Nitride Semiconductor Light Emitting Device with Etched Surface
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Solution Overview
Problem
Nitride semiconductor light emitting devices face challenges with low light extraction efficiency due to the large refractive index difference between the GaN substrate and air, leading to reflection losses, and conventional protection films degrade when exposed to high-density alkaline solutions, causing defects and efficiency losses during the formation of thin-film LEDs.
Innovation Solution
A semiconductor light emitting device with a tapered stack film structure and a protection film that forms concavities and convexities on the n-type nitride semiconductor layer using alkaline etching, while preventing short-circuiting and leakage by maintaining a continuous protection layer without step separations, enhancing light extraction efficiency and structural reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used for crystal growth, then low cost and high temperature stability are achieved, but low thermal conductivity and inability to form electrodes on the back face result in higher series resistance and poor heat release properties
Solution Approach 1:
The device is divided into two separate substrates: a sapphire substrate for crystal growth and a supporting substrate for electrical connection and heat dissipation. This segmentation allows each substrate to fulfill its optimal function without compromise.
Solution Approach 2:
The nitride semiconductor crystal layer acts as an intermediary that transfers the LED structure from the sapphire substrate to the supporting substrate. This intermediary enables the decoupling of crystal growth requirements from electrical and thermal requirements.
2Reliability
If the surface of the GaN substrate is left flat, then manufacturing is simpler, but the large refractive index difference (2.5 times) between GaN and air causes light reflection and reduces light extraction efficiency
Solution Approach 1:
The flat surface is replaced with a curved surface featuring concavities and convexities. This curvature reduces the refractive index mismatch effect by creating multiple light extraction paths and reducing reflection at the GaN-air interface.
Solution Approach 2:
The surface is modified locally with concavities and convexities rather than changing the entire surface uniformly. This localized modification optimizes light extraction at critical points while maintaining overall structural integrity.
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 solution significantly increases light extraction efficiency by reducing reflection losses and maintaining structural integrity, achieving 1.5 times higher light extraction efficiency compared to conventional methods and preventing defects like cracks and leakage.
Implementation Method 1
formation of a protection film that protects the epitaxial crystals and prevents short-circuiting and leakage
Implementation Method 2
concavities and convexities are formed by roughening the surface through alkaline etching performed on the n-layer
Implementation Method 3
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
Implementation Method 4
the lift-off process may involve a laser lift-off technique utilizing thermolysis of an interface caused by a laser
Data Source
AI summary
Certain embodiments provide a semiconductor light emitting device including: a first metal layer; a stack film including a p-type nitride semiconductor layer, an active layer, and an n-type nitride semiconductor layer; an n-electrode; a second metal layer; and a protection film protecting an outer circumferential region of the upper face of the n-type nitride semiconductor layer, side faces of the stack film, a region of an upper face of the second metal layer other than a region in contact with the p-type nitride semiconductor layer, and a region of an upper face of the first metal layer other than a region in contact with the second metal layer. Concavities and convexities are formed in a region of the upper face of the n-type nitride semiconductor layer, the region being outside the region in which the n-electrode is provided and being outside the regions covered with the protection film.