THI
D-(6)-1
THz MSM TRAVELING-WAVE PHOTODETECTORS FOR
COMMUNICATIONS AND IMAGING
Chi-Kuang Sun
Graduate Institute of Electro-Optical Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 10617, TAIWAN, R.O.C.
+886-2-2363525 1 ext. 3 19, Fax:+886-2-23677467, E-Mail:[email protected]
Abstract - In this talk. we will review the design, fabrication, andperformance ofsub-teraheriz bandwidth metal-semiconductor-metal traveling-wave photodetectors. Its application in THz bandwidth communicotion and T-ray imaging will be discussed.
High speed photodetectors have been studied extensively in the past decade, owing to their applications in broadband optical communication network and optical generation of high power millimeter/THz waves [l]. In this presentation, we will review the design, fabrication, and performance of sub-terahertz bandwidth metal-semiconductor-metal traveling-wave photodetectors (MSM TWPD) [2]. By utilizing LTG-GaAs as the photo-absorption layer, the dominant propagation microwave mode in a MSM TWPD is “quasi-TEM mode”. The characteristics of low loss and high velocity in the Quasi-TEM mode ensure much higher velocity-match bandwidth compared with that of the p-i-n based TWPD. The fabricated devices exhibit a high-speed performance at 800 nm, with a 0 . 8 ~ ~ impulse current response and a 570GHz bandwidth [2]. This device also provides a record peak-output-voltage-bandwidth product performance (-3OV, 190GHz, 5.7 THz-V) at 800nm [3] under high optical excitation. This is achieved by increasing the photo-absorption volume in a MSM TWPD. Our recently studies have also demonstrated the high speed and high power performances of the fabricated device at the telecommunication wavelength [4] by utilizing mid-gap defect state to conduction band absorption. With a 70pm-long absorption length, its transient impulse response and the corresponding bandwidth at telecommunication wavelength was 1.28 ps (4V bias) 234 GHz 3dB bandwidth [4]. A record peak-output-voltage-bandwidth product of 568 GHz-V was also obtained from the device for the telecommunication regime (160-GHz bandwidth, 3.55-V peak output voltage).
With such a high bandwidth high power performance, this MSM TWF’D can not only be applied for high bandwidth telecommunication, but also as a compact source for efficient generation of THz radiation for molecular imaging and warfare detection. By combining the THz MSM TWPD with a THz antenna, we recently also demonstrated a THz photonic transmitter [l]. The ultrahigh external light-THz conversion efficiency (0.1 1% @ 645 GHz
,
0.02% at 1.6THz) and the edge-coupled structure of our demonstrated devices imply their applications as compact optoelectronic based THz radiators. Some preliminary results on the CW T-ray imaging system will be discussed.
REFERENCES
[ I ] J.-W. Shi, et al., “Edge-Coupled Membrane Terahertz Photonic Transmitters Based on MSM Traveling-Wave Photodetectors,” AppliedPhysics Letters 81, pp. 5108-51 IO (2002).
[2] J.-W. Shi, K.-G. Gan, Y.-J. Yang, Y.-H. Chen, C.-K. Sun, Y.-J. Yang, and J. E. Bowers, “Metal-semiconductor-metal traveling-wave photodetectors,” IEEE Photonic Technology Letters 13, pp. 623-625 (2001).
[3] I.-W. Shi, et al.,.“Ultra-high power-bandwidth product and nonlinear photo-conductance performances of low-temperature-grown GaAs based metal-semiconductor-metal traveling-wave photodetectors,” IEEE
Photonic Technology Letters 14, pp. 1587-1589 (2002).
[4] J.-W. Shi, Y.-H. Chen, K.-G. Gan, Y.-J. Chiu, C.-K. Sun, and I. E. Bowers, “High speed and high power performances of LTG-GaAs based Metal-Semiconductor-Metal Traveling-Wave Photodetectors in 1.3 pm wavelength resme,” IEEE Photonic Technology Letters 14, pp. 363-365 (2002).
0-7803-7766-4/031S17.00 02003 IEEE
