Abstract

Broadband antireflection layers have been fabricated by two dimensional (2D) photonic crystals (PCs) with tapered pillars on the Si substrate. These PCs have been produced by interference lithography and reactive ion etching (RIE) techniques. The effect of depth and the filling factor (FF) of the PCs on the reflectance magnitude and bandwidth has been investigated. The obtained reflectance was less than 1% in the broad spectral range from 400 to 2100 nm. Our numerical simulation shows the PC pillars slope has an essential effect in the reduction of the reflection. However, our results show that the existence of RIE grasses in the PCs, which are created in the RIE process, does not influence the performance of the antireflection layer. This leads to a simpler fabrication process.

Highlights

  • Fabrication of antireflection layer in many optical sensors such as solar cells and photo detectors is an interesting subject for many investigators [1]–[6]

  • In the antireflection single layer the reflection reduction occurs only in a narrow spectral range where as in multiple antireflection layers, the limitation is choosing suitable material to obtain a large spectral width. Another method for the reduction of the reflectance in these devices is using pores to produce intermediate antireflection layers with suitable refractive index matching between the air and the substrate [11]–[15]

  • We recently present a new method to fabricate an antireflection layer based on the combination of hole array photonic crystals (PCs) and nanoporous structures [19]

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Summary

Introduction

Fabrication of antireflection layer in many optical sensors such as solar cells and photo detectors is an interesting subject for many investigators [1]–[6]. In the antireflection single layer the reflection reduction occurs only in a narrow spectral range where as in multiple antireflection layers, the limitation is choosing suitable material to obtain a large spectral width Another method for the reduction of the reflectance in these devices is using pores to produce intermediate antireflection layers with suitable refractive index matching between the air and the substrate [11]–[15]. Moth eye structure has been used as an antireflection layer in wide bandwidths [16]–[18] This structure is a 2D random array of tapered pillars with a sub-wavelength mean period. These structures have good antireflection performance due to gradual increase the effective refractive index which leads to suitable index matching

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