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

Abstract

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 μm, 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 ∼30 ps at these wavelengths.

Rigorous coupled-wave analysis of absorption enhancement in vertically illuminated silicon photodiodes with photon-trapping hole arrays

“…Several types of microscale and nanoscale structures have been demonstrated in the absorption enhancement of energy conversion systems, such as solar cells [11,12] and thermophotovoltaic devices [13], including nanowires [10,11,14,15], nanorods [16], nanodisks [17], nanocones [18], nanopyramids [19,20], nanoholes [21,22], and other grating structures [23][24][25][26]. Our recent experimental studies [27,28] showed that an array of nanoholes integrated on a 2-μm-thick Si film effectively traps light with wavelengths between 800 and 950 nm and can be used to achieve a high EQE (40-60%) in Si photodetectors while ensuring ultrafast impulse response (full-width at half-maximum) of 30 ps. High-speed Geon-Si photodiodes with photon-trapping holes have also been demonstrated with improved EQE at wavelengths between 1200 and 1800 nm [29].…”

“…The thinner ring and the thicker opened ring are n-ohmic metal on n-mesa and p-ohmic metal on p-mesa, respectively. The detailed fabrication process and EQE characteristics of the photodiodes were reported in our previous studies [27,28]. Photodiodes with hole arrays arranged in hexagonal lattice, as shown in Figure 1D, were fabricated on both bulk Si and SOI wafers with hole diameters ranging from 630 to 1300 nm and periods from 900 to 1700 nm.…”

“…High-speed Geon-Si photodiodes with photon-trapping holes have also been demonstrated with improved EQE at wavelengths between 1200 and 1800 nm [29]. Light-trapping properties of such hole arrays in Si were investigated by finitedifference time-domain method [27] and the effects of hole shape and tapering angle of funnel-shaped holes on the EQE of the photodiodes were analyzed and discussed in detail [27,28]. However, there are still questions that need to be answered: How does the substrate influence the light-trapping properties of the holes, what fraction of light is laterally guided, and where is the guided light mostly confined?…”

Ultralow Optical and Electrical Losses via Metal‐Assisted Chemical Etching of Antireflective Nanograss in Conductive Mesh Electrodes

“…[ 4,5 ] Another method of reducing the reflectance involves the creation of nanotextured semiconductor surfaces. [ 6–10 ] Nanotexturing fabricates subwavelength surfaces on a scale smaller than the wavelength of visible light; this results in discrete refractive‐index changes between the air and the semiconductor. [ 11,12 ] Continuous refractive index changes reduce the reflectance over a broad spectral range and are less influenced by the angle of incidence.…”

Mid-infrared photodetector based on 2D material metamaterial with negative index properties for a wide range of angles near vertical illumination

“…Meanwhile, the applications using light-trapping structures have shown to be effective for enhancing absorption and expanding the operating band into longer wavelengths [9]. The micro-holes structures were used to scatter the normally incident light into the lateral propagation, forming guided modes, and increasing that allows using the thin layers of absorbing material more effective [12][13][14]. The effect was studied for mid-infrared material to increase the wavelength range of the conventional infrared materials [15].…”