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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. Introduction LPD Oxynitride Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots Ge/Si Quantum Dot MOS Photodetectors for Optical Communication

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金氧半光偵測器 Novel Metal-Insulator-Semiconductor Photodetector

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Novel metal insulator semiconductor photodetector

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


Outline

  • Introduction

  • LPD Oxynitride

  • Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots

  • Ge/Si Quantum Dot MOS Photodetectors for Optical Communication

  • MIS Ge/Si Quantum Dot Infrared Photodetectors (QDIP) (intraband transition)

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

  • Summary

Outline


Introduction

  • The electro-optical products may be one of the killer applications in the future Si market.

  • The worldwide revenue of the optical semiconductor 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

Introduction


Introduction1

  • Si-based CMOS optoelectronics

  • - low cost, high reliability, VLSI compatible

Introduction

Electrical Parts

Optical Parts


Novel metal insulator semiconductor photodetector

Introduction

  • Ge mole fraction 

     cut-off wavelength  absorption length 


Novel metal insulator semiconductor photodetector

NMOS detector response

  • Al gate

  • Zero bias

  • Cut-off wavelength = 1.18m

  • Ecutoff = 1.05 eV < Ebandgap

  • Phonon-assistant absorption (65 meV)


Lpd oxynitride

LPD Oxynitride

Process flow of LPD oxynitride.

The proposed LPD-SiON mechanism.


Novel metal insulator semiconductor photodetector

  • The LPD-SiON has a lower

  • current than the LPD-SiO2.

Accumulation region

Inversion region


Recessed oxynitride dots on self assembled ge quantum dots

Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots

(a) Oxynitride

(b) Oxide


Tensile strain

Tensile Strain :

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

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


Novel metal insulator semiconductor photodetector

SIMS profile of Oxynitride

O:N = 16:7 at the interface

Recess the top Ge dot


Dot height

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.


Afm morphologic

AFM Morphologic:

Quantum Dot

 AFM surface image and Cross-

section morphologyof LPD oxide

with 15 nm wetting layer thickness.

 AFM surface image and Cross-

section morphologyof LPD

oxynitride (1M NH4OH) with 15 nm

wetting layer thickness.


Novel metal insulator semiconductor photodetector

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.


Ge quantum dots

Ge Quantum Dots

  • 5 ~ 20 layer self-assembled Ge quantum dots

  • prepared by UHVCVD under SK growth mode.


Lpd vs rto 700 o c

LPD vs. RTO (700 oC)

  • Devices with LPD oxide have higher efficiency.


Device o peration

Device Operation

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


Device o peration1

Device Operation

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


Results and discussion

Results and Discussion

  • Dark current of all 4 devices.

  • The dark current of 5-layer QD device  0.06 mA/cm2


820 nm

820 nm

  • Efficiency of 5-layer Ge QD device  20%


1300 nm

1300 nm

  • Efficiency : 5-layer Ge QD (0.16 mA/W) >

  • multi-layer Si0.8Ge0.2 (0.04 mA/W)


1550 nm

1550 nm

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


Optimized qd structure

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


High efficiency at 850 nm

High Efficiency at 850 nm

  • 20 - period QDs, 50 nm spacers

  • High responsivity at 850 nm  0.6 A/W


Discussion

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


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

MOS Ge/Si QDIP( intraband transition)


Device fabrication

  • Grown by UHVCVD

Device Fabrication

  • 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


Device fabrication1

Device Fabrication

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

  • The confined holes have transitions under infrared exposures.


Discussion1

  • PL spectrum => QD barrier 0.3~0.4 eV

Discussion


Device performance

  • Smaller dark current duo to lower Dit

Device Performance


Device performance1

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

Device Performance


Device performance2

  • 2~3 μm response up to 200 K

  • large response at short wavelength => interband transition

Device Performance


Device performance3

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

Device Performance


Device performance4

  • 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.

Device Performance


A dual polarity operable mos photodetector with pt gate interband transition

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

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


Novel metal insulator semiconductor photodetector

Photo I-V

  • 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.


Novel metal insulator semiconductor photodetector

Pt & Al

  • 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.


Low temperature photo i v of ge quantum dot device

Low Temperature photo I-V of Ge quantum dot device

Extra electron current from Pt gate

Photo generated

electron current in depletion region

No depletion region, low photo current


Novel metal insulator semiconductor photodetector

Hole blocking at low temperature

  • Hole blocking effect is more severer at low temperature.


Conclusion

Conclusion

  • The tensile strain on the Si cap above self-assembled 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.


Novel metal insulator semiconductor photodetector

Conclusion

  • 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.


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