UV Light Emitting Mesa Layout for Reduced Current Crowding
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Solution Overview
Problem
Flip-chip type UV light emitting devices experience current crowding due to low electrical conductivity in n-type semiconductor layers, leading to insufficient light emission and reliability issues, necessitating increased forward voltage and improved current spreading.
Innovation Solution
A UV light emitting device design featuring a substrate with a mesa structure having indentations, a passivation layer with openings, and bump electrodes that cover the passivation layer and partially overlap the mesa, allowing for uniform current distribution and reduced resistance, thereby preventing current crowding and enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If electric current flows through the n-type semiconductor layer in a flip-chip type UV light emitting device, then light emission is produced, but current crowding occurs along paths with low electrical resistance leading to insufficient light emission and reliability deterioration
Solution Approach 1:
The patent divides the contact electrode into multiple segments (first contact electrode and second contact electrode) positioned at different locations on the n-type semiconductor layer. This segmentation distributes the current entry points across multiple locations, preventing current crowding at single points and promoting more uniform current distribution through the semiconductor layer, thereby improving both light emission uniformity and device reliability
Solution Approach 2:
The patent applies different properties to different regions by positioning contact electrodes at specific locations with optimized dimensions. The first contact electrode has a first dimension and the second contact electrode has a second dimension, creating local variations in current distribution patterns that collectively achieve uniform overall current spreading across the active layer
2Illumination intensity
If the n-type semiconductor layer is used for UV light emission, then UV light can be emitted, but the low electrical conductivity causes current crowding and requires increased forward voltage
Solution Approach 1:
By segmenting the contact electrode structure into multiple distributed contact regions, the patent reduces the electrical resistance pathways that current must traverse. This segmentation creates multiple parallel current paths through the n-type semiconductor layer, reducing overall resistance and forward voltage requirements while maintaining UV light emission capability
Solution Approach 2:
The patent transitions from a single-point or single-line current injection approach to a distributed two-dimensional array of contact electrodes. This dimensional change spreads current injection across multiple locations and areas, reducing current density at any single point and lowering the overall forward voltage required to achieve the same total light output
3Illumination intensity
If current flows through the semiconductor layers, then light emission occurs, but current crowding along low resistance paths results in insufficient light emission over the entire active layer region
Solution Approach 1:
The patent segments the current injection system into multiple distributed contact electrodes positioned across the n-type semiconductor layer. This segmentation ensures that current enters the semiconductor at multiple locations simultaneously, promoting uniform current distribution across the entire active layer region and achieving sufficient light emission coverage throughout the device area
Solution Approach 2:
By positioning multiple contact electrodes at appropriate locations on the n-type semiconductor layer, the patent creates equipotential regions that equalize the electrical potential distribution. This equipotentiality ensures uniform current density across the active layer, resulting in uniform light emission coverage without dark spots or insufficient emission regions
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 design effectively reduces current crowding, decreases forward voltage, and improves luminous efficiency by ensuring uniform current spreading across the semiconductor layers, leading to enhanced light emission and reliability.
Implementation Method 1
an n-type semiconductor layer used for UV light emitting devices has much lower electrical conductivity than metals. Thus, when electric current flows through the n-type semiconductor layer, an active layer, and a p-type semiconductor layer, current crowding may occur along a path having low electrical resistance
Implementation Method 2
the mesa has a plurality of indentations in plan view and each of the first bump electrode and the second bump electrode covers the openings of the passivation layer and a portion of the passivation layer... effectively reduces current crowding, decreases forward voltage, and