Modeling of nanohole silicon pin/nip photodetectors: Steady state and transient characteristics.

Theory is proposed for nanohole silicon pin/nip photodetector (PD) physics, promising devices in the future data communications and lidar applications. Photons and carriers have wavelengths of 1 m and 5 nm, respectively. We propose vertical nanoholes having 2D periodicity with a feature size of 1 m will produce photons slower than those in bulk silicon, but carriers are unchanged. Close comparison to experiments validates this view. First, we study steady state nanohole PD current as a function of illumination power, and results are attributed to the voltage drop partitions in the PD and electrodes. Nanohole PD voltage drop depends on illumination, but series resistance voltage drop does not, and this explains experiments well. Next, we study transient characteristics for the sudden termination of light illumination. Nanohole PDs are much faster than flat PDs, and this is because the former produces much less slow diffusion minority carriers. In fact, most photons have already been absorbed in the i-layer in nanohole PDs, resulting in much less diffusion minority carriers at the bottom highly doped layer. Why diffusion in PDs is slow and that in bipolar junction transistors is quick is discussed in Appendix.