Semiconductor Light Emitting Device Surface Texturing
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Solution Overview
Problem
Conventional nitride semiconductor light emitting devices face challenges with low light extraction efficiency due to the large difference in refractive index between the GaN substrate and air, which is exacerbated by the laser lift-off process, and the inability to form larger concavities and convexities on the surface using alkaline etching.
Innovation Solution
A method involving the formation of concavities and convexities on the surface of the n-type nitride semiconductor layer using wet etching with an alkaline solution after forming n-electrodes, allowing for the creation of both large and small features, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a sapphire substrate is used for growing InGaN-based crystals, then the crystalline quality can be improved with a low-temperature buffer, but the thermal conductivity is low and electrodes cannot be formed on the back face side
Solution Approach 1:
The device is divided into two separate substrates: a sapphire substrate for growing high-quality InGaN crystals and a separate heat sink substrate (Cu, Al, or Si) for thermal management and back-side electrode formation. The InGaN crystal layer is transferred from the sapphire substrate to the heat sink substrate, allowing each substrate to optimize its specific function without compromise.
2Ease of manufacture
If both p- and n-electrodes are formed on the nitride semiconductor side, then the device can be manufactured, but the series resistance increases and heat release properties deteriorate
Solution Approach 1:
The electrode configuration transitions from a planar arrangement (both electrodes on the same face) to a three-dimensional arrangement (electrodes on opposite faces). The n-electrode is formed on the back face of the heat sink substrate while the p-electrode remains on the front face, enabling vertical current flow that reduces series resistance and improves heat dissipation.
3Ease of manufacture
If a laser lift-off process is used to transfer crystals, then the transfer can be achieved, but the light reflection from the boundary face lowers the light extraction efficiency
Solution Approach 1:
The originally flat extraction surface is transformed into a curved surface with concavities and convexities. This curvature creates multiple light extraction paths and reduces the impact of Fresnel reflection by varying the angle of incidence across the surface, thereby improving light extraction efficiency despite the refractive index mismatch.
4Illumination intensity
If alkaline etching is performed to form concavities and convexities, then the light extraction efficiency can be improved, but the sizes of the concavities and convexities cannot be made larger
Solution Approach 1:
The etching parameters are optimized to achieve the desired concavity/convexity dimensions. By adjusting etching time, temperature, and alkaline solution concentration, the process produces features with heights of 1-3 μm and diameters of 1-10 μm, which are larger than conventional etching results while maintaining light extraction efficiency.
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 method significantly increases light extraction efficiency by forming concavities and convexities with height differences of 1 to 3 μm and 300 nm or less, reducing reflection and improving the overall emission intensity of semiconductor light emitting devices.
Implementation Method 1
performing wet etching on the upper face of the n-type nitride semiconductor layer with the use of an alkaline solution, to form concavities and convexities
Implementation Method 2
the difference in refractive index between the surface of a GaN substrate and the external air is as large as 2.5 times where only a laser lift-off process has been carried out, and the light reflection from the boundary face lowers the light extraction efficiency
Data Source
AI summary
Certain embodiments provide a method for manufacturing a semiconductor light emitting device, including: providing a first stack film on a first substrate, the first stack film being formed by stacking a p-type nitride semiconductor layer, an active layer having a multiquantum well structure of a nitride semiconductor, and an n-type nitride semiconductor layer in this order; forming an n-electrode on an upper face of the n-type nitride semiconductor layer; and forming a concave-convex region on the upper face of the n-type nitride semiconductor layer by performing wet etching on the upper face of the n-type nitride semiconductor layer with the use of an alkaline solution, except for a region in which the n-electrode is formed.