Si/SiGe Heterojunction Phototransistor

1
Si/SiGe Heterojunction Phototransistor

• Jin-Wei Shi1,, Z. Pei1,
• Y.-M. Hsu1, F. Yuan2, C.-S. Liang1, Y.-T. Tseng1,
  P.-S. Cheng1, C.-W. Liu1,2, S.-C. Lu1, M.-J.
  Tsai1

1 Electronics Research and Service Organization
(ERSO), Industrial Technology Research
Institute (ITRI), Hsinchu, 31040, TAIWAN 2
Department of Electrical Engineering, National
Taiwan University, Taipei 10617,
TAIWAN. Current address Department of
Electrical Engineering, National Central
University, Taoyuan, 320, TAIWAN.
2
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

3
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

4
Photo-transistor for Fiber Communication
Application

• Extremely High Responsivity
• Over 10A/W
• Much lower operation voltage than Avalanche
  Photodiode (APD)
• Much lower cost than APD and semiconductor
  optical amplifier (SOA)
• Circuit Level Integration
• HBTHPT (Hetero-junction Photo-transistor) OEIC1
  !!
• Lower fabrication cost than p-i-nHBT OEIC
• Analog fiber communication application of HPT2
• Clock recover O-E circuit, O-E Mixer
• Speed is critical issue for the application of
  HPT!!
• Optical fT for analog fiber application1
• Electrical f3dB for digital fiber application
• We will demonstrate a novel method to improve the
  gain-bandwidth product of HPT in this
  presentation !!

1. H. Wang, et al., IEEE Trans. Microwave Theory
Tech., vol. 34, Dec. 1986. 2. H. Kamitsuna, et
al., IEEE Trans. Microwave Theory Tech., vol. 49,
Oct. 2001.
5
Why Si/SiGe Based HPT ?

• Low Responsivity of Si based p-i-n Photodetectors
  (PDs)1
• High operation gain of photo-transistor can
  overcome this drawback
• Much Lower Operation Voltage than APD
• Without voltage or temperature control circuit
• Low cost !!
• High gain/speed2, yield and reliability of SiGe
  HBT
• In plane structure of Si/SiGe based HBT has
  higher yield and reliability than etch-mesa
  structure of III-V based HBT3
• Si/SiGe based TIAHPT
• Almost without modification of standard TIA
  fabrication process
• Low cost!!
• Analog nonlinear application of SiGe based HPT
• Clock recover O-E circuit, O-E Mixer

1. B. Yang, et al., IEEE Photonic Technology
Letters, vol. 15, May 2003. 2. B. Jagannathan, et
al., IEEE Electron Device Letters, vol. 23, May,
2002. 3. Z. Ma, et al., IEEE Trans. Microwave
Theory Tech., vol. 50, April, 2002.
6
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

7
Cross-Sectional and Top Views of Fabricated
Si/SiGe HPT
MQW at B-C Junction !!
The same as SiGe HBT !!
Two types of HPT are fabricated (with/without
MQW) The photo-absorption process is enhanced by
incorporating Si/SiGe MQW at B-C junction!!
Fiber communication long wavelengths
(1.31.55mm) photo-absorption can be achieved by
using SiGe alloy1
1. H. Lafontaine, et al., Journal of applied
physics vol. 86, Aug. 1999.
8
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

9
Gummel Plot of Si/SiGe HPT with/without MQW
QW structure at B-C junction doesn'tt affect the
electrical gain significantly !!
10
fT fmax of Si/SiGe HPT with/without MQW
ft is the key parameter at the application of
analog circuit QW structure has higher fmax but
lower ft than ordinary HBT due to the extra
thickness of MQW at collector !! High conversion
gain of SiGe based O/E mixer1 can be expected due
to high ft and high b
1. H. Kamitsuna, et al., IEEE Trans. Microwave
Theory Tech., vol. 49, Oct. 2001.
11
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

12
Photo-DC Measurement Results- with/without QW
structure
Excitation Wavelength 850nm
QW structure at B-C junction enhance the
responsivity significantly!! The responsivity is
much higher than the reported values (0.1A/W) of
Si based PDs at 850nm wavelength1 Higher
responsivity can be expected by improving
coupling optics!!
1. B. Yang, et al., IEEE Photonic Technology
Letters, vol. 15, May 2003.
13
Photo-DC Measurement Results- Nonlinear
Behaviors at Near Breakdown Region
Responsivity enhancement1 Photo-absorption
bleach2 at near breakdown voltage !!
Optoelectronic Mixer1,2
1. E. Suematsu and N. Imai, IEEE Trans. Microwave
Theory Tech., vol. 44, pp.133-143, 1996.
2. M. Tsuchiya, and T. Hosida, IEEE Trans.
Microwave Theory Tech., vol. 47, 1999.
14
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

15
Speed Performance of HPT

• Speed limits the application of HPT in the field
  of digital fiber communication
• Poorer speed performance than p-i-n or APD
• What are the prior arts to improve speed
  performance of HPT ?
• Base termination technique1,2,3
• Turn on the B-E junction to remove the excess
  hole at base
• Significant speed enhancement 1,2
• Huge dc power consumption (dark current)!!
• At the expense of optical gain1,2!!
• What is the optimum solution?

