GINT samples as metal -insulator -semiconductor (MIS) diodes · 14/01/2008 GINT coll. Meeting...

14/01/2008 GINT coll. Meeting 14/01/2008 A. Di Bartolomeo 1

GINT samples as GINT samples as

metalmetal--insulatorinsulator--semiconductor semiconductor

(MIS) diodes (MIS) diodes

Gruppo di SALERNOGruppo di SALERNO

Gruppo di Napoli

Gruppo dell’Aquila


Measurements on Si substrate• Si substrate used for CNT films

– p-type ?

– = 1- 40 cm

– NA=(4 - 10)·1014 /cm3

– Native oxide ~ 20 A

• Two-point probe measurements

– side-to-side (planar)

– top-down (vertical)

– pressure on the tips to brake the SiO2 barrier

– Effects of SiO2• Dark current reduction• tunnelling with negative resistance

in I-V curves

Si~ 500 µm

~ 20 A

SiO2

V

A

planar probeconfiguration

vertical probe configuration

Metal-Semiconductor-Metal MSM

Metal-Insulator-Semiconductor-Insulator-Metal MISIM

(often used as photodetector)

2 mm


• Contacts: Schottky - Schottky

• Contacts: Ohmic – Schottky

• Contacts: Ohmic - Ohmic

Expected I-V behaviour of MSM

I

V

-

Met

p-Si

+forward

bias

hole current

qIVapplI

+

Met

p-Si

- reverse

bias

hole current

qIVapplI

Caso ideale

+

-

-

+

MSM structures

as two

back-to-back

Schottky diodes

I

V

I

V

Si~ 2 mm

V

A (1)

(2)

(1) S

-(2

) O

(1) O

-(2

) S

I

V

+

-

Caso ideale


-3 -2 -1 0 1 2 3

-1,00x10-6

-7,50x10-7

-5,00x10-7

-2,50x10-7

0,00

2,50x10-7

5,00x10-7

7,50x10-7

1,00x10-6

Cu

rre

nt (A

)

Voltage (V)

Schottky-Schottky contacts

R-3v~ 23 M R3v~ 7 M

-3 -2 -1 0 1 2 3

1,0x10-8

1,0x10-7

1,0x10-6

Cu

rre

nt (A

)

Voltage (V)

1e-6

Si~ 2 mm

V

A (Sch)

(Sch.)

1e-6

Asymmetry due to a difference in the diode characteristics,

as area, SiO2 barrier, etc

+-


Schottky-ohmic contacts

• one Schottky (1) and one Ohmic (2) contact

• Red and black curves obtained with swapped probe polarity

• Rectifying Schottky diode symmetrical for voltage inversion

-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0

1E-7

1E-6

1E-5

Cu

rre

nt

(I)

Voltage (V)

probes AB

swapped probes BA

1e-5 R3V = 23 M

-10,0 -7,5 -5,0 -2,5 0,0 2,5 5,0 7,5 10,0

-1,0x10-5

-8,0x10-6

-6,0x10-6

-4,0x10-6

-2,0x10-6

0,0

Cu

rre

nt

(A)

Voltage (V)

R-3V = 3,4 M

-1e-5

- +

Si~ 2 mm

V

A (Sch)

(Oh.)


Ohmic-ohmic contacts

-3 -2 -1 0 1 2 3

-1,5x10-4

-1,0x10-4

-5,0x10-5

0,0

5,0x10-5

1,0x10-4

1,5x10-4

Cu

rre

nt (A

)

Voltage (V)

-3 -2 -1 0 1 2 3

10-5

10-4

Cu

rre

nt (A

)

Voltage (V)

<R> = 20 ± 3 k

1e-4

+-

Si~ 2 mm

V

A (Oh.)

(Oh.)

1e-4

Low resistance and

V-symmetric behaviour


e-h photo

generation

Light on MS or MIS structure• MSM structure used as photodetector

– particularly efficient for visible and ultraviolet light

– < c = 1.24/Eg µm

– Effective absorption length ~1 µm

• for Schottky diode relative photocorrent higher for reverse bias

– no barrier to cross

– lower recombination rate

– a thin layer of oxide helpful to get higher relative photocurrent

• for ohmic contacts, photocurrent about the same for forward and reverse bias

-

Met

p-Si

+forward

bias

+

Met

p-Si

- reverse

bias

further reduced reverse current

SiO2

h

+

Met

p-Si

- reverse

bias

reverse current

h

forward current

h


Light on Si with Schottky-Ohmic cts

-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5C

urr

en

t (A

)

Voltage (V)

dark

light on/off

dark-better contacts

light on/off-better contacts

MOS (Metal-Oxide-Semiconductor)

diode with high photocurrent by illumination with a 40W white lamp

and reverse bias:

Iph =(ILight – Idark) ~ 100 Idark

No SiO2

barrier

SiO2

barrier

-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

0,0

0,5

1,0

1,5

2,0

I (

Lig

ht -

Da

rk)

/ D

ark

Voltage (V)

-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

-20

0

20

40

60

80

100

120

140

I (L

ight -

Dark

) / D

ark

Voltage (V)

Iph= (ILight – IDark) ~ 1 to 2 IDark

1e-6

The increase of photocurrent at low bias is due to the expansion of the depletion region in the reverse biased Schottky junction

-

+


Remarks:

I-V characteristics of a MSM structure depends on the contact type.

