Si/SiGe Heterojunction Phototransistor

Industrial Technology Research InstituteElectronics Research & Service Organization

MWP 2003Jin-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.


MWP 2003Jin-Wei Shi

• Motivation• Structures of Si/SiGe Heterojunction Phototra

nsistor• Electrical measurement results • Optical dc measurement results • Side-Wall Terminal Technique & Optical Tran

sient Measurement Results at 850nm • Conclusion

Outline


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

• 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 prod

uct of HPT in this presentation !!

Photo-transistor for Fiber Communication Application

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.


MWP 2003Jin-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 t

han 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.


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

Cross-Sectional and Top Views of Fabricated Si/SiGe HPT

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 (1.3~1.55m) photo-absorption can be achieved by using SiGe alloy1

MQW at B-C Junction !! The same as SiGe HBT !!

1. H. Lafontaine, et al., Journal of applied physics vol. 86, Aug. 1999.


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

QW structure at B-C junction doesn't’t affect the electrical gain significantly !!

Gummel Plot of Si/SiGe HPT with/without MQW

0.4 0.6 0.8 1.01E-11

1E-9

1E-7

1E-5

1E-3

0.1

=~200

I c,Ib(

A)

Vbe

(V)

Ib MQW

Ib HBT


MWP 2003Jin-Wei Shi

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

1. H. Kamitsuna, et al., IEEE Trans. Microwave Theory Tech., vol. 49, Oct. 2001.

10k 100k

10

20

30

40

50

Peak fmax

Peak ft

f T,f max

(GH

z)

Jc(A/cm2)

MQW ft MQW fmax HBT ft HBT fmax


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

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!!

Excitation Wavelength: 850nm

1. B. Yang, et al., IEEE Photonic Technology Letters, vol. 15, May 2003.

Photo-DC Measurement Results-with/without QW structure


MWP 2003Jin-Wei Shi

0 1 21E-5

1E-4

Breakdown (~2.5V)!!Responivity Enhancement !!

EDCBA

Trace A~E: Optical Power 0.2mW~0.4mW (Step:0.05mW)

Pho

tocu

rren

t (A

)

VCE

(V)

0.20 0.25 0.30 0.35 0.4030

60

90

120

150

180 Photon-absorption BleachD

A,B,C

A:VCE

=0.5VB:V

CE=1V

C:VCE

=2VD:V

CE=2.5V

Pho

to-c

urre

nt (

A)

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, 199

9.

Photo-DC Measurement Results- Nonlinear Behaviors at Near Breakdown Region


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

• 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?

Speed Performance of HPT

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.


MWP 2003Jin-Wei Shi

• 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)

Our Novel Solution-Side-Wall Terminal Technique


MWP 2003Jin-Wei Shi

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!!

Cross-Section of Novel Side-Wall Contact SiGe Based HPTs without MQW


MWP 2003Jin-Wei Shi

“Hole trapping problem” due to thick MQW/MQD barrier can be eliminated by P-type doped at well region and side-wall terminal

Cross-Section of Novel Side-Wall Contact MQW/MQD SiGe Based HPTs


MWP 2003Jin-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!!


MWP 2003Jin-Wei Shi

FWHM enhancement : 2.5 ns 0.85 nsPhotocurrent reduction : 15 A 8.7A

Superior Performance of HPT without MQW by using Side-Wall Terminal Technique

FWHM enhancement : 2.5 ns 0.95 nsPhotocurrent reduction : 15 A 0.1 A

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

0 100 200 300 400 500-0.2

0.0

0.2

0.4

0.6

0.8

1.0 VCE = 1 VAvg. Optical Power: 5W

BA

Am

plitu

de (a

.u.)

Time (ns)0 100 200 300 400 500

-0.2

0.0

0.2

0.4

0.6

0.8

1.0 VCE

= 1 VAvg. Optical Power: 5W

B

A

Am

lpitu

de (a

.u.)

Time (ns)

*Side-Wall contact terminal technique can achieve much higher gain-bandwidth product as compared with Base

terminal technique!!

Use Substrate contact to demonstrate this idea!!


MWP 2003Jin-Wei Shi

*Side-Wall contact terminal is more useful than base terminal at quantized structure !!

0 100 200 300 400 500 600-0.20.00.20.40.60.81.01.2 V

CE = 1 V

Avg. Optical Power: 5W

Am

plitu

de (a

.u.)

Time (ns)0 100 200 300 400 500 600

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2 VCE

= 1 VAvg. Optical Power: 5W

B

A

Am

plitu

de (a

.u.)

Time (ns)

FWHM enhancement : 7.7 ns 1 nsPhotocurrent reduction : 90 A 45 A

FWHM enhancement : similar to 7.7 nsPhotocurrent reduction : 90 A 0.11 A

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

Superior Performance of MQW HPT by using Side-Wall Terminal Technique

Use Substrate contact to demonstrate this idea!!


MWP 2003Jin-Wei Shi

• 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 trapp

ing at MQW structure• SiGe based QW structure play important role for long wavelength d

etection• 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.

Advantages of Side-Wall Terminal


MWP 2003Jin-Wei Shi

0 400 800 1200-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Avg. Optical Power: 90nW

FWHM = 93 ps Bandwidth=~3GHz Instrument Limited Bandwidth

Am

pliti

ude

(a.u

.)

Time (ps)

High Speed Performances by Using Side-Wall Termination Technique under low power illumination

0 1000 2000 3000-0.2

0.0

0.2

0.4

0.6

0.8

1.0 Avg. Optical Power: 90nW

FWHM = 136 ps Bandwidth=0.5GHz

Am

pliti

ude

(a.u

.)

Time (ps)

HPT without MQW HPT with MQW

MQW structure has much higher optical gain than control SiGe HPT, but poorer speed performance !!

Speed performance of PDs can be improved significantly under low power excitation1

1. Y.-L. Huang and C.-K. Sun, Journal of Lightwave Technology, vol. 18, 2000.


MWP 2003Jin-Wei Shi

0.8 1.2 1.6 2.0 2.40

15

30

45

60

75

90

HPT without MWQ (3GHz) HPT with MQW (0.5GHz)

Bna

dwid

th-R

espo

nsiv

ity

Pro

duct

(GH

z-A

/W)

VCE

(V)

Bandwidth-Responsivity Products of Different Types of HPT

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 !!

MWQ structure has much higher bandwidth-responsivity product than ordinary HPT !!


MWP 2003Jin-Wei Shi

Outline





MWP 2003Jin-Wei Shi

• Two types of SiGe based HPT are demonstrated • MQW structure at B-C junction can improve responsi

vity significantly • Side-wall terminal technique can improve the speed p

erformance 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

Conclusion

Si/SiGe Heterojunction Phototransistor

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