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Si/SiGe Heterojunction Phototransistor

Si/SiGe Heterojunction Phototransistor. Jin-Wei Shi 1,* , Z. Pei 1 , Y.-M. Hsu 1 , F. Yuan 2 , C.-S. Liang 1 , Y.-T. Tseng 1 , P.-S. Cheng 1 , C.-W. Liu 1,2 , S.-C. Lu 1 , M.-J. Tsai 1.

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Si/SiGe Heterojunction Phototransistor

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  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 • 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.

  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 LowerOperation 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.

  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 (1.3~1.55mm) photo-absorption can be achieved by using SiGe alloy1 1. H. Lafontaine, et al., Journal of applied physics vol. 86, Aug. 1999.

  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't’t 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 eliminatedby 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-responsivity product than ordinary 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 !!

  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

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