A MISM (with one Schottky and one Ohmic contact) is a very efficient

photodetector, with high reverse photocurrent;

that could be exploited to enhance the photocharge of a CNT based device.

Warning:

Contacts to our Si samples are very critical and sensitive: they can introduce

new devices or make non reproducible measurement.

The contact issue should be addressed with great attention in our future

sample production!

-

+


Measurements on MIS structures with and without

carbon nanotubes


Photocurrent on vertical MSM with CNT

-9 -6 -3 0 3

-1,00x10-6

-7,50x10-7

-5,00x10-7

-2,50x10-7

0,00

2,50x10-7

5,00x10-7

7,50x10-7

1,00x10-6

dark

lab light on CNT

lamp light on CNT 40 cm


dark

lab light on back

lamp light on back 40 cm


Curr

en

t (A

)

Voltage (V)

Silicon Si3N4

V

A

AuPt

-6 -4 -2 0 2 4

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

Light on CNT

Light on substrate (back)

dark

Cu

rre

nt (A

)

Voltage (V)

dark

lab light on CNT



dark

lab light on back



-

+

(1)

(2)

Si3N4 thickness unknown: 50-70 nm?

Highly doped Si (unknown level and type)

-8 -6 -4 -2 0

-4,0x10-8

-3,0x10-8

-2,0x10-8

-1,0x10-8

0,0

1,0x10-8

2,0x10-8

3,0x10-8

4,0x10-8

dark

lab light on CNT



dark

lab light on back



Cu

rre

nt

(A)

Voltage (V)


-

Met p-Si

Si3N4

h

+

Met

CNT

Si3N4

(1) (2)

Vappl

Photocurrent on vertical MSM with CNT

Silicon

V

A

(1)

(2)

-5,0 -2,5 0,0 2,5 5,0

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

Ph

oto

cu

rre

nt

(A)

Voltage (V)

Light on back

quasi-ohmic contact

Tunnelling voltage through barrier (2)

Higher electric field at interface (1)

higher photocurrent from back

Likely ohmic contact because of Pt

+

Met

p-Si

Si3N4

h

-

Met

CNT

Si3N4

(1) (2)

Vappl


CNT on Si3N4-Si with light (s1)

-20 -15 -10 -5 0 5

-4,0x10-4

-3,0x10-4

-2,0x10-4

-1,0x10-4

0,0

1,0x10-4

With CNT

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

dark

light

filter 1.2%

filter 2.7%

filter 4.7%

filter 6.7%

filter 9.9%

filter 15.1%

filter 19.2%

filter 25.2%

filter 50.2%

filter 62.5%

filter 79.8%

filter 97.1%

light

Silicon Si3N4

V

A

AuPt

-20 -15 -10 -5 0 5

-4,0x10-4

-3,0x10-4

-2,0x10-4

-1,0x10-4

0,0

1,0x10-4

Without CNT

Mea

su

red

Cu

rre

nt (A

)

Applied Voltage (V)

dark

light

filter 79.8% filter 62.5%


filter 15.1%

filter 6.7%

Silicon Si3N4

V

A

AuPt

• Qualitatively same behaviour with and w/oCNTs:

1. w/o CNTs lower contact area and reduced photocharge collection

2. With CNTs additional photo-charge is created and collected.

Dark

Light

Dark

Light

Filter on light

intensity

lamp

I - filter

lamp

I - filter

CNTs

No CNTs


CNT on Si3N4-Si with light (s2)

-10 -8 -6 -4 -2 0 2

-1,0x10-5

-5,0x10-6

0,0With CNT

Curr

en

t (A

)

Voltage (V)

dark

light

filter 1.2%

filter 2.7%

filter 4.7%

filter 6.7%

filter 9.9%

filter 15.1%

filter 19.2%

filter 25.2%

filter 50.2%

filter 62.5%

filter 79.8%

filter 97.1%

light

-10 -8 -6 -4 -2 0 2

-1,0x10-5

-8,0x10-6

-6,0x10-6

-4,0x10-6

-2,0x10-6

0,0

Without CNT

Cu

rre

nt (A

)

Voltage (V)

dark

light filter 79.8%



filter 6.7%

With CNT higher reverse current, lower resistance.


