Abstract
Long-absorption-length traveling-wave-photodetectors (TWPDs) are
requisite for high-power and high-speed applications. In the long absorption
length regime, some previously negligible bandwidth limitation factors, such
as microwave loss and boundary reflection, become critical. In this paper,we
calculate each limiting factor for long-absorption-length TWPDs using a
photo-distribute-current model, which can be easily modified to include
different effects comparing with the previous model. The simulated device
structures are low-temperature-grown GaAs (LTG-GaAs)-based
metal-semiconductor-metal (MSM) and n-i-n TWPDs for telecommunication
wavelength applications. Our simulation results indicate that the carrier
trapping time is not the dominant bandwidth limitation factor as in the short
device length regime. The device bandwidth is, on the other hand, strongly
affected by velocity mismatch, frequency-dependent microwave loss, and
boundary reflection. By properly choosing the geometric size of the
transmission line in the MSM TWPD structure, the effect of impedance mismatch
can be eliminated. Also due to the enhanced microwave velocity and a lower
microwave loss, a better bandwidth performance can be found in the MSM TWPD
structure. With a longer carrier trapping time and a higher electrical wave
velocity, high bandwidth-efficiency product can be expected for LTG-GaAs-based
long-absorption length photodetectors.
© 2000 IEEE
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