Clover and H-Shape Contact Layers for UV Nitride LEDs
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Solution Overview
Problem
Nitride-based light emitting diodes and lasers face performance degradation as wavelength reduces into the ultraviolet range due to high resistivity in AlGaN contact layers, leading to current crowding and non-uniform light distribution, which is exacerbated by the conventional circular shape that is not conducive to efficient packaging.
Innovation Solution
The use of a contact layer with a clover shape having at least a third order axis of symmetry or an H-shape, which provides improved current distribution and packaging efficiency by reducing lateral resistance and current crowding, allowing for more uniform light emission and efficient packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the Al molar fraction in the AlGaN contact layer is increased to reduce UV light absorption, then the light absorption decreases, but the resistivity increases leading to current crowding
Solution Approach 1:
The contact layer is divided into multiple segments or regions with different Al molar fractions. The contact layer includes a first contact layer region with a first Al molar fraction and a second contact layer region with a second Al molar fraction, where the Al molar fraction varies laterally across the contact layer. This segmentation allows different regions to have optimized properties: some regions with lower Al content for better conductivity while others with higher Al content for lower absorption.
Solution Approach 2:
The contact layer is designed with spatially varying local properties, specifically the Al molar fraction varies laterally across different regions of the contact layer. This local quality variation allows each region to be optimized for its specific function: regions closer to the light emission area have higher Al content to reduce absorption, while regions for current injection have lower Al content to maintain low resistivity.
2Ease of manufacture
If a conventional circular shape is used for the LED, then the manufacturing is simple, but the active light emitting area is minimized for a given device perimeter
Solution Approach 1:
The contact layer is designed with an asymmetric shape that is specifically optimized for flip chip packaging. The contact layer includes a first contact layer region and a second contact layer region arranged in an asymmetric pattern that maximizes the active light emitting area while providing proper contact areas for flip chip mounting. This asymmetric design breaks the conventional symmetry to achieve better packaging efficiency and larger light emitting area.
3Reliability
If the distance from metal contact to LED center is reduced to decrease current crowding effect, then the current distribution improves, but the beam shape becomes impractical and packaging is difficult
Solution Approach 1:
The contact layer design transitions from a conventional planar circular contact to a multi-dimensional asymmetric structure with distinct first and second contact layer regions. This dimensional reconfiguration allows the contact layer to extend in specific directions to provide optimal current distribution while maintaining proper distances for packaging. The asymmetric arrangement in multiple spatial dimensions enables both improved current uniformity and practical packaging geometry.
Data Source
AI summary
An improved light emitting heterostructure and/or device is provided, which includes a contact layer having a contact shape comprising one of: a clover shape with at least a third order axis of symmetry or an H-shape. The use of these shapes can provide one or more improved operating characteristics for the light emitting devices. The contact shapes can be used, for example, with contact layers on nitride-based devices that emit light having a wavelength in at least one of: the blue spectrum or the deep ultraviolet (UV) spectrum.