1

金氧半光偵測器

Novel Metal-Insulator-Semiconductor Photodetector

•指導教授：劉致為 博士•學生：郭平昇•台灣大學電子工程學研究所

2

Outline

• Introduction• LPD Oxynitride• Recessed Oxynitride Dots on Self-assembled Ge

Quantum Dots• Ge/Si Quantum Dot MOS Photodetectors for Opti

cal Communication• MIS Ge/Si Quantum Dot Infrared Photodetectors

(QDIP) (intraband transition)• A Dual-polarity Operable MOS Photodetector with

Pt Gate (interband transition)• Summary

3

Introduction• The electro-optical products may be one of the

killer applications in the future Si market.• The worldwide revenue of the optical semicon

ductor is ~5 % (~7 B) of the total semiconductor revenue (~140 B) 2002.

(Note RF: 4.7 B, MEMS : 4.6 B)

• The ITRS has predicted that the incorporation of optoelectronic components into CMOS-compatible process is needed to achieve System-on-a-Chip.

• CMOS optoelectronics: OE Devices fabricated by CMOS available technology

4

Introduction

• Si-based CMOS optoelectronics

- low cost, high reliability, VLSI compatible

Electrical PartsOptical Parts

5

0.0 0.2 0.4 0.6 0.8 1.00.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

strained SiGe

relaxed SiGe

Ge mole fraction

E n

e r

g y

( e

V )

2.42.22

1.8

1.6

1.4

1.2

1

w a v e l e n

g t h

( m )

0.0 0.2 0.4 0.6 0.8 1.010-2

10-1

100

101

102

103

strained SiGe

1550 nm

1300 nm

820 nm

Abs

orpt

ion

Len

gth

( m

)

Ge mole fraction

Introduction

• Ge mole fraction cut-off wavelength absorption length

6

0.90 0.95 1.00 1.05 1.10 1.15 1.20

Inte

nsity

(arb

itrar

y un

it)

Wavelength (m)

1.18m

NMOS detector response

• Al gate• Zero bias• Cut-off wavelength

= 1.18m• Ecutoff = 1.05 eV <

Ebandgap

• Phonon-assistant absorption (65 meV)

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LPD Oxynitride

H2SiF6 3.09 mol/l

H2SiF6 2 mol/l

SiO2 Saturated H2SiF6

SiO2:xH2O

LPD SiON Coated Si

Heat Treatment

NH4OH

P-Si Substrate

O O O

Si Si SiO Si OO

O O

Si SiO Si SiO Si O

O O

O

N

H H

N

F

OH

N F

N

N

F

N

H

N

H

O

Si

O

Si

+ H2O

O

H H

LPD SiON

dehydration

Si SiO

O

O

O

O

H H

SiOx SiOx SiOx SiOx SiOxNative oxide

P-Si substrate

N

H H

O H

F

N

Process flow of LPD oxynitride. The proposed LPD-SiON mechanism.

8

-3 -2 -1 0 1 2 31E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

substrate

LPD oxide

Al

Cur

rent

(A)

Voltage (V)

SiO2 1nm SiON 0.3M NH4OH 1nm SiON 0.5M NH4OH 1nm

Al

traps

P - Si

3.1 e.V

4.7 e.V

P - Si

Al

traps

dominant

Accumulation region Inversion region

• The LPD-SiON has a lower current than the LPD-SiO2.

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Recessed Oxynitride Dots on Self-assembled G

e Quantum Dots

oxide dot

Ge dot

20 nm

(a) Oxynitride (b) Oxide

10

Tensile Strain :

GeSi spacer

GeSi spacer

GeSi cap

SiO2/SiON

p-type Si substrate

Si buffer layer ~ 50nm

~100nm ~2nm

~6nm

•The tensile strain can enhance the oxynitride deposition rate on the strained Si on SiGe 20% buffers.

•The Si cap area above the Ge dots has a tensile strain, and the Si cap area on Ge wetting layers is strain free.

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O:N = 16:7 at the interface

SIMS profile of Oxynitride

Recess the top Ge dot

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Dot Height

• The LPD-SiON has a higher deposition rate as compared to the LPD-

SiO2, and the deposition rate increases as ammonia concentration

increases.

• Under the same wetting layer thickness, the LPD-SiON dots still yield

a higher dot height.

13

AFM Morphologic :

Quantum Dot

AFM surface image and Cross- section morphology of LPD oxynitride (1M NH4OH) with 15 nm wetting layer thickness.

AFM surface image and Cross- section morphology of LPD oxide with 15 nm wetting layer thickness.

14

Quantum Ring

Depostion time : (a) 12 min (b) 20 min.

• The tensile strain area can have preferential oxide deposition. • The LPD-SiO2 deposited on quantum ring sample acts just like the stalactite.

15

Ge Quantum Dots

• 5 ~ 20 layer self-assembled Ge quantum dots prepared by UHVCVD under SK growth mode.

p-Si substrate

Si buffer layer 50 nm

Active region (x layers)

Wetting layer2 nm

Si spacer50 nm

Ge DotSi cap 3 nm

16

LPD vs. RTO (700 oC)

• Devices with LPD oxide have higher efficiency.

