Group III Nitride Semiconductor Light-Emitting Device With Tilted Side Face
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Solution Overview
Problem
The light extraction efficiency of Group III nitride semiconductor light-emitting devices is limited due to total reflection at the interface between layers of different refractive indices, and existing processing methods for enhancing efficiency, such as mechanical dicing and dry etching, are inefficient and damage-prone, especially when using hard-to-process substrates like sapphire or SiC.
Innovation Solution
A nitride semiconductor light-emitting device with a tilted side face relative to the substrate is created using wet etching, where the dislocation density distribution controls the tilt angle, allowing for enhanced light extraction efficiency without damaging the semiconductor layer, and a groove is formed at the surface to further increase light extraction while preventing short circuits and ensuring uniform current diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mechanical dicing is used to divide the substrate, then the device can be fabricated, but the substrate is hard and difficult to process causing devices to break or crack
Solution Approach 1:
The substrate processing is divided into two stages: first forming a groove to separate the semiconductor layer from the substrate, then applying tension to cleanly separate the substrate. This segmentation allows each step to be optimized independently, avoiding the need for direct mechanical cutting of the hard substrate.
Solution Approach 2:
The groove is formed in advance before substrate separation. This preliminary action creates a predetermined separation path that guides the subsequent tension-based separation process, ensuring clean division without device damage.
2Reliability
If dry etching is used to process the substrate, then mechanical damage is avoided, but processing time is remarkably long reducing productivity
Solution Approach 1:
The patent replaces the mechanical/chemical etching process with a tension-based separation method. By forming a groove and applying tension, the substrate is separated mechanically without the prolonged chemical exposure of dry etching, significantly reducing processing time while maintaining substrate integrity.
3Loss of energy
If the interface is roughened to avoid total reflection, then light extraction efficiency is improved, but processing complexity increases
Solution Approach 1:
Instead of modifying the interface in the horizontal dimension (roughening), the patent introduces a vertical dimension by forming a groove that tilts relative to the substrate surface. This groove structure provides multiple extraction paths for light, improving efficiency without requiring complex interface roughening.
4Loss of energy
If a groove is formed to enhance light extraction, then light extraction efficiency is improved, but short circuits may occur without proper electrode positioning
Solution Approach 1:
The groove is positioned specifically in regions where electrodes will be formed, creating local variations in structure that serve different functions: light extraction enhancement in active regions and electrical insulation in electrode regions. This localized approach allows the groove to provide multiple benefits without causing short circuits.
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 tilted side face and groove structure significantly enhance light extraction efficiency, reduce processing damage, and optimize light emission across large areas without hindering current flow, improving the yield and performance of nitride semiconductor light-emitting devices.
Implementation Method 1
total reflection at the surface of the device... when light is directed toward a layer having a small refractive index from a layer having a great refractive index, light with an angle greater than a critical angle (θc) produces a total reflection at the interface
Implementation Method 2
the refractive index is 2.4, and only light in the Escape Cone, having an apex angle of 24 degrees with respect to the direction vertical to the surface; can be extracted to the outside
Implementation Method 3
it takes long time to process, whereby there arises a problem of a remarkably low productivity. Further, it has been well known that, with the mechanical processing method by a dicing, a layer called a broken layer is formed on the processed surface... Wet etching has been known as a processing method causing less damage
Data Source
AI summary
The present invention aims to enhance the light extraction efficiency of the Group III nitride semiconductor light-emitting device.The inventive Group III nitride semiconductor light-emitting device comprises a substrate; and a Group III nitride semiconductor layer including a light-emitting layer, stacked on the substrate, wherein the side face of the Group III nitride semiconductor layer is tilted with respect to the normal line of the major surface of the substrate.