Enhanced Visible Light Sensitivity by Gold Line-and-Space Grating Gate Electrode in Thin Silicon-On-Insulator p-n Junction Photodiode

A new type of thin silicon-on-insulator (SOI) p-n junction photodiode (PD) with gold (Au) line-and-space grating gate electrode is proposed and demonstrated to have high quantum efficiency (QE) at visible wavelengths. This PD is similar to our previous one in the use of the grating and the metal-oxide-semiconductor structure but is very different in the use of the separate binary grating instead of the continuous one and the thick gate oxide. As a result, the diffracted light from the grating efficiently couples with the lateral propagation mode in the SOI slab waveguide, leading to an external QE one order of magnitude higher than that without the grating. In addition, the importance of the proper setting of the gate and substrate biases is shown so as to realize the wide depletion region and resultant high QE.