Single-Sided PBG Bragg Reflector for Light Extraction
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Solution Overview
Problem
Existing SiOx light emitting devices suffer from poor light emission efficiencies into air due to light loss in highly doped silicon substrates and non-collimated emission through ITO layers, making it challenging to achieve high collection efficiencies for free space optical communications and coupling light into planar waveguides.
Innovation Solution
A light emitting device with a single-sided photonic bandgap Bragg reflector is introduced, featuring a heavily doped silicon bottom electrode, a Si-containing dielectric layer with embedded Si nanoparticles, and a transparent ITO top electrode, along with a PBG Bragg reflector that includes periodic bi-layers of materials with different refractive indexes to enhance light collection and waveguide coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If SiOx layers are placed directly on Si substrate, then device structure is simple, but light extraction efficiency to air is poor (around 19.7%) due to light loss in Si substrate
Solution Approach 1:
The device structure is segmented by introducing a distributed Bragg reflector (DBR) layer between the SiOx active layer and the Si substrate. This segmentation creates distinct functional zones: the DBR layer with periodic high/low refractive index layers separates the light emission region from the substrate, enabling independent optimization of light extraction and structural integrity.
Solution Approach 2:
The DBR layer employs composite material structure with alternating high refractive index (Si, SiN) and low refractive index (SiO2) layers. This composite structure creates photonic bandgap effects that reflect specific wavelength ranges back into the SiOx layer, significantly enhancing light extraction efficiency to air while maintaining compatibility with standard semiconductor materials.
2Loss of energy
If alignment between light source and photodetector is required, then collection efficiency can be improved, but system complexity and alignment difficulty increase
Solution Approach 1:
The DBR layer creates an optically enhanced emission region that increases the effective solid angle of light emission. By achieving near-omnidirectional emission enhancement through the photonic bandgap effect, the system reduces the need for precise angular alignment between light source and photodetector, effectively creating an equipotential emission pattern in all directions.
Solution Approach 2:
The invention transitions from relying on one-dimensional precise angular alignment to utilizing the third dimension of omnidirectional emission enhancement through the DBR structure. The periodic layering in the vertical dimension creates photonic bandgap effects that enhance emission in all lateral directions, adding dimensional freedom to the optical coupling.
3Ease of manufacture
If no waveguiding mechanisms are provided, then device structure is simple, but light coupling into planar waveguides is inefficient
Solution Approach 1:
The DBR layer structure serves multiple functions simultaneously: it enhances light extraction to air for free-space optical communication, provides waveguiding mechanisms for on-chip optical interconnectors, and enables microfluidics bio/chemical sensing applications. This multi-functionality is achieved through the photonic bandgap effects that can guide and confine light in various configurations.
Solution Approach 2:
The DBR layer acts as an intermediary between the SiOx light source and the planar waveguide. The periodic high/low refractive index structure creates evanescent wave coupling that facilitates efficient energy transfer from the vertical cavity to the lateral waveguide mode, overcoming the mismatch between the two optical configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly improves light collection efficiencies into air and waveguide coupling, reducing alignment requirements for free space optical communications and enabling efficient light transfer into planar waveguides, thereby enhancing signal quality and integration with CMOS IC devices.
Implementation Method 1
a photonic bandgap (PBG) Bragg reflector underlies the Si bottom electrode
Implementation Method 2
The PBG Bragg reflector includes at least one periodic bi-layer of films with different refractive indexes
Implementation Method 3
The PL spectrum peaks at 750 nm for 5 nm-Si particles embedded in SiOx
Implementation Method 4
The EL spectrum is shown in FIG. 14B shows an EL spectrum that is slightly broader than the corresponding PL spectrum from the same materials
Data Source
AI summary
Light emitting and waveguide devices with single-sided photonic bandgaps are provided. The light emitting device is formed from a heavily doped silicon (Si) bottom electrode, and a Si-containing dielectric layer embedded Si nanoparticles overlying the bottom electrode. A transparent indium tin oxide (ITO) top electrode overlies the Si-containing dielectric layer, and a photonic bandgap (PBG) Bragg reflector underlies the Si bottom electrode. The PBG Bragg reflector includes at least one periodic bi-layer of films with different refractive indexes. The single-sided photonic bandgap planar waveguide interface is formed from a planar waveguide and a PBG Bragg reflector underlying the planar waveguide.