Quasi-Guided-Mode Reflector for Semiconductor Light Extraction
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Solution Overview
Problem
Conventional semiconductor light-emitting devices face challenges in achieving high photon extraction efficiency due to the large refractive indices of semiconductor materials, leading to trapped light through total internal reflection, which requires numerous photon bounces to escape, increasing device complexity and cost.
Innovation Solution
A semiconductor light-emitting device incorporating a quasi-guided-mode (QGM) structure with a waveguide layer, cladding layer, and scattering elements positioned near the active layer, redirecting laterally propagating light perpendicularly to enhance extraction efficiency and reduce the number of internal reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional semiconductor light-emitting devices are used with standard refractive index materials, then the device structure remains simple, but photon extraction efficiency is low due to total internal reflection trapping light
Solution Approach 1:
The patent introduces a quasi-guided-mode (QGM) structure as an intermediary component between the active layer and the external environment. This QGM structure includes a waveguide layer with specific refractive index characteristics that mediates the transition of light from the high-index semiconductor to the low-index external medium, enabling efficient photon extraction without requiring complex multi-layer conventional structures
Solution Approach 2:
The patent changes the refractive index parameter by using a waveguide layer with refractive index nw where n2 < nw < n1 (n1 being the semiconductor refractive index and n2 being the external medium refractive index). This parameter change creates quasi-guided modes that enable light extraction while maintaining structural simplicity
2Device complexity
If conventional light extraction methods are used, then fewer structural components are needed, but the number of internal redirections and reflections per photon increases
Solution Approach 1:
The QGM structure acts as an intermediary that directly guides photons from the active layer to the external medium, eliminating the need for multiple internal redirections and reflections. The waveguide layer creates quasi-guided modes that transport light efficiently with minimal bounces, reducing the time loss while maintaining simple device structure
Solution Approach 2:
The patent replaces the mechanical system of multiple internal reflections and redirections with an optical field-based quasi-guided mode transport mechanism. Instead of relying on photons bouncing multiple times through conventional interfaces, the evanescent field coupling in the QGM structure provides a direct transport path
3Ease of manufacture
If the QGM structure is positioned far from the active layer, then manufacturing alignment is easier, but near-field coupling and Purcell enhancement are reduced
Solution Approach 1:
The patent segments the QGM structure into distinct functional layers (waveguide layer, cladding layer) with the waveguide layer positioned in near-field proximity to the active layer. This segmentation allows the critical near-field coupling function to be performed by the waveguide layer while other layers provide structural support and optical confinement
Solution Approach 2:
The patent applies local quality by positioning only the waveguide layer in near-field proximity to the active layer where strong coupling is needed, while the cladding layer extends further out to provide optical confinement. This localized near-field positioning maximizes coupling efficiency without requiring the entire structure to be in tight alignment
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 QGM structure enhances photon extraction efficiency, reduces the number of internal redirections, and increases the fraction of light within the escape cone, resulting in improved radiated emission and Purcell factor, while minimizing optical loss and device complexity.
Implementation Method 1
a plurality of scattering elements positioned on or in the waveguide layer. The scattering elements are arranged to redirect a fraction of output light propagating within the device, including in laterally propagating quasi-guided modes supported by the QGM structure, to propagate perpendicularly toward the device exit surface
Implementation Method 2
The second semiconductor layer is sufficiently thin so that the QGM structure is in near-field proximity to the active layer relative to the vacuum wavelength λ0. Near-field proximity of the QGM structure to the active layer, and structural arrangement of the QGM structure, can result in the device exhibiting one or more of: (i) a relatively enhanced Purcell factor, (ii) a relatively increased fraction of output light propagating within a device escape cone
Implementation Method 3
The QGM structure includes (i) a waveguide layer of substantially transparent dielectric material positioned against the back surface of the second semiconductor layer and having an effective refractive index higher than that of the second semiconductor layer, (ii) a cladding layer of substantially transparent dielectric material positioned against a back surface of the waveguide layer and having an effective refractive index lower than that of the waveguide layer
Implementation Method 4
The device exit surface can include an anti-reflection layer or coating
Data Source
AI summary
A light-emitting device includes a semiconductor diode structure, a quasi-guided-mode (QGM) structure against the back of the diode structure, and a reflector against the back of the QGM structure. The diode structure includes first and second doped semiconductor layers and an active layer between them; the active layer emits output light at a nominal emission vacuum wavelength λ0 to propagate within the diode structure. The QGM structure includes a waveguide layer, a cladding layer, and scattering elements, and is in near-field proximity to the active layer relative to λ0. At least a portion of the output light, propagating perpendicularly within the diode structure relative to a device exit surface, exits the diode structure as device output light. The scattering elements redirect output light propagating within the device, including in laterally propagating quasi-guided modes supported by the QGM structure, to propagate perpendicularly toward the device exit surface.