Abstract
Reflection occurs at an air–material interface. The development of antireflection schemes, which aims to cancel such reflection, is important for a wide variety of applications including solar cells and photodetectors. Recently, it has been demonstrated that a periodic array of resonant subwavelength objects placed at an air–material interface can significantly reduce reflection that otherwise would have occurred at such an interface. Here, we introduce the theoretical condition for complete reflection cancellation in this resonant antireflection scheme. Using both general theoretical arguments and analytical temporal coupled-mode theory formalisms, we show that in order to achieve perfect resonant antireflection, the periodicity of the array needs to be smaller than the free-space wavelength of the incident light for normal incidence, and also the resonances in the subwavelength objects need to radiate into air and the dielectric material in a balanced fashion. Our theory is validated using first-principles full-field electromagnetic simulations of structures operating in the infrared wavelength ranges. For solar cell or photodetector applications, resonant antireflection has the potential for providing a low-cost technique for antireflection that does not require nanofabrication into the absorber materials, which may introduce detrimental effects such as additional surface recombination. Our work here provides theoretical guidance for the practical design of such resonant antireflection schemes.
Highlights
Reflection occurs at the interface between air and a dielectric
We present a theoretical analysis for complete antireflection
Eq (1), which represents a sufficient condition for complete antireflection, represents an optimal condition for light trapping [66,67]
Summary
Reflection occurs at the interface between air and a dielectric. In many applications, for example, solar cells and photodetectors, such a reflection is detrimental to system performance and an effective antireflection strategy is required. We would like the contributions to the reflection amplitude from the direct and resonant pathways to cancel each other This immediately leads to two general considerations: First, the resonance needs to radiate in a balanced fashion to the air and the dielectric sides. If the resonances were to radiate completely into the dielectric substrate, it follows immediately by reciprocity that any incident light from the air side could not excite the resonance In such a case the resonance cannot play any role in the antireflection process. It is interesting to note that, if the periodicity is smaller than the wavelength in the dielectric, i.e., there is only one channel in the dielectric, Eq (12) implies that complete antireflection is only achievable when the resonance decays to the air and the dielectric sides, in consistency with the conclusion in Ref. It is interesting to note that, if the periodicity is smaller than the wavelength in the dielectric, i.e., there is only one channel in the dielectric, Eq (12) implies that complete antireflection is only achievable when the resonance decays to the air and the dielectric sides, in consistency with the conclusion in Ref. [54]
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