Ex. MIS tunnel diode on p++-Si

Efm

Eg

M I S

Efs

qVc

qVv

Efm

Eg

positive bias

+ - (2)

Efs

negative bias

- +

negative bias

- +

Efm

Eg

Efs

Efm

Eg

Efs

negative bias

- +

EfmEg

Efs

(a) (b) (c) (d)

V

I(a)

(b)

(c)

(d)

Pt on Si can create a hole accumulation at Si - Si3N4

and make silicon degenerate due to high workfunction (5.7 eV vs

si = 4.05 eV-10 -5 0 5

-5,0x10-6

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

Without CNT

Curr

ent (A

)

Voltage (V)

dark

light

filter 79.8%

filter 62.5%

filter 50.2%

filter 25.2%

filter 15.1%

filter 6.7%


CNT on Si3N4-Si with color light (s1)

Silicon Si3N4

V

A

AuPt

-14 -12 -10 -8 -6 -4 -2 0 2 4

-1,2x10-5

-1,1x10-5

-1,0x10-5

-9,0x10-6

-8,0x10-6

-7,0x10-6

-6,0x10-6

-5,0x10-6

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

1,0x10-6

2,0x10-6

no CNT

Me

asu

red

Cu

rren

t (A

)

Applied Voltage (V)

IDark

ILight1881nm

ILight1290nm

ILight1010nm

ILight846nm

ILight768nm

IDarkNoCNT

IDarkAfterNoCNT

ILight768nmNoCNT

ILight1104NoCNT

ILight1490nmNoCNT

with CNT

no CNTs

with CNTs

Silicon Si3N4

V

A

AuPt

• IV curves vs light for several wavelenghts

(881, 1290, 1010 etc nm)

• Wavelenghts close to the Si bandgap

(1100 nm) give higher reverse current!

• The sample with CNTs shows a higher

reverse current.

-filter

-filter


CNT on Si3N4-Si with color light (s1)

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3

-2,5x10-6

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

With CNTs

Me

asu

re C

urr

en

t (A

)

Applied Voltage (V)

Dark

Light 1881 nm

Light 1290 nm

Light 1010 nm

Light 846 nm

Light 768 nm

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3

-2,5x10-6

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

Dark

Dark after

Light 768 nm

Light 1104 nm

Light 1490 nm

CNTs removed

-14 -12 -10 -8 -6 -4 -2 0 2 4

-8,0x10-6

-7,0x10-6

-6,0x10-6

-5,0x10-6

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

1,0x10-6

2,0x10-6

W/o CNT

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

IDark

ILight1881nm ILight1290nm ILight1010nm ILight846nm ILight768nm IDarkNoCNT

IDarkAfterNoCNT ILight768nmNoCNT ILight1104NoCNT ILight1490nmNoCNT

With CNT

The sample with CNTs shows a higher reverse Current because of increased area and more Leaky insulating barrier

Are CNTs effective in collecting the charge photo-generated in silicon or they contribute

to photocharge?

Increased current for < 1100 nm

With CNTs

No CNTs

At 768 nm 8% current increase on both!

= 768 nm

A factor 4 increase on reverse current


-0,15 -0,10 -0,05 0,00 0,05 0,10 0,15

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

1,0x10-6

2,0x10-6

3,0x10-6

4,0x10-6

Y =-6,4E-7+2,6E-5 X

Cu

rre

nt

(A)

Voltage (V)

L1lab white lamp power 1 - lab

-0,15 -0,10 -0,05 0,00 0,05 0,10 0,15

-8,0x10-4

-6,0x10-4

-4,0x10-4

-2,0x10-4

0,0

2,0x10-4

4,0x10-4

6,0x10-4

8,0x10-4

Y =8,4E-8+0,0046 X

lab light (dark)

white lamp at 15 cm power 1

white lamp at 15 cm power 1

Cu

rre

nt

(A)

Voltage (V)

CNT’s on saffire

Resistance = 215 Ohm

No difference in the value of the resistance

under 3 different lighting conditions: laboratory

light (quite dark), microscope (white) lamp at power 1 and 3.

Photocurrent hidden by dark current

Photoconductance %:

(Slight - Sdark) / Sdark = 0,6 %

CNT growth at 500 C

8e-4

Saffire

A

V

AuPt

comb-to-comb pattern

3e-6


-0,04 -0,02 0,00 0,02 0,04

-1,0x10-5

-5,0x10-6

0,0

5,0x10-6

1,0x10-5

Y =-8,3E-9+2,2E-4 X

Cu

rren

t (A

)

Voltage (V)

Light Lab

White lamp 15 cm

CNTs on Si3N4-Si structure

• Before Si3N4 barrier cracking

– pad-to-pad resistance= 4.45 k

• Practically only current through CNT

p-Si Si3N4

VA

AuPt

CNT growth at 700 C

1e-5

100 W white lamp

Photoconductance % :(lamp distance 15 cm)

(Slight - Sdark) / Sdark = 1,2 %

Likely due to CNTs because lower current in Si in the voltage range

-0,04 -0,02 0,00 0,02 0,04

-1,00E-007

-5,00E-008

0,00E+000

5,00E-008

1,00E-007

1,50E-007

2,00E-007

Y =5,0E-8+2,7E-6 X

Pho

tocurr

ent (A

)

Voltage (V)

Light lamp 15 cm - lab

1e-7


Photoconductance % (lamp distance 15 cm):

