MWP 2003 Jin-Wei Shi 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 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 2003 Jin-Wei Shi 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 Outline

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

MWP 2003 Jin-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) OEIC 1 !! Lower fabrication cost than p-i-n+HBT OEIC Analog fiber communication application of HPT 2 Clock recover O-E circuit, O-E Mixer Speed is critical issue for the application of HPT!! Optical f T for analog fiber application 1 Electrical f 3dB for digital fiber application We will demonstrate a novel method to improve the gain-bandwidth product of HPT in this presentation !! Photo-transistor for Fiber Communication Application 1. H. Wang, et al., IEEE Trans. Microwave Theory Tech., vol. 34, Dec H. Kamitsuna, et al., IEEE Trans. Microwave Theory Tech., vol. 49, Oct

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/speed 2, 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 HBT 3 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 B. Jagannathan, et al., IEEE Electron Device Letters, vol. 23, May, Z. Ma, et al., IEEE Trans. Microwave Theory Tech., vol. 50, April, 2002.

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

MWP 2003 Jin-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 (1.3~1.55  m) photo-absorption can be achieved by using SiGe alloy 1 MQW at B-C Junction !! The same as SiGe HBT !! 1. H. Lafontaine, et al., Journal of applied physics vol. 86, Aug

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

MWP 2003 Jin-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

MWP 2003 Jin-Wei Shi f T f max of Si/SiGe HPT with/without MQW f t is the key parameter at the application of analog circuit QW structure has higher f max but lower f t than ordinary HBT due to the extra thickness of MQW at collector !! High conversion gain of SiGe based O/E mixer 1 can be expected due to high f t and high  1. H. Kamitsuna, et al., IEEE Trans. Microwave Theory Tech., vol. 49, Oct

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

MWP 2003 Jin-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 wavelength 1 Higher responsivity can be expected by improving coupling optics!! Excitation Wavelength: 850nm 1. B. Yang, et al., IEEE Photonic Technology Letters, vol. 15, May Photo-DC Measurement Results- with/without QW structure

MWP 2003 Jin-Wei Shi Responsivity enhancement 1 & Photo-absorption bleach 2 at near breakdown voltage !! Optoelectronic Mixer 1, 2 1. E. Suematsu and N. Imai, IEEE Trans. Microwave Theory Tech., vol. 44, pp , M. Tsuchiya, and T. Hosida, IEEE Trans. Microwave Theory Tech., vol. 47, Photo-DC Measurement Results- Nonlinear Behaviors at Near Breakdown Region

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

MWP 2003 Jin-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 technique 1,2,3 –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 gain 1,2 !! –What is the optimum solution? Speed Performance of HPT 1. M. Y. Frankel, et. al., IEEE Journal of Quantum Electronics, vol. 31, Feb T. F. Carruthers, et. al., Appl. Phys. Lett., vol. 63, no. 14, Oct S. Chandrasekhar, et. al., IEEE Electron Device Letters, vol. 12, Oct

MWP 2003 Jin-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 2003 Jin-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 2003 Jin-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 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!!

MWP 2003 Jin-Wei Shi FWHM enhancement : 2.5 ns  0.85 ns Photocurrent reduction : 15  A  8.7  A Superior Performance of HPT without MQW by using Side-Wall Terminal Technique FWHM enhancement : 2.5 ns  0.95 ns Photocurrent 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 *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 2003 Jin-Wei Shi *Side-Wall contact terminal is more useful than base terminal at quantized structure !! FWHM enhancement : 7.7 ns  1 ns Photocurrent reduction : 90  A  45  A FWHM enhancement : similar to 7.7 ns Photocurrent 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 2003 Jin-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 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 PDs 1 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 , Oct Advantages of Side-Wall Terminal

MWP 2003 Jin-Wei Shi High Speed Performances by Using Side-Wall Termination Technique under low power illumination HPT without MQWHPT 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 excitation 1 1. Y.-L. Huang and C.-K. Sun, Journal of Lightwave Technology, vol. 18, 2000.

MWP 2003 Jin-Wei Shi 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 f t 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 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

MWP 2003 Jin-Wei Shi 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 Conclusion