金氧半光偵測器
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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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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

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

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

  • Summary

Outline


  • 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


  • Si-based CMOS optoelectronics

  • - low cost, high reliability, VLSI compatible

Introduction

Electrical Parts

Optical Parts


Introduction

  • Ge mole fraction 

     cut-off wavelength  absorption length 


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

Process flow of LPD oxynitride.

The proposed LPD-SiON mechanism.


  • The LPD-SiON has a lower

  • current than the LPD-SiO2.

Accumulation region

Inversion region


Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots

(a) Oxynitride

(b) Oxide


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.


SIMS profile of Oxynitride

O:N = 16:7 at the interface

Recess the top Ge dot


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:

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.


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

  • 5 ~ 20 layer self-assembled Ge quantum dots

  • prepared by UHVCVD under SK growth mode.


LPD vs. RTO (700 oC)

  • Devices with LPD oxide have higher efficiency.


Device Operation

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


Device Operation

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


Results and Discussion

  • Dark current of all 4 devices.

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


820 nm

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


1300 nm

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

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


1550 nm

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


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

  • 20 - period QDs, 50 nm spacers

  • High responsivity at 850 nm  0.6 A/W


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


  • 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)


  • 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 Fabrication

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

  • The confined holes have transitions under infrared exposures.


  • PL spectrum => QD barrier 0.3~0.4 eV

Discussion


  • Smaller dark current duo to lower Dit

Device Performance


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

Device Performance


  • 2~3 μm response up to 200 K

  • large response at short wavelength => interband transition

Device Performance


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

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.

Device Performance


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.


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.


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

Extra electron current from Pt gate

Photo generated

electron current in depletion region

No depletion region, low photo current


Hole blocking at low temperature

  • Hole blocking effect is more severer at low temperature.


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.


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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