Light Emitting Device Reflective Metal Layer Relocation
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Solution Overview
Problem
Conventional light emitting devices face issues with light loss due to absorption by transparent electrodes and pads, limited thickness of p-type GaN layers, and etching damage to reflective metal layers, which reduces light extraction efficiency and increases the risk of short circuits.
Innovation Solution
A light emitting device design featuring a substrate with spaced-apart light emitting cells, an intermediate insulating layer, and reflective metal layers between the cells and the substrate, along with wires connecting the cells in series, to minimize light absorption and prevent short circuits, while allowing for thicker nitride semiconductor layers and improved light reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transparent electrodes and pads are formed on the light emission surface, then electrical connection is achieved, but light absorption increases and light emitting efficiency decreases
Solution Approach 1:
The patent extracts the transparent electrodes and pads from the light emission surface and relocates them to the side walls and bottom surface of the light emitting device. This allows the light emission surface to be free of light-absorbing elements while maintaining electrical connections through the relocated electrodes on the side walls and bottom surface.
2Loss of energy
If the reflective metal layer is positioned close to the active layer, then light reflection efficiency improves, but the distance for light travel increases and light loss increases
Solution Approach 1:
The patent transitions the reflective metal layer from a bottom-surface position to side wall positions, changing the spatial dimension of light reflection. This allows light to be reflected earlier in its path through the device, reducing the distance light travels through lossy materials while still achieving effective light extraction.
3Loss of energy
If the p-type GaN layer is made thick to enable light emission surface formation, then light extraction efficiency improves, but the layer cannot be formed thick due to high resistance
Solution Approach 1:
The patent extracts the light emission function from the top surface of the p-type GaN layer and relocates it to the side walls. This allows the p-type GaN layer to be made thick for better light extraction without being constrained by the need to form a thin layer for top-surface emission, as light now exits through the side wall surfaces.
4Loss of energy
If etching is performed to form light emission surface, then light extraction efficiency improves, but the reflective metal layer suffers etching damage
Solution Approach 1:
The patent extracts the reflective metal layer from the bottom surface where it would be exposed to etching processes, and relocates it to the side walls. This positioning allows the formation of light emission surfaces through etching without exposing the reflective metal layer to damaging etchants, preserving its integrity and reflectivity.
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
Enhances light extraction efficiency by reducing light loss to the substrate and preventing short circuits, while maintaining the reflective metal layer's integrity and improving the overall light emitting performance.
Implementation Method 1
a reflective metal layer is generally formed on the bottom surface of the sapphire substrate to reflect the light that travels toward the lower portion of the light emitting device
Data Source
AI summary
Disclosed are a light emitting device and a method of fabricating the same. The light emitting device comprises a substrate. A plurality of light emitting cells are disposed on top of the substrate to be spaced apart from one another. Each of the light emitting cells comprises a first upper semiconductor layer, an active layer, and a second lower semiconductor layer. Reflective metal layers are positioned between the substrate and the light emitting cells. The reflective metal layers are prevented from being exposed to the outside.