1. M. Y. Frankel, et. al., IEEE Journal of
Quantum Electronics, vol. 31, Feb. 1995. 2. T. F.
Carruthers, et. al., Appl. Phys. Lett., vol. 63,
no. 14, Oct. 1993. 3. S. Chandrasekhar, et. al.,
IEEE Electron Device Letters, vol. 12, Oct. 1991.
16
Our Novel Solution- Side-Wall Terminal Technique

• General solutions for speed enhancement in III-V
  and Si based HPTs
• Especially suitable to SiGe based HPTs with
  planar structure
• Significant speed improvement with less gain
  sacrifice and increase in dark current
• Open a new field for HPTs OEIC (Opto-Electronic
  Integrated Circuit)

17
Cross-Section of Novel Side-Wall Contact SiGe
Based HPTs without MQW
Photo-generated hole can be removed by side-wall
terminal (lateral p-n junction) instead B-E
junction Similar to standard substrate contact
process of SiGe based HBT!!
18
Cross-Section of Novel Side-Wall Contact MQW/MQD
SiGe Based HPTs
Hole trapping problem due to thick MQW/MQD
barrier can be eliminated by P-type doped at
well region and side-wall terminal
19
Using Substrate Contact to Primarily Demonstrate
this Idea
Standard SiGe HPT substrate contact process!!
Substrate contact is grounded with emitter
contact Large parasitic resistance !! Better
speed performance can be expected!!
20
Superior Performance of HPT without MQW by using
Side-Wall Terminal Technique
Use Substrate contact to demonstrate this idea!!
Side-wall terminal floating Trace A Base
terminal floating Trace B Base terminal
grounding
Base terminal floating Trace A Side-wall
terminal floating Trace B Side-wall terminal
grounding
FWHM enhancement 2.5 ns ? 0.95 ns Photocurrent
reduction 15 mA ? 0.1 mA
FWHM enhancement 2.5 ns ? 0.85 ns Photocurrent
reduction 15 mA ? 8.7mA
Side-Wall contact terminal technique can achieve
much higher gain-bandwidth product as compared
with Base terminal technique!!
21
Superior Performance of MQW HPT by using
Side-Wall Terminal Technique
Use Substrate contact to demonstrate this idea!!
Base terminal floating Trace A Side-wall
terminal floating Trace B Side-wall terminal
grounding
Side-wall terminal floating Trace A Base
terminal floating Trace B Base terminal
grounding
FWHM enhancement 7.7 ns ? 1 ns Photocurrent
reduction 90 mA ? 45 mA
FWHM enhancement similar to 7.7 ns Photocurrent
reduction 90 mA ? 0.11 mA
Side-Wall contact terminal is more useful than
base terminal at quantized structure !!
22
Advantages of Side-Wall Terminal

• Side-wall terminal can remove the storage hole at
  base region without huge dark current
• With less sacrifice for operated gain
• Side-wall terminal can solve the problem of hole
  trapping at MQW structure
• SiGe based QW structure play important role for
  long wavelength detection
• The problem of hole trapping limits the speed
  performance of SiGe based PDs1
• Lateral conduction can solve this problem
• Open a new field for HPT based OEIC!!
• Use substrate terminal to distort input RF signal
• Novel optoelectronic mixer

1. C. Li et al., IEEE Photon. Technol. Lett.,
vol. 12, pp. 1373-1375, Oct. 2000.
23
High Speed Performances by Using Side-Wall
Termination Technique under low power
illumination
HPT without MQW
HPT with MQW
Speed performance of PDs can be improved
significantly under low power excitation1
MQW structure has much higher optical gain than
control SiGe HPT, but poorer speed performance !!
1. Y.-L. Huang and C.-K. Sun, Journal of
Lightwave Technology, vol. 18, 2000.
24
Bandwidth-Responsivity Products of Different
Types of HPT
MWQ structure has much higher bandwidth-responsivi
ty product than ordinary HPT !!
High speed (3GHz) with reasonable responsivity
(gt0.4A/W) performances of standard HPT ensure its
application of 850nm short-reach data comm. !!
High bandwidth-efficiency product and high ft
performance of MQW HPT imply its applications in
low-cost clock recovery circuits or
optoelectronic mixer !!
25
Outline

• Motivation
• Structures of Si/SiGe Heterojunction
  Phototransistor
• Electrical measurement results
• Optical dc measurement results
• Side-Wall Terminal Technique Optical Transient
  Measurement Results at 850nm
• Conclusion

26
Conclusion

• Two types of SiGe based HPT are demonstrated
• MQW structure at B-C junction can improve
  responsivity significantly
• Side-wall terminal technique can improve the
  speed performance of two HPT structures
  significantly with less gain reduction and
  eliminate huge dc power consumption
• Ordinary HPT structure has the application of
  850nm short reach 2.5G/bits data communication
• MQW HPT structure has the application of 850nm
  optoelectronic mixer