Effectiveness of the pseudowindow for edge-coupled InP-InGaAs-InPPIN photodiodes

We have shown that edge-coupled PIN photodiodes can benefit from the incorporation of a pseudowindow of appropriate thickness. In our experiments, a pseudowindow 2-3 mu m thick can effectively protect the device and antireflection (AR) coating during the cleavage process without sacrificing the device efficiency and speed performance. Also, devices with a pseudowindow could have an increased coupling aperture, which results from the dielectric layers, and thus permits more light to enter the device. The light input facet of the device without a pseudowindow can be severely damaged during the cleavage process and AR coating, which may degrade the device dark current by several orders of magnitude. We also found that, even with partial recovery after rapid thermal annealing, devices without pseudowindows still suffer from damage and the maximum photocurrent is typically restricted to about 3 mA. The typical performance at -5 V of a device with a 100-mu m junction length and a 3-mu m pseudowindow is a responsivity of similar to 0.95 A/W responsivity and a similar to 5.5-GHz bandwidth at a wavelength of 1.3 mu m under 100-mu W illumination.