110-GHZ GAINAS INP DOUBLE-HETEROSTRUCTURE P-I-N PHOTODETECTORS/

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.