 50 100 150 200 250

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

D = 1.16 x 10-14 cm2s-1 0 hour calculated 0 hour experiment 4 hours calculated 4 hours experiment 8 hours experiment 8 hours calculated

Con

cent

ratio

n x

1022

[cm

-3]

Depth [nm]

ano-polished ...

ults to

Dtxrfc

2

300 350


J.A. Weima Mechanical, Optical and Electrical Properties of N
ano-polished ...



Experimental and simulated RBS spectra of the surface of aCVD diamond film thermo-chemically polished on steel at950 °C for 8 hours. Iron found at depths within 120 nm fromthe surface is the only detectable contaminant.

Fe



200 300 400 500 600 700 8000

50

100

150

200

2501.73 / 20

FZ R

osse

ndor

f: G

rötz

sche

l / v

on B

oran

y, 7

.03.

00

Simulation:Lay 1: d = 40 nm C:Fe=99.2:0.8Lay 2: Bulk C=100

1.7 MeV, 4He+

10 µC, 0°, rs

Samples: FU Hagen, ElektrotechnikCVD-Diamond, Nanopolished: 25 h, 950°CSubstrate side

D2: as polished D3: polished + etched D2 - Simulation

RB

S y

ield

channel number

0,4 0,6 0,8 1,0 1,2 1,4

energy (MeV)

Experimental RBS spectra of two CVD diamond filmspolished at 950 °C for 25 hours each. The as-polished filmcontain iron at depths within 40 nm from the surface is theonly contaminant. The film etched in chromic acid is virtuallyfree from iron contaminants.

Fe



RT and 300 °C I-V characteristics of p-i-n, p-i-p and n-i-ndiodes with L=5 µm fabricated on a thermochemicallypolished CVD diamond film. The RT leakage current of the p-i-n diode is smallest while that of the p-i-p is about an orderhigher. Moreover, the forward current of the p-i-n diode isabout 2 orders of magnitude higher than those of the p-i-p andn-i-n diodes.

0,1 1 10 100 10001x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

1x10-2

p-i-n RT p-i-p RT n-i-n RT p-i-n 300 °C p-i-p 300 °C n-i-n 300 °C

Cur

rent

[A]

Voltage [V]



The I-V characteristics at 300 °C of p-i-n diodes with thei-region varying from 3-10 µm showing both the forward andreverse bias regimes. A comparison of the current values atforward and reverse biases of 60 V shows that the forwardbias current is 1.8, 2.4, 2.8 and 3.6 orders of magnitude higherthan the reverse bias current for L = 3, 5, 8 and 10 µm,respectively.

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

1x10-2

CVD diamond-base p-i-n diodes

p-i-n (3µm) 300 °C p-i-n (5µm) 300 °C p-i-n (8µm) 300 °C p-i-n (10µm) 300 °C

Cur

rent

[A]

Voltage [V]



Current-voltage characteristics of a p-i-n diode with L=8 µm.The asymmetric trend of the curves is due to the difference inthe forward and reverse bias currents of the p-i-n diode.

-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 1201x10-14

1x10-12

1x10-10

1x10-8

1x10-6

1x10-4

1x10-2

p-i-n diode: L = 8 µmn common

T=RT T=50 °C T=100 °C T=150 °C T=200 °C T=250 °C T=300 °C

Curre

nt [A

]

Voltage [V]



Current-voltage characteristics of a p-i-p diode with L=10 µm.The symmetric trend of the curves is due to successiveinjection of carriers across the p-i junctions of the identicallydoped p-regions of the p-i-p diode. The I-V characteristicsholds for n-i-n diodes as well.

-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 12010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

p-i-p diode: L = 10µm

T=RT T=50 °C T=100 °C T=150 °C T=200 °C T=250 °C T=300 °C

Cur

rent

[A]

Voltage [V]



EL spectra of CVD diamond-base p-i-p, p-i-n and n-i-n diodesfabricated on a thermochemically polished CVD diamondfilm. A blue band-A at 2.85 eV is attributed to dislocationsand a red band at 1.84 eV is attributed to the recombination ofdonor-acceptor pair.

350 400 450 500 550 600 650 700 7502

4

6

8

10

12

14

16

18

20

22

Red band

Blue band-A

Electron Energy [eV]1.651.771.912.072.262.482.763.103.55

p-i-p; 0.2 mA - 305 V n-i-n; 0.2 mA - 280 V p-i-n; 0.2 mA - 260 V

EL in

tens

ity [a

rb. u

nits

]

Wavelength [nm]



EL spectra of a p-i-n diode with L = 8 µm taken at increasingcurrent and voltages. The maximum of the blue band-A isconstant at about 2.85 eV and its intensity increases linearlywhereas the intensity of the red band is saturated.

350 400 450 500 550 600 650 700 750

10

20

30

40

50

60

Electron Energy [eV]

Red band

Blue band-A

1.651.771.912.072.262.482.763.103.55

0.2 mA - 280 V 0.4 mA - 490 V 0.6 mA - 540 V

EL in

tens

ity [a

rb. u

nits

]

Wavelength [nm]



RT I-V characteristics of p-i-p diodes fabricated on (a): athermochemically polished CVD diamond film and (b): an as-grown CVD diamond film. The I-V curves of the polish filmare more diode-like than those of the unpolished film.

0,1 1 10 100 10001x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

FP-SCLC regime

FP-TE regime

Trap filling regime

p-i-p diodes on a polishedCVD diamond film RT: ~23 °C

L=5 µm L=7.5 µm L= 10 µm

Cur

rent

[A]

Voltage [V]

0,1 1 10 100 10001x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

p-i-p diodes on an unpolished CVD diamond filmTemp: ~ 23 °C

L=5 µm L=7.5 µm L=10 µm

Cur

rent

[A]

Voltage [V]



RT I-V characteristics of n-i-n diodes fabricated on (a):polished and (b): unpolished CVD diamond films. Theleakage current of the unpolished film is about 2 orders ofmagnitude higher.

0,1 1 10 100 10001x10-14

1x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

n-i-n diodes on a polishedCVD diamond filmTemp: ~ 23 °C

L=5 µm L=7.5 µm L=10 µm

Cur

rent

[A]

Voltage [V]

0,1 1 10 100 10001x10-14

1x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4n-i-n diodes on an unpolished CVD diamond filmTemp: ~ 23 ° C

L=5 µm L=7.5 µm L=10 µm

Cur

rent

[A]

Voltage [V]



Summary and Conclusion

(1) Carbon phases include nano- and microcrystalline

graphite, amorphous carbon; Complexes include

C-Hn, H2 and N2 complexes

(2) Best AFM Surface roughness result 1.3 nm

(3) Dissolution of carbon in steel confirmed by depth

profiles: Diffusion constant of 1.16 x 10-14 cm2s-1

(4) Optical centers include Si-V, N-V0, N-V-1 and blue

band-A found in the CL and EL spectra as well

(5) Iron is the only detectable surface contaminant

(6) (i) Photolithography is effectively achieved only

on nano-polished surfaces

(ii) The leakage current of diodes on unpolished

diamond is about 2 orders of magnitude

higher

(iii) p-i-n diodes deliver highest current at higher

voltages in comparison to p-i-p and n-i-n.

(iv) The ratio of the forward to reverse bias

current increases with increasing L for the

measured diodes.

Mechanical, Optical and Electrical Properties of Nano-polished CVD Diamond Films

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