(Slight - Sdark) / Sdark = 7.2 %

Si3N4-Si structure

p-Si Si3N4

VA

AuPt500 µm

100 nm

-10 -8 -6 -4 -2 0 2 4 6 8 10

-2,0x10-5

-1,0x10-5

0,0

1,0x10-5

2,0x10-5

R = 550 kOhm

Y =-2,5E-8+1,8E-6 X

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

light lab

white lamp 15 cm

white lamp 30 cm

Polynomial Fit of Data6_ILight2

-6 -4 -2 0 2 4 6

-6,0x10-7

-4,0x10-7

-2,0x10-7

0,0

2,0x10-7

4,0x10-7

6,0x10-7

Y =-3,5E-9+6,6E-8 X

Y =3,4E-9+1,01E-7 X

Pho

tocu

rre

nt

(A)

Voltage (V)

light lamp 15 cm - lab

white lamp 30 cm - lab

100 W white lamp

1e-5

6e-7

Sdark = 1.4 E -6 S


Conclusions:1. Measurement of I-V curves on several samples show

behaviours that might be explained in terms of Si-device properties (like MIS, Schottky, tunnel diodes, etc)

2. Attention for contacts and precise geometry in our samples needed

3. Hints for photoconductivity in CNTs, but very low conductance change!

4. Thicker and denser CNT samples needed to have more light absorption.

5. Design devices (MIS, MISIM etc) to amplify the CNT photocharge


MCNT thick film (2-300 m)

20 40 60 80 100 120

0,70

0,75

0,80

0,85

0,90

Model: Interrupted Metallic Conduction

Chi^2 = 0.00002

R^2 = 0.9903

P1 0.47708 ±0.00226

P2 112.56356 ±0.51601

P3 0.70542 ±0.00021

P4 0 ±0

P5 1 ±0

Linear fit

R = 0,65 + 0,0020 T

Resis

tan

ce (

Oh

m)

Temperature (°C)

T down

-0,010 -0,005 0,000 0,005 0,010

-0,010

-0,005

0,000

0,005

0,010

Cu

rre

nt (A

)

Voltage (V)

T = 140 °C

T = 65 °C

T = -40 °C

Study of R(T)

No GINT samples!


CNT film photoconductivity

50 60 70 80 90 100 110 120 130 140 150

0,755

0,760

0,765

0,770

0,775

0,780

0,785

0,790

Time (s)

Re

sis

tan

ce

(O

hm

)

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

Te

mp

era

ture

(°C)

0 100 200 300 400 500

0,755

0,760

0,765

0,770

0,775

0,780

0,785

0,790

Time (s)

Re

sis

tan

ce

(O

hm

)

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

Te

mp

era

ture

(°C)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

0,990

0,995

1,000

1,005

1,010

1,015

Time (Hour)

CN

T R

esis

tan

ce

(O

hm

)

22

23

24

25

26

27

28

Te

mp

era

ture

from

KT

-11

-6 (°C

)

No GINT samples!


Measurements on Measurements on

CNT / SiCNT / Si33NN44 / p/ p--Si structuresSi structures

in a 3in a 3--contact MOScontact MOS--like setuplike setup

Gruppo NAPOLI

Gruppo SALERNO


3-contact device

Si3N4 (th?)

AuPt

p-Silicon

VGS= 0

VDS

IDS

IGS

Meaurement conditions:

• bias on the gate -30 V < VGS < 30 V

• sweep -20V < VDS < 20V

• monitoring of IDS and IGS

I-V curves with and without laser light:

= 632 nmP = 2,3 mW 500 µm

2 cm

Source Drain

Gate

the back-gated metal-semiconductor-metal photodetector or BG-MSM for short.


No bias on gate

Si3N4

AuPt

p-Silicon

VDS

IDS

IGS

-20 -15 -10 -5 0 5 10 15 20

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

Y = 5,7 E-6 + 6,10 E-5 X

Drain-Source Voltage (V)

Dra

in C

urr

ent (A

)

R = 16,4 kOhm

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

No gate bias VGS

= 0 V

IGS

IDS

Light on CNTs

Gate

Curre

nt (A

)

Meaurement conditions:

• no bias on the gate VGS = 0• sweep -20V < VDS < 20V

• monitoring of IDS and IGS

I-V curves with and without laser light


Bias on gate

27

Si3N4

AuPt

p-Silicon

VGS

VDS

ID

IG

-20 -15 -10 -5 0 5 10 15 20

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

Y = 1,08 E-5 + 6,01E-5 X


Dra

in C

urr

en

t (A

)R = 16,6 kOhm

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

IGS

IDS

negative VGS

= -5 V

Light on CNTs

Ga

te C

urre

nt (A

)

-20 -15 -10 -5 0 5 10 15 20

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

Y = -1.58 E-5 + 6,55 E-5 X


Dra

in C

urr

en

t (A

)

R = 15,3 kOhm

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

IGS

IDS

positive VGS

= +5 V

Light on CNTs

Ga

te C

urre

nt (A

)

-20 -15 -10 -5 0 5 10 15 20

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

Y = 5,7 E-6 + 6,10 E-5 X


Dra

in C

urr

en

t (A

)

R = 16,4 kOhm

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

No gate bias VGS

= 0 V

IGS

IDS

Light on CNTs

Ga

te C

urre

nt (A

)

