Diamond Photonic Crystal Slab with Enhanced Photoluminescence Extraction Efficiency
Diamond-based materials exhibit many unique properties, one of them being a broad-band visible photoluminescence (PL) due to a variety of color centers. However, the PL extraction from the diamond layer is inefficient due to high material refractive index. One possibility of increasing the extraction efficiency is by employing a shallow two-dimensional photonic crystal (2D-PhC) at the top of the layer. Then light generated inside the layer and coupled to guided modes can interact with the periodic index modulation and can be Bragg scattered into surrounding air in case that the phase matching condition is fulfilled .
Here we report on enhanced extraction efficiency of intrinsic PL from a nanocrystalline diamond (NCD) layer achieved by introducing the 2D-PhC consisting of NCD columns ordered into the square lattice. A 420 nm thick NCD layer was grown on silica substrate by microwave plasma assisted CVD process . Its surface was then patterned employing electron beam lithography into the form of 2D-PhC, the dimensions of which were chosen carefully such that they allow effective light extraction within the whole visible region.
Spectrally resolved micro-PL measurements, detected within a broad angle from the top of the structure, revealed up to 6-fold enhancement of PL from the PhC compared to the uncorrugated layer . Angle and spectrally resolved measurements of PL and optical transmittance allow us to map the photonic band diagram of our sample . The results show good agreement with the computed photonic band diagram suggesting that mainly the PhC effect contributes to the PL enhancement. To the best of our knowledge, this is the first observation of an effect of this kind in NCD and is promising for taking advantage of the diamond PL in optical, optoelectronic, and biological applications.
KeywordsExtraction Efficiency Electron Beam Lithography Light Extraction Nanocrystalline Diamond Diamond Layer