InGaAs Surface Normal Photodiode for 2 $\mu \text{m}$ Optical Communication Systems

High bandwidth 2- $\mu \text{m}$ wavelength surface normal p-i-n photodiodes using a high indium-content InGaAs strain-relaxed absorbing layer clad by p- and n-doped AlInGaAs layers are realized. A parabolic grading was used to relax the lattice constant from that of the InP substrate. We compare structures with different p-doping profiles and absorber thicknesses to achieve a 3-dB bandwidth of $\sim 10$ GHz while maintaining a photoresponsivity of 0.93 A/W. A clear opening of the 10-Gb/s eye pattern was obtained with an input power of −3.07 dBm. By temperature-control of the mesa passivation process, the device leakage was reduced to $0.52~\mu \text{A}$ at −5 V bias.