Vgs = 0V

Vgs = +5 V

Vgs = -5 V


Increased bias on gate

• Same effect as seen

before

-25 -20 -15 -10 -5 0 5 10 15 20 25

-2,0x10-3

-1,0x10-3

0,0

1,0x10-3

2,0x10-3

IGS

IDS

Light on CNTs

positive VGS

= +10 V

Ga

te C

urre

nt (A

)

Dra

in C

urr

en

t (A

)


-2,0x10-3

-1,0x10-3

0,0

1,0x10-3

2,0x10-3

-25 -20 -15 -10 -5 0 5 10 15 20 25

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

2,0x10-3

Light on CNTs

IGS

IDS


Dra

in C

urr

en

t (A

)

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

2,0x10-3

negative VGS

= -10 V

Ga

te C

urre

nt (A

)

Si3N4

AuPt

p-Silicon

VGS

VDS

ID

IG

Vgs = +10V

Vgs = -10V


Currents on 3-contact device

Current through CNT layer and Si:

ICNT + ISi = IDS - IGS

VGS = 0

+

-

p-Si

VDS < 0

IDS

IGS

ICNT

ISi

Accumulation or forward biased Schottky

p-Si

VGS = 0

VDS > 0

IDS

IGS

ICNT

-

+

ISi

Depletion or reverse biased Schottky

-20 -15 -10 -5 0 5 10 15 20

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

ICNT

+ ISi = current through CNT and Si

Y = 5,7 E-6 + 6,10 E-5 X


Dra

in C

urr

en

t (A

)

R = 16,4 kOhm

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

No gate bias VGS

= 0 V

IGS

IDS

Ga

te C

urre

nt (A

)(IDS - IGS) quasi - symmetric with respect to VDS < 0 as expected

for zero bias


Source-drain current through CNT/Si

Light reduces the R of silicon

î IGS increases (mainly for VDS <0).

î ISi increases (mainly for VDS <0).

VGSp-Si

VDS < 0

ICNT

ISi

Vdg = Vds - Vgs > 0 accumulation

Vdg = Vds - Vgs < 0 depletion

While sweeping Vds -20 ô 20 V

• Vgs > 0 î Accumulation Vds < Vgs

• Vgs < 0 î Accumulation Vds < Vgs

• Vgs = 25 V î Depletion only

The source barrier may be higher than the drain barrier

p-Si

VGS

VDS > 0

ICNT

ISi

Vgs > 0

-20 -15 -10 -5 0 5 10 15 20

-2,5x10-3

-2,0x10-3

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

I CN

T+

I Si

(A)

Drain-source Voltage (V)

Vgs = -25 V

Vgs = -15 V

Vgs = -10 V

Vgs = 0 V

Vgs = +10 V

Vgs = +15 V

Current S-D through CNT and Si:

ICNT + ISi


Source-drain current through Si (ISi)

VGS > 0

VDS > 0

IGS

ICNT

ISi

-20 -15 -10 -5 0 5 10 15 20

-3,0x10-3

-2,5x10-3

-2,0x10-3

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

I si

(A)


Vgs = 0 V dark

Vgs = 10 V dark

Vgs = 10 V light

Vgs = 15 V dark

Vgs = 15 V light

• Current ICNT + ISi at Vgs=-30 V

subtracted

• Si current higher for higher

bias because more

accumulation charge

• ISi steep increase due to Si3N4

barrier tunneling

• Si photoconductivity

VGS > 0

p-Si

VDS < 0

ISi

ICNT

Si3N4

barrier

Light on

Vgs > 0

-20 -15 -10 -5 0 5 10 15 20

-6,0x10-4

-4,0x10-4

-2,0x10-4

0,0

I si

(A)


Vgs = 0 V dark

Vgs = 10 V dark

Vgs = 10 V light

Vgs = 15 V dark

Vgs = 15 V light


S-d current through CNT+Si (ICNT + ISi)

VGS< 0

VDS > 0

ICNT

ISi

• Photocurrent can be due to

CNT and Si

• Shape of the photocurrent

suggests:

Si effect!

VGS < 0

p-Si

VDS < 0

ISi

ICNT

Vgs < 0

-25 -20 -15 -10 -5 0 5 10 15 20 25

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

Drain - source Voltage (V)

CN

T+

Si P

ho

tocu

rren

t (

A)

Vgs = -10 V

Vgs = -20 V

Vgs = -30 V

-25 -20 -15 -10 -5 0 5 10 15 20 25

-0,0015

-0,0010

-0,0005

0,0000

0,0005

0,0010

0,0015

0,0020

CN

T+

Si cu

rren

t (

A)


Vgs = -10 dark

Vgs = -20 dark

Vgs = -30 dark

Vgs = -10 light

Vgs = -20 light

Vgs = -30 light


S-D current through CNT+Si (ICNT + ISi)

-25 -20 -15 -10 -5 0 5 10 15 20 25

-1,5x10-3

-1,0x10-3

-5,0x10-4

0,0

5,0x10-4

1,0x10-3

1,5x10-3

2,0x10-3

Dra

in C

urr

ent I D

S (

A)