1300 nm 1550 nm

RTO oxideLPD oxide

Effic

ien

cy (

a.u

.)

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Device Operation

• I-V curves at 820 nm (device area = 3x10-4 cm2)

-2 -1 0 1 2 3

5-layer QD device10-12

10-9

10-6

10-3

1.5 mW 1.0 mW 0.5 mW dark current

C

u r

r e

n t

( A

)

Voltage ( V )

18

Al

traps

hv

quantum dot

wetting layer

dark currentphotocurrent

Device Operation

• Carriers can tunnel through oxide via the assistance of multiple traps.

19

Results and Discussion

0.0 0.5 1.0 1.5 2.0

10-11

10-8

10-5

10-2

D

ark

Cu

rren

t (A

)

| Vg | ( V )

Multi-layer Si0.8

Ge0.2

Ge 5-layer Quantum dot Si

• Dark current of all 4 devices.• The dark current of 5-layer QD device 0.06 mA/cm2

20

820 nm

• Efficiency of 5-layer Ge QD device 20%

0.4 0.6 0.8 1.0 1.2 1.4 1.6

100

101

102

Vg = 2 V

Ge 5-layer Quantum dot S i Multi-layer Si

0.8Ge

0.2

Power ( m W )

Res

po

nsi

vity

( m

A/W

)

10-3

10-2

10-1

820 nm Extern

al Qu

antu

m E

fficiency

21

1300 nm

• Efficiency : 5-layer Ge QD (0.16 mA/W) > multi-layer Si0.8Ge0.2 (0.04 mA/W)

0.4 0.6 0.8 1.0 1.2 1.4 1.6

10-2

100

1021300 nm

Ge 5-layer Quantum dot Multi-layer Si

0.8Ge

0.2

Vg = 2 V

Res

po

nsi

vity

( m

A/W

)

Power ( mW )

10-7

10-3

10-5

10-1

Extern

al Qu

antu

m E

fficiency

22

1550 nm

• Only Ge and 5-layer Ge QD detectors have response.

0.4 0.6 0.8 1.0 1.2 1.4 1.6

10-3

10-1

101

1031550 nm

Ge 5-layer Quantum dot

Vg = 2 V

Power ( mW )

Res

pons

ivity

( m

A/W

)

10-3

10-5

10-7

10-1

External Q

uantum E

fficiency

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Optimized QD Structure

• Optimize number of periods and Si spacer layer thickness.

• Number of periods 5, 10, 20 periods

• Si spacer thickness 20 nm, 50 nm

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High Efficiency at 850 nm

• 20 - period QDs, 50 nm spacers• High responsivity at 850 nm 0.6 A/W

-2 -1 0 1 2 310-8

1x10-5

10-2

101

850 nm

Cu

rren

t D

ensi

ty (

A/c

m2 )

Gate Voltage ( V )

1 mW 0.5 mW 0.25 mW Dark

0.2 0.4 0.6 0.8 1.010-2

100

102

Res

po

nsi

vity

( m

A /

W )

Light Intensity ( mW )

@ 3 V 850 nm 1310 nm 1550 nm

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Discussion

• Quantum dot periods Responsivity • Si spacer thickness

dark current ↓ ( x 10-3 )

• For 20-period QDs, 50 nm spacers

- High responsivity 0.6 A/W at 850 nm

- Low dark current 0.3 mA/cm2

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MOS Ge/Si QDIP ( intraband transition) • Quantum dot infrared photodetector (QDIP)

=> low dark current, high operation temperature and normal incident detection

• Applications => military, medical, astronomical and many others.

• The MOS structure with tunneling insulator can make the Ge/Si QDIP

=> small dark current

compatible with Si ULSI process

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Device Fabrication

Si substrate

Si buffer layer 50 nm

Ge wetting layer (quantum well)

Ge quantum dot

Si spacer layer 50 nm

Si cap layer 3 nm

oxideAl

20 nm

• Grown by UHVCVD• The base width and height of the Ge dots are ~100 nm and

6~7 nm, respectively. The Ge dot density is ~1010 cm-2

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• Dark current is limited by minority generation rate (from Dit and bulk traps).

• The confined holes have transitions under infrared exposures.

Device Fabrication

Al

Infrared

Darkcurrent

SiO2

E1

E2

Wetting layerQD

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Discussion

• PL spectrum => QD barrier 0.3~0.4 eV

0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15

Wetting layersignals

barrier ~ 0.3 eV Si

SiTO

Ge QD signals

20 K

Inte

nsit

y (

A. U

.)

