Optimization of light trapping micro-hole structure for high-speed high-efficiency silicon photodiodes

Abstract

We optimized micro-holes in a thin slab for fast Si photodetectors at wavelength 800-950nm. Lateral modes are shown to be responsible for the effective light trapping. Small disorder and cone hole shapes helped achieve uniform quantum efficiency in a wide wavelength range. SummeryThe Si pin PDs at the short-reach multimode datacom wavelengths of 840-860 nm and at a short wavelength division multiplexing (SWDM) band of 850-950 nm could facilitate the integration [1] and reduce the cost. Our recent study [2] showed experimentally that a microstructure can increase the Si PDs quantum efficiency (QE) so that less than 2 micron intrinsic (i) layer can show the QE>50% with data rate 20 Gb/s for wavelength 800-950nm . In this study we analyze the modes in the structure numerically in order to optimize shape and size of the holes for better QE.

Enhanced Quantum Efficiency and Reduction of Reflection for MSM Photodetectors with Nano-Structured Surface

“…Two basic geometries were studied: Si thickness t=1000nm with the inverted pyramids arranged in square lattice between electrodes with period p=500nm and side a=500nm; and the thickness t=2000nm, p=1000nm, a=700nm. As it was shown in [2][3][4] the holes array supports a set of modes with wave vectors in z direction, kz and kc in x-y plane. Each hole couples the vertically incident light into the x-y plane.…”

“…The Si MSM photodetectors (PDs) at the short-reach multimode datacom wavelengths of 840-860 nm and at a short wavelength division multiplexing (SWDM) band of 850-950 nm could facilitate the integration [1] and reduce the cost. Our study [2,3] showed theoretically and experimentally that a nano-or micro-structure can increase the Si PDs quantum efficiency (QE) for pin diodes so that less than 2 microns intrinsic (i) layer can show the QE>50% with data rate 20 Gb/s for wavelength 800-950nm. In this study we use nanoholes to reduce the reflection and increase QE in MSM PDs.…”

Quantum Efficiency Enhancement of Mid Infrared Photodetectors with Photon Trapping Micro-Structures

“…The field distribution around the cylindrical holes (Fig.1e) shows the lateral modes between the holes. The tapered or inverter pyramids shape had smaller reflection due to the effect is similar to the Lambertian reflector that helps to trap infrared radiation [5]. The micro-holes also provide better absorption in wider region.…”

“…The lateral modes with larger kc can have full reflection from the bottom of the PD and they can form modes guided in the x-y plane in b-AsP layer. The lateral modes [4,5] in xy plane causing higher absorption. The FDTD simulation for the inverted pyramids holes in SiO2 cover with period 2000nm and diameter of 1700nm ( Fig.1d green curve) shows some absorption increase over flat cover (Fig.1d, black curve).…”

“…The same holes in Si cover produced much better absorption enhancement (Fig.1d, red curve). The lateral modes are responsible for the QE enhancement [5]. The longer the light propagate into b-As layer and the better it confined in it the better is the absorption for a wider range of the wavelength.…”