Vgs = -10 V dark

Vgs = -10 V dark

Vgs = -10 V dark

Vgs = -10 V light

Vgs = -10 V light

Vgs = -10 V light

-25 -20 -15 -10 -5 0 5 10 15 20 25

0,0

1,0x10-8

2,0x10-8

3,0x10-8

4,0x10-8

5,0x10-8

6,0x10-8

Pho

tocurr

en

t at ga

te I G

D.p

h (

A)


Vgs = -10 V

Vgs = -20 V

Vgs = -30 V

-25 -20 -15 -10 -5 0 5 10 15 20 25

10-9

10-8

10-7

10-6

10-5

Ph

oto

cu

rren

t a

t dra

in I

DS

,ph (

A)


Vgs = -10 V

Vgs = -20 V

Vgs = -30 V

-25 -20 -15 -10 -5 0 5 10 15 20 25

-2,5x10-6

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

Gate

curr

ent I G

S (

A)


Vgs = -10 V dark

Vgs = -20 V dark

Vgs = -30 V dark

Vgs = -10 V light

Vgs = -20 V light

Vgs = -30 V light


Comparison with vertical config

p-Silicon Si3N4

V

A

AuPt

-25 -20 -15 -10 -5 0 5 10 15 20 25

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4


CN

T+

Si P

ho

tocu

rren

t (

A)

Vgs = -10 V

Vgs = -20 V

Vgs = -30 V

-7,5 -5,0 -2,5 0,0 2,5 5,0 7,5

1E-10

1E-9

1E-8

1E-7

1E-6

Ph

oto

cu

rre

nt (A

)

Voltage (V)

Light on back

Conclusion:

From the shape of the obtained

Si + CNT photocurrent it seems that the Si photocurrent

component is dominating.

Too similar shape!


Photocurrent dominated by Si.

Very poor response of CNT, below the leakage current of a Si reverse biased device … but, if we increase the the

CNT thickness …


MCNT thick film (2-300 m)

-60 -40 -20 0 20 40 60 80 100 120 140 160

0,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1,10

Linear fit

R = 1.0-7.5E-4 T

Re

sis

tan

ce

(O

hm

)Temperature (°C)

T down

T up

T down

T down

T up

-60 -30 0 30 60 90 120 150

0,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1,10

Model:

Interrupted Metallic

Conduction

Chi 2 = 0.00002

R^2 = 0.99285

P1 -0.00057 ±0

P2 0.01572 ±18.74908

P3 0.49267 ±0

P4 701.43294 ±15.16466

P5 929.78472 ±20.93735

20 40 60 80 100 120

0,70

0,75

0,80

0,85

0,90

Model: Interrupted Metallic Conduction

Chi^2 = 0.00002

R^2 = 0.9903

P1 0.47708 ±0.00226

P2 112.56356 ±0.51601

P3 0.70542 ±0.00021

P4 0 ±0

P5 1 ±0

Linear fit

R = 0,65 + 0,0020 T

Resis

tan

ce (

Oh

m)

Temperature (°C)

T down

-0,010 -0,005 0,000 0,005 0,010

-0,010

-0,005

0,000

0,005

0,010

Cu

rre

nt (A

)

Voltage (V)

T = 140 °C

T = 65 °C

T = -40 °C

Study of R(T)

No GINT samples!


CNT film photoconductivity

50 60 70 80 90 100 110 120 130 140 150

0,755

0,760

0,765

0,770

0,775

0,780

0,785

0,790

Time (s)

Re

sis

tan

ce

(O

hm

)

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

Te

mp

era

ture

(°C)

0 100 200 300 400 500

0,755

0,760

0,765

0,770

0,775

0,780

0,785

0,790

Time (s)

Re

sis

tan

ce

(O

hm

)

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

Te

mp

era

ture

(°C)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

0,990

0,995

1,000

1,005

1,010

1,015

Time (Hour)

CN

T R

esis

tan

ce

(O

hm

)

22

23

24

25

26

27

28

Te

mp

era

ture

from

KT

-11

-6 (°C

)

No GINT samples!


Conclusion:

• CNTs show photoconductivity effects

• To compare photoconductivity of CNT and Si we have to compare sample with the same absorption thickness


Backup


Si substrate with Si3N4 layers

-10 -8 -6 -4 -2 0 2 4 6 8 10

-2,0x10-5

-1,0x10-5

0,0

1,0x10-5

2,0x10-5

Mea

su

red C

urr

en

t (A

)

Applied Voltage (V)

dark

100 W white lamp 30 cm

100 W white lamp 15 cm

R10V = 500 k

Silicon p

(no doping level known) Si3N4

VA

AuPt500 µm

100 nm

2e-5

-2 0 2

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

1,0x10-6

1,5x10-6

2,0x10-6

Me

asure

d C

urr

ent (A

)

Applied Voltage (V)

dark

100 W white lamp 15 cm 100 W white lamp 30 cm

• Not sure about Si3N4 thickness: ~ 100

nm

• We can assume ohmic contacts with

tunneling current through the oxide

barriers

• small sensitivity to light as expected

for ohmic contacts where photocurrent

is masked by high dark current

R1V = 850 k

2e-6


-10 -8 -6 -4 -2 0 2 4 6 8 10

-2,0x10-8

-1,5x10-8

-1,0x10-8

-5,0x10-9

0,0

5,0x10-9

1,0x10-8

1,5x10-8

2,0x10-8

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

Dark

Lab Light

100 W white lamp

Si substrate with Si3N4 layers and w/o CNTs

• Lower current due to a larger oxide barrier?