Photon energy ( eV )

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Device Performance

0.0 0.5 1.0 1.5 2.0 2.5 3.0

77 K

200 K

300 K

10-9

10-6

10-3

100

C

urr

en

t D

en

sit

y (

A / c

m2 )

Gate Voltage ( V )

Oxide Oxynitride

• Smaller dark current duo to lower Dit

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2 3 4 5 6 7 8 9 10

0.00

0.01

0.02

0.03

0.04

0.05

0.06

QD

QW

140 K

120 K

100 K

80 K

60 K

40 K

20 K

R

esp

on

siv

ity

( m

A / W

)

Wavelength ( m )

OxynitrideV

g = 5 V

• The operating temperature reaches 140 K for 3~10μm detection. Device Performance

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Device Performance

• 2~3 μm response up to 200 K

• large response at short wavelength => interband transition

1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.00.000

0.002

0.004

0.006

0.008

0.010

200 K

160 K

120 K

100 K

60 K

20 K

OxynitrideV

g = 5 V

Wavelength ( m )

Resp

on

siv

ity

( m

A / W

)

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Device Performance

20 40 60 80 100 120 140 160 180 200107

108

109

1010

1011

Temperature ( K )

D* (

cm

Hz1

/2 / W

)

6.8 m

2.7 m

Oxynitride V

g = 1 V

Vg = 5 V

• Peak Detectivity @ 100 K ~ 1010 cmHz0.5/W

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Device Performance

• The normalized detectivity D* is defined as:

• A is the detector area, Δf is the equivalent bandwidth of the electronic system, and NEP = in/R is the noise equivalent power. The in is current noise and R is the responsivity.

• The current noise is limited by the dark current and can be approximated as the shot noise (2eIdΔf)1/2, where Id is the measured dark current.

Ri

fA

NEP

fAD

n /*

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A Dual-polarity Operable MOS Photodetector with Pt Gate (interband transition)

-10 -8 -6 -4 -2 0 2 410-10

10-8

10-6

1x10-4

10-2 Pt gate

Die Area 3E-4 cm2

p-Si substrate

Si buffer layer 50 nm

Ge wetting layer

Ge quantum dot

Si spacer layer 60 nm

Si cap layer 100 nm

Ge quantum dot device Si device

Gat

e C

urr

ent

(A)

Gate Voltage ( V )

Pt

3.1 eV

4.5 eV

4.3 eV

4.6 eV

(a)

dominate

3.1 eV

4.6 eV

Pt

4.3 eV

4.5 eV

(b)

•The quantum dot device has lower current as compared to the Si device both in accumulation and inversion region due to hole blocking effect.

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-10 -8 -6 -4 -2 0 2 410-11

1x10-8

1x10-5

1x10-2

Pt gate has photo-response

Die Area 3E-4 cm2

photo current

dark current

850 nmIntensity = 1 mW

Gat

e C

urr

ent

( A

)

Gate Voltage ( V )

Al Device Pt Device

• The Q.D device with Pt gate has photo-response under accumulation region due to Pt has larger workfunction 5.3 e.V ( high electron barrier = 4.3 eV ). Al has lower barrier : 3.1 eV.

Photo I-V

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-10 -8 -6 -4 -2 0 2 41E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

Pt P-Si

Pt quantum dot

Al P-Si

Al quantum dot

LPD-SiO2 25A

Cu

rren

t (A

)

Voltage (V)

Al P-Si Al QD100-60 Pt P-Si Pt QD100-60

•For Al gate device, quantum dot has higher inversion current than Si due to Ge dot has a smaller bandgap.

•There is a inverse trend for Pt gate device due to hole blocking effect.

Pt & Al

Pt

3.1 eV

4.5 eV

4.3 eV

5.7 eV

3.1 eV

Al

4.6 eV

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Low Temperature photo I-V of Ge quantum dot device

Pt

3.1 eV

4.5 eV

4.3 eV

4.6 eV

(a)

dominate

3.1 eV

4.6 eV

Pt

4.3 eV

4.5 eV

(b)

-14 -12 -10 -8 -6 -4 -2 0 2 41E-13

1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

100 K

photo current

dark current

Cu

rrre

nt

(A)

Voltage (V)

Photo generated

electron current in depletion regionNo depletion

region, low photo current

Extra electron current from Pt gate

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100 150 200 250 3001E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

Die area 1.5E-3 cm2

Pt

+ 3V

P-Si quantum dot

Dar

k C

urr

ent

(A)

Temperature (K)

Hole blocking at low temperature

Pt

3.1 eV

4.5 eV

4.3 eV

4.6 eV

dominate

• Hole blocking effect is more severer at low temperature.

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Conclusion• The tensile strain on the Si cap above self-assemble

d quantum dots can probably enhance the etching rate of Si and have a preferential oxynitride deposition on the Ge dots during LPD process.

• Due to the N atoms passivation of the interface states, the device with oxynitride yields a lower dark current as compared to oxide device.

• The MOS Ge/Si QDIPs for 2 ~ 10 μm using hole inter-valance subband transitions are successfully demonstrated. The maximum operating temperature is 140 K for 3 ~10 μm and is up to 200 K for 2 ~ 3 μm detection with LPD oxynitride.

41

• The MOS Ge quantum dot devices can have high responsivity (0.6 A/W at 850 nm) and low dark current. • Oxide is grown by LPD and Ge quantum

dot structures are prepared by UHVCVD. • MOS Ge quantum dot devices Si spacer thickness dark current↓( x10-3 )• The NMOS Ge quantum dot photodetector with Pt gate can be operated in both inversion and accumulation regions. The valence bandoffset in Si/Ge heterojunction can confined the hole and form a energy barrier to block the hole current.

Conclusion