| Summary: | 博士 === 國立臺灣大學 === 光電工程學研究所 === 90 === ABSTRACT
Metal-Semiconductor-Metal Traveling-Wave Photodetectors
by
Jin-Wei Shi
The maximum available power of photodetector decreases as electrical bandwidth increases, and Power-Bandwidth (PB) product is an important figure of merit in the performances of ultra-high speed photodetectors (PDs). PDs with high PB products afford the applications in fiber radio communication system, photoreceiver circuit without electrical amplifier, and the sub-millimeter wave signals generation.
Traveling wave photodetectors (TWPDs) is an attractive option for increasing the PB product over the intrinsic limit of vertically illuminated PDs. By properly guiding the launched optical wave signals and photo-excited microwave signals, the inherent tradeoff between maximum available power and electrical bandwidth limitation is diminished.
In this dissertation, we proposed and demonstrated a novel type of TWPD: low temperature grown GaAs based metal-semiconductor-metal traveling wave photodetectors (LTG-GaAs based MSMTWPDs). We simulated this demonstrated device with the traditional LTG-GaAs based p-i-n TWPDs for comparison purpose by the photo-distributed current model. According to our simulation, MSMTWPD has better microwave guiding properties than p-i-n TWPD, such as lower high-frequency microwave loss, higher microwave velocity, and better impedance matching between external loads and TWPDs. The superior microwave performances and short carrier trapping time of LTG-GaAs in this novel device imply its excellent performance in high PB products.
The theory, fabrication, and measurement of MSMTWPD comprise this thesis work. We established two electro-optic sampling systems to characterize the ultra-high speed performances of MSMTWPD in ~800nm and ~1300nm wavelengths regime. The MSMTWPD displays record high electrical bandwidth (570GHz) and record PB products as large as 5.7 THz-V, which is larger than the previous best-published results (432GHz-V) of Uni-Traveling-Carrier PD (UTC-PD) over ten times. Different nonlinear behaviors of MSMTWPD have also been observed and analyzed in these two wavelength regimes, which are originated from the internal material propriety of LTG-GaAs.
By using the LTG-GaAs based MSMTWPD, we also demonstrated a novel THz photonic transmitter, which can radiate the signals at THz frequency regime by the integration of the MSMTWPD with a slot antenna and proper optical excitation. Record high E/O (electrical power/optical power) conversion efficiency has been demonstrated in the 1.6THz. The obtained conversion efficiency ( ) is larger than the previous best-published results of photomixer at the same operation frequency regime (1.6THz) over ten times ( .
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