Edge-coupled InGaAs P-I-N photodiode with a pseudowindow

We have experimentally verified that the incorporation of a pseudowindow with appropriate thickness can be advantageous for avoiding excessive surface leakage and improving quantum efficiency of edge-coupled InP/InGaAs/InP p-i-n photodiode (EC-PD). The window, which results in a passive facet, effectively protects the diode during facet cleavage and facet coating. Typical leakage density at -5 V of a facet-coated EC-PD with 2-/spl mu/m pseudowindow is lower than 1.5/spl times/10/sup -6/ A/cm/sup 2/ (30 pA). Also, due to the dielectric layers and the absence of alloyed metal/semiconductor interface on top of the window, the EC-PD could have an enlarged coupling aperture and reduced dissipative absorption. Nevertheless, for low-bias operation (e.g., /spl les/5 V), window thickness should be accurately controlled, otherwise excessive absorption in undepleted region would degrade the device performance. The optimal window thickness, which in fact is affected by experimental parameters (e.g., diffusion time), was determined to be about 2 to 3 /spl mu/m in this study according to the measurement results of efficiency and bandwidth.