Mixed Alloy Defect Redirection for Deep UV LED
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Solution Overview
Problem
High dislocation densities and mechanical stresses in deep UV light emitting diodes (LEDs) lead to poor crystal quality and reduced operating lifetime, exacerbated by lattice mismatch between substrates and structural layers, particularly in AlGaN/sapphire templates, which impede efficient light emission and device reliability.
Innovation Solution
A defect redirection layer with varying Al content is introduced between the substrate and the high-Al content MQWH active region, comprising a mixed alloy region of alternating AlN and GaN layers, gradually transitioning from high to low Al content to reduce threading dislocations and strain-induced cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AlGaN template layer is formed on sapphire substrate, then device structure is established, but high dislocation density propagates to active layer reducing light emission efficiency
Solution Approach 1:
A defect redirection layer composed of AlN and GaN layers is introduced as an intermediary between the AlGaN template layer and the InGaN active layer. This intermediary layer redirects threading dislocations away from the growth direction, preventing them from reaching the active layer and maintaining high light emission efficiency.
Solution Approach 2:
The defect redirection layer is segmented into multiple alternating layers of AlN and GaN with different thicknesses. The AlN layers have higher dislocation density while the GaN layers have lower dislocation density, creating a segmented structure that effectively redirects dislocations through the layered configuration.
2Illumination intensity
If high Al content is used in structural layers, then deep UV emission is achieved, but lattice mismatch increases causing mechanical stress and cracking
Solution Approach 1:
The aluminum content parameter is varied through the layer structure. The AlGaN template layer has high Al content (50-70%) for deep UV emission, while the defect redirection layer uses alternating AlN (100% Al) and GaN (0% Al) layers. This parameter change creates a gradual transition that reduces lattice mismatch stress while maintaining the required deep UV emission capability.
Solution Approach 2:
The defect redirection layer is a composite structure combining AlN and GaN materials in alternating layers. This composite approach allows optimization of each layer's properties - AlN provides high Al content for UV emission while GaN provides mechanical strength and lower dislocation density, together resolving the contradiction between deep UV emission and mechanical stress resistance.
Data Source
AI summary
An optical semiconductor device such as a light emitting diode is formed on a transparent substrate having formed thereon a template layer, such as AlN, which is transparent to the wavelength of emission of the optical device. A mixed alloy defect redirection region is provided over the template layer such that the composition of the defect redirection region approaches or matches the composition of the regions contiguous thereto. For example, the Al content of the defect redirection region may be tailored to provide a stepped or gradual Aluminum content from template to active layer. Strain-induced cracking and defect density are reduced or eliminated.