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MWP 2003
Jin-Wei Shi
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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
•
HBT+HPT (Hetero-junction Photo-transistor) OEIC1 !!
•
Lower fabrication cost than p-i-n+HBT 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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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 TIA+HPT
– 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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
Cross-Sectional and Top Views of
Fabricated Si/SiGe HPT
MQW at B-C Junction !!
MWP 2003
Jin-Wei Shi
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 (1.3~1.55mm) photo-absorption can be achieved
by using SiGe alloy1
1. H. Lafontaine, et al., Journal of applied physics vol. 86, Aug. 1999.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
Gummel Plot of Si/SiGe HPT with/without
MQW
0.1
Ib MQW
Ib HBT
Ic,Ib(A)
1E-3
1E-5
=~200
1E-7
1E-9
1E-11
0.4
0.6
0.8
Vbe(V)
1.0
QW structure at B-C junction doesn't’t affect the electrical gain
significantly !!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
fT fmax of Si/SiGe HPT with/without MQW
fT,fmax (GHz)
50
40
MQW ft
MQW fmax
HBT ft
HBT fmax
Peak ft
Peak fmax
30
20
10
10k
2
Jc(A/cm )
100k
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 
1. H. Kamitsuna, et al., IEEE Trans. Microwave
Theory Tech., vol. 49, Oct. 2001.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
Photo-DC Measurement Resultswith/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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
Photo-DC Measurement ResultsNonlinear Behaviors at Near Breakdown Region
Trace A~E:
Optical Power 0.2mW~0.4mW
(Step:0.05mW)
1E-4
E
D
C
B
A
Breakdown (~2.5V)!!
Responivity Enhancement !!
1E-5
0
1
VCE(V)
2
Photo-current ( mA)
Photocurrent (A)
180 Photon-absorption Bleach
D
150
A:VCE=0.5V
B:VCE=1V
C:VCE=2V
D:VCE=2.5V
120
90
60
A,B,C
30
0.20
0.25
0.30
0.35
0.40
Optical Power (mW)
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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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.
Industrial Technology Research Institute
Electronics Research & Service Organization
Our Novel Solution-
MWP 2003
Jin-Wei Shi
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 (OptoElectronic Integrated Circuit)
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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!!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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!!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
Superior Performance of HPT without MQW
by using Side-Wall Terminal Technique
Use Substrate contact to demonstrate this idea!!
Amplitude (a.u.)
1.0
0.8
A
B
0.6
VCE = 1 V
Avg. Optical
Power: 5mW
0.4
0.2
1.0
VCE = 1 V
Avg. Optical
Power: 5mW
0.8
0.6
A
0.4
B
0.2
0.0
0.0
-0.2
Side-wall terminal floating :
Trace A : Base terminal floating
Trace B : Base terminal grounding
Amlpitude (a.u.)
Base terminal floating :
Trace A : Side-wall terminal floating
Trace B : Side-wall terminal grounding
0
100
200 300
Time (ns)
400
500
-0.2
0
100
200 300 400
Time (ns)
500
FWHM enhancement : 2.5 ns  0.85 ns
FWHM enhancement : 2.5 ns  0.95 ns
Photocurrent reduction : 15 mA  8.7mA
Photocurrent reduction : 15 mA  0.1 mA
*Side-Wall contact terminal technique can achieve much
higher gain-bandwidth product as compared with Base
terminal technique!!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
1.2
VCE = 1 V
Avg. Optical
Power: 5mW
Amplitude (a.u.)
1.0
0.8
B
0.6
0.4
A
0.2
0.0
VCE = 1 V
Avg. Optical
Power: 5mW
1.0
Amplitude (a.u.)
1.2
-0.2
Side-wall terminal floating :
Trace A : Base terminal floating
Trace B : Base terminal grounding
0.8
0.6
0.4
0.2
0.0
-0.2
0
100 200 300 400 500 600
Time (ns)
0
100
200
300 400
Time (ns)
500
600
FWHM enhancement : 7.7 ns  1 ns
FWHM enhancement : similar to 7.7 ns
Photocurrent reduction : 90 mA  45 mA
Photocurrent reduction : 90 mA  0.11 mA
*Side-Wall contact terminal is more useful than base
terminal at quantized structure !!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
High Speed Performances by Using Side-Wall Termination
Technique under low power illumination
HPT without MQW
HPT with MQW
1.2
0.8
Avg. Optical
Power: 90nW
0.6
0.4
0.2
0.0
-0.2
0
400
800
Time (ps)
1200
1.0
Amplitiude (a.u.)
Amplitiude (a.u.)
1.0
FWHM = 93 ps
Bandwidth=~3GHz
Instrument Limited
Bandwidth
0.8
Avg. Optical
Power: 90nW
FWHM = 136 ps
Bandwidth=0.5GHz
0.6
0.4
0.2
0.0
-0.2
0
1000
2000
3000
Time (ps)
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.
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
Bandwidth-Responsivity Products of
Different Types of HPT
MWQ structure has much higher bandwidth-responsivity
product than ordinary HPT !!
Bnadwidth-Responsivity
Product (GHz-A/W)
90
75
60
45
HPT without MWQ (3GHz)
HPT with MQW (0.5GHz)
30
15
0
0.8
1.2
1.6
VCE (V)
2.0
2.4
High speed (~3GHz) with reasonable responsivity (>0.4A/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 !!
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization
MWP 2003
Jin-Wei Shi
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
Industrial Technology Research Institute
Electronics Research & Service Organization