• Ohmic behaviour (tunneling current) with high contact resistance

• Small sensitivity to light (photocarriers blocked by the barriers?)

-2 0 2

-6,0x10-9

-4,0x10-9

-2,0x10-9

0,0

2,0x10-9

4,0x10-9

6,0x10-9

Mea

su

red

Cu

rren

t (A

)

Applied Voltage (V)

Dark

Lab Light

100 W white lamp

R1V = 2 G

2e-8

Silicon Si3N4

V

A

AuPt

6e-9

R10V = 625 M


Comb-to-comb structures with CNTs

Sample with CNTs.

IV curves with high sensitivity to light.

Lower contact resistance, i.e thinner Si3N4

barrier, allows higher photocarrier

collection

or CNT effect ?

-10 -8 -6 -4 -2 0 2 4 6 8 10

-3,5x10-5

-3,0x10-5

-2,5x10-5

-2,0x10-5

-1,5x10-5

-1,0x10-5

-5,0x10-6

0,0

5,0x10-6

1,0x10-5

1,5x10-5

2,0x10-5

2,5x10-5

3,0x10-5

3,5x10-5

Me

asu

red

Cu

rren

t (A

)

Applied Voltage (V)

ILabLight

IDark

ILamp25cm

ILight25cmOnOff

ILamp5cm

-4 -3 -2 -1 0 1 2 3 4

-5,0x10-6

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

1,0x10-6

2,0x10-6

3,0x10-6

4,0x10-6

5,0x10-6

Me

asure

d C

urr

ent (A

)

Applied Voltage (V)

ILabLight

IDark

ILamp25cm

ILight25cmOnOff

ILamp5cm

Silicon Si3N4

V

A

AuPt


Sample 1

3.5e-6

5e-6

Lamp 5/25 cm

Light lab

Dark

R10V = 1.3 M

R1V = 12 M


Comb-to-comb with and w/o CNTs (1)

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30

-8,0x10-4

-6,0x10-4

-4,0x10-4

-2,0x10-4

0,0

2,0x10-4

4,0x10-4

6,0x10-4

8,0x10-4

Mea

sure

d C

urr

ent (A

)

Applied Voltage (V)

IDarkCNT ILabLightCNT ILamp25cmCNT

IDarkNoCNT ILabLightNoCNT ILamp25cmNoCNT IDarkCNTfullyOut

VLabLightCNTfOut ILamp25cmCNTfOut

-20 -15 -10 -5 0 5 10 15 20

-6,0x10-5

-4,0x10-5

-2,0x10-5

0,0

2,0x10-5

4,0x10-5

6,0x10-5

Me

asure

d C

urr

en

t (A

)

Applied Voltage (V)

IDarkCNT

ILabLightCNT

ILamp25cmCNT

IDarkNoCNT

ILabLightNoCNT ILamp25cmNoCNT

IDarkCNTfullyOut

VLabLightCNTfOut

ILamp25cmCNTfOut

IV curves, measured with and without

CNTs, which were removed.

No significant difference:

Curves with CNT and without CNTs

very similar for all the lighting conditions

Removing CNT increases current.

Silicon Si3N4

V

A

AuPt


Sample 2

8e-4

6e-5

Dark•CNT•no CNT•No no CNT

Lab light•CNT•no CNT•No no CNT

Lamp


-20 -15 -10 -5 0 5 10 15 20

-6,0x10-5

-4,0x10-5

-2,0x10-5

0,0

2,0x10-5

4,0x10-5

6,0x10-5

Me

asu

red C

urr

ent (A

)

Applied Voltage (V)

IDarkCNT

ILabLightCNT ILamp25cmCNT

IDarkNoCNT ILabLightNoCNT ILamp25cmNoCNT

IDarkCNTfullyOut VLabLightCNTfOut

ILamp25cmCNTfOut

Silicon Si3N4

V

A

AuPt


Sample 2

Comb-to-comb with and w/o CNTs (2)

V

A

6e-5

Dark

AUnder light the reverse current

of the back-biased diode is increased and the diode lose its rectifying properties

Dark

Light


-12 -10 -8 -6 -4 -2 0 2 4

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

1,0x10-6

Cu

rre

nt (A

)

Voltage (V)

dark

lab light

white lamp at 25cm

white lamp at 10cm

white lamp at 10cm on-off

Schottky-Ohmic contacts: MIS tunnel diode

-28 -24 -20 -16 -12 -8 -4 0 4

-4,0x10-6

-3,5x10-6

-3,0x10-6

-2,5x10-6

-2,0x10-6

-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

1,0x10-6

Cu

rre

nt (A

)

Voltage (V)

dark

lab light

white lamp at 25cm

white lamp at 10cm

white lamp at 10cm on-off

Silicon Si3N4

V

A

AuPt

1e-6

1e-6• Curves obtained after electric stress -> broken ONE Si3N4 barrier?

• Rectifying effects and sensitivity to light for reverse bias.

• No tunneling through insulator barrier,

• likely hidden by interface states.

-

+

+

-


Light on Si with Schottky-Schottky cts

Lower photocurrent by illumination with a 40W white lamp:

(ILight – Idark) ~ 1 to 3 Idark

-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

-2,0x10-7

-1,5x10-7

-1,0x10-7

-5,0x10-8

0,0

5,0x10-8

1,0x10-7

1,5x10-7

2,0x10-7

2,5x10-7

3,0x10-7

Curr

ent (A

)

Voltage (V)

I1bc

I1bcLight

I2

I2Light

-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

I (L

igh

t -

Da

rk)

/ D

ark

Voltage (V)

20 M

10 M

-3 -2 -1 0 1 2 3

-2,0x10-7

-1,5x10-7

-1,0x10-7

-5,0x10-8

0,0

5,0x10-8

1,0x10-7

1,5x10-7

2,0x10-7

2,5x10-7

3,0x10-7

Curr

ent (A

)

Voltage (V)

dark

light on/off

Horizontal probe configuration Vertical probe configuration

-3 -2 -1 0 1 2 3

0,0

0,2

0,4

0,6

0,8

1,0

1,2

I (

Lig

ht-

Dark

) / D

ark

Voltage (V)

2e-72e-7

+

-


CNT on Si3N4-Si with light (3)

-20 -15 -10 -5 0 5

-1,2x10-4

-1,0x10-4

-8,0x10-5

-6,0x10-5

-4,0x10-5

-2,0x10-5

0,0

2,0x10-5

4,0x10-5

6,0x10-5

8,0x10-5

Me

asu

red

Cu

rre

nt

(A)

Applied Voltage (V)

dark

lab light

100w white lamp at 70 cm






-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2

-4,5x10-5

-4,0x10-5

-3,5x10-5

-3,0x10-5

-2,5x10-5

-2,0x10-5

-1,5x10-5

-1,0x10-5

-5,0x10-6

0,0

Mea

su

red

Cu

rre

nt (A

)

Applied Voltage (V)

dark

lab light






100w white lamp at 5 cm• Clear tunnelling through insulator barrier and negative resitance behaviour.

Silicon Si3N4

V

A

AuPt

lamp

d

d


MIS tunnel diode: IV curves vs light intensity

-20 -15 -10 -5 0 5

-4,0x10-4

-3,0x10-4

-2,0x10-4

-1,0x10-4

0,0

1,0x10-4

Without CNT

Me

asu

red

Cu

rre

nt (A

)

Applied Voltage (V)

dark

light

filter 79.8%

filter 62.5%

filter 50.2%

filter 25.2%

filter 15.1%

filter 6.7%

• 100 W withe lamp with intensity filters

• Reverse current monotonically increases with light intensity till a saturation

• Si3N4 barrier seen as negative

resistance in IV curves!

(see band diagram for explanation)

Dark

Light

Silicon Si3N4

V

A

AuPt

lamp

filter

4e-4

-10 -5 0 5

-5,0x10-6

-4,0x10-6

-3,0x10-6

-2,0x10-6

-1,0x10-6

0,0

Without CNT

Curr

ent (A

)

Voltage (V)

dark light



filter 15.1%

filter 6.7%

5e-6

-

+


Si3N4-Si with and w/o CNTs

-10 -8 -6 -4 -2 0 2 4 6 8 10

-2,0x10-5

-1,0x10-5

0,0

1,0x10-5

2,0x10-5

R = 550 kOhm

Y =-2,5E-8+1,8E-6 X

Mea

su

red

Cu

rre

nt (A

)

Applied Voltage (V)

light lab

white lamp 15 cm

white lamp 30 cm

Polynomial Fit of Data6_ILight2

-0,04 -0,02 0,00 0,02 0,04

-1,0x10-5

-5,0x10-6

0,0

5,0x10-6

1,0x10-5

Y =-8,3E-9+2,2E-4 X

Cu

rren

t (A

)

Voltage (V)

Light Lab

White lamp 14 cm

-6 -4 -2 0 2 4 6

-6,0x10-7

-4,0x10-7

-2,0x10-7

0,0

2,0x10-7

4,0x10-7

6,0x10-7

Y =-3,5E-9+6,6E-8 X

Y =3,4E-9+1,01E-7 X

Ph

oto

cu

rre

nt

(A)

Voltage (V)

light lamp 15 cm - lab

white lamp 30 cm - lab

-0,04 -0,02 0,00 0,02 0,04

-6,0x10-7

-4,0x10-7

-2,0x10-7

0,0

2,0x10-7

4,0x10-7

6,0x10-7

Y =5,0E-8+2,7E-6 X

Ph

oto

curr

en

t (A

)

Voltage (V)

Light lamp 15 cm - lab

no CNT

with CNT

GINT samples as metal -insulator -semiconductor (MIS) diodes · 14/01/2008 GINT coll. Meeting...

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Transcript of GINT samples as metal -insulator -semiconductor (MIS) diodes · 14/01/2008 GINT coll. Meeting...