Long-wavelength GaInAs/InP graded double heterostructure p-i-n photodi
odes are demonstrated with 3-dB bandwidths over 100 GHz, The heterojun
ction hole trapping problem is significantly improved and the device c
ontact resistivity is greatly reduced by using superlattice graded ban
dgap layers at the hetero-interfaces to reduce the barrier height. Sel
f-aligned processes are used in the device fabrication to reduce devic
e parasitics. Pulsewidths as short as 3.0 ps full-width-at-its-half-ma
ximum (FWHM) for 2 mu m x 2 mu m device are measured by pump-probe ele
ctrooptic sampling. 3-dB bandwidths over 100 GHz are found for 2 mu m
x 2 mu m and 3 mu m x 3 mu m devices. The device with the integrated b
ias tee can be biased without using the external bias tee. The electri
cal resonance between the photodiode and external circuits was reduced
by integrating an impedance matched resistor in parallel with the pho
todiode. The 7 mu m x 7 mu m device with bias tee and matched resistor
has a measured pulsewidth of 3.8 ps and a 3-dB bandwidth over 100 GHz
, The calculated pulse shape based on the saturation velocity model fi
ts well with the measured response. A model for different components o
f the series resistance agrees with the measured area dependence of th
e series resistance.