High Speed Surface Illuminated Si Photodiode Using Microstructured Holes for Absorption Enhancements at 900-1000 nm Wavelength

A surface-illuminated silicon photodiode with both high speed and usable external quantum efficiency from 900 to 1000 nm wavelength is highly desirable for intra/inter data center Ethernet communications, high performance computing, and laser radar application. Such Si photodiodes have the potential for monolithic integration to CMOS integrated circuits which can significantly reduce the cost of data transmission per gigabit below one US dollar. To overcome silicon's intrinsic weakness of absorption in these wavelengths, photon-trapping microstructured hole arrays are etched into the silicon surface, and the operational wavelengths of a high-speed silicon PIN photodiode are extended to 1000 nm. In this paper, the design and fabrication of such photon-trapping structures integrated into all-silicon photodiodes with significantly reduced absorption layer thicknesses to achieve high external quantum efficiency and fast response are presented. Different designs and geometries of the submicron holes on the silicon surface can affect the light trapping and ultimately contribute to different external quantum efficiencies at these wavelengths. Some designs are capable of enhancing the absorption by more than an order of magnitude compared to a photodiode without the submicron hole arrays. With the silicon i-layer thickness less than or equal to 2 mu m, the all-silicon photodiode with integrated submicron holes exhibited an external quantum efficiency of more than 40% at 900 nm and greater than 15% at 1000 nm. This thin absorption layer also allows the fast speed of the photodiode with temporal responses of similar to 30 ps at these wavelengths.