Monolithically Integrable SQW High Speed Waveguide Photodiode With InGaAs/InP Graded Bandgap QW and SL Cladding

A monolithically integrable p-i-n waveguide photodiode (WGPD) has been theoretically analyzed and experimentally demonstrated. The p-i-n WGPD comprises of a single quantum-well absorbing layer, graded band gap quantum well architecture along with superlattice cladding designed through electrical, optical, and RF optimizations. Better tolerance and responsivity are achieved by integrating fiber-matched waveguide to the WGPD using a laterally tapered waveguide interconnect. A 30
$ \mu$
m long WGPD exhibits a low dark current density of 5.31 mA/
$cm^{2}$
at −3 V due to the existence of near mid-gap traps. The electrons and holes tunneling at higher electric fields further enhance the dark current generation. The WGPDs with 3
$\mu$
m mesa width and lengths of 10, 20, 30, 40, and 50
$\mu$
m are fabricated, studied electrically and optically, for a maximum responsivity of 0.56 A/W. Instrument limited 20 GHz 3-dB bandwidths at 1550 nm is demonstrated, which are better than any PDs with i-QW architecture. 3-dB bandwidth of over 100 Gbps is estimated from the measured scattering parameter and simulation. This device is suitable for low dark current, high responsivity, and high bandwidth performance, allowing integration of other optical components with a high-speed photodiode, without any regrowth requirements.