Nitride Semiconductor Light Extraction via Angled Substrate Structures
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Solution Overview
Problem
Current semiconductor light emitting devices using nitride semiconductors face challenges in achieving high crystallinity and luminous efficiency due to light trapping in GaN semiconductor layers on sapphire substrates, where the refractive index difference leads to inefficient light extraction.
Innovation Solution
A nitride semiconductor device is developed with a single crystal substrate featuring structural bodies such as protrusions or recesses on its surface, where the arrangement of these structural bodies is angled relative to the crystal lattice by 1-10 degrees, enhancing light extraction efficiency and crystallinity by reducing edge dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a semiconductor thin film structure made of GaN is stacked on a sapphire substrate, then the device structure is simple and easy to manufacture, but the light extraction efficiency is low due to great refractive index difference causing light trapping
Solution Approach 1:
The patent introduces protrusions or recesses with curved surfaces on the sapphire substrate to modify light extraction. The curved geometry helps to reduce total internal reflection and improve light coupling between the GaN layer and sapphire substrate, thereby increasing light extraction efficiency while maintaining the simplicity of the basic device structure
Solution Approach 2:
The patent adds vertical dimension features (protrusions and recesses) to the otherwise planar substrate surface. This dimensional modification creates additional light extraction pathways and reduces light trapping effects without fundamentally changing the horizontal device architecture, thus maintaining ease of manufacture while improving optical performance
2Loss of energy
If an unevenness is provided in the surface of the sapphire substrate to increase light extraction efficiency, then the light extraction efficiency is improved, but the crystallinity and edge dislocation density are adversely affected
Solution Approach 1:
The patent carefully controls the parameters of the protrusions and recesses, including their depth (1-10 μm), width (1-10 μm), and spacing (10-100 μm), to optimize light extraction while minimizing impact on crystallinity. By adjusting these geometric parameters within specific ranges, the patent achieves a balance between optical performance and crystal quality
Solution Approach 2:
The patent introduces localized surface modifications (protrusions and recesses) only in specific regions where light extraction enhancement is needed, rather than uniformly altering the entire substrate. This localized approach allows light extraction improvement while preserving the overall crystalline structure and minimizing edge dislocation density in critical areas
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 angled structural bodies improve light extraction efficiency and crystallinity, resulting in higher internal quantum efficiency and increased light output, as demonstrated by the nitride semiconductor device achieving 24.5 milliwatts of light output compared to 23.7 milliwatts from a reference example.
Implementation Method 1
the light produced by the semiconductor layer tends to be trapped easily in the GaN semiconductor layer because the refractive index differs greatly between the GaN semiconductor and the sapphire
Data Source
AI summary
According to one embodiment, a nitride semiconductor device includes a substrate and a semiconductor functional layer. The substrate is a single crystal. The semiconductor functional layer is provided on a major surface of the substrate and includes a nitride semiconductor. The substrate includes a plurality of structural bodies disposed in the major surface. Each of the plurality of structural bodies is a protrusion provided on the major surface or a recess provided on the major surface. An absolute value of an angle between a nearest direction of an arrangement of the plurality of structural bodies and a nearest direction of a crystal lattice of the substrate in a plane parallel to the major surface is not less than 1 degree and not more than 10 degrees.