GaN Rods on Silicon Substrates for LED Manufacturing
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Solution Overview
Problem
Gallium nitride (GaN) light emitting devices grown on silicon substrates suffer from high defect density and cracking due to lattice and thermal expansion mismatches, leading to reduced light emission efficiency, and silicon substrates absorb light, necessitating additional processing steps.
Innovation Solution
A method involving the formation of GaN rods on a silicon substrate with an insulating and reflective layer stack, followed by lateral growth of n-GaN and subsequent deposition of active and p-GaN layers, reduces defect density and cracks, and includes an optional process using ZnO rods for further defect reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN light emitting cells are grown on a silicon substrate, then manufacturing cost is reduced and larger substrate diameters are enabled, but a high number of cracks form due to lattice and thermal expansion mismatches
Solution Approach 1:
The patent divides the continuous GaN layer into discrete GaN rods grown on the silicon substrate. This segmentation reduces the overall stress accumulation by creating isolated growth regions, preventing crack propagation that would occur in a continuous layer, thus enabling reliable devices on cost-effective silicon substrates
Solution Approach 2:
The patent introduces an insulating layer as an intermediary between the silicon substrate and the GaN rods. This intermediate layer acts as a stress buffer that decouples the thermal expansion mismatch between silicon and GaN, reducing crack formation while maintaining the cost advantages of silicon substrates
2Ease of manufacture
If GaN light emitting cells are grown on a silicon substrate, then manufacturing cost is reduced, but the silicon substrate absorbs light emitted by the GaN cells
Solution Approach 1:
The patent extracts the problematic silicon substrate absorption effect by growing GaN rods that extend through the insulating layer, positioning the active light-emitting regions above the substrate plane where they are less affected by substrate absorption, thereby maintaining cost-effectiveness while improving light emission efficiency
3Length of moving object
If GaN layer thickness is increased to achieve desired device performance, then device functionality is improved, but the number of cracks increases
Solution Approach 1:
By segmenting the GaN structure into discrete rods rather than a continuous thick layer, the patent enables achieving desired device performance through increased rod height without the linear increase in crack density that would occur in a continuous layer, as each rod independently manages stress
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 achieves a GaN layer with low defect density and improved luminous efficiency comparable to GaN grown on sapphire substrates, while allowing for cost-effective manufacturing using larger silicon substrates and enhancing light emission by reducing substrate absorption.
Implementation Method 1
The ZnO rods may be removed by thermal decomposition at a temperature of about 600° C. to about 900° C.
Implementation Method 2
forming a GaN covering on outer peripheries of the ZnO rods via GaN deposition; The GaN deposition may occur at a temperature lower than a thermal decomposition temperature of the ZnO rods
Data Source
AI summary
A method of manufacturing a semiconductor light emitting device may include forming an insulating layer on a substrate, forming a plurality of first holes in the insulating layer, forming a plurality of GaN rods in the plurality of first holes, and laterally growing an n-GaN layer on the plurality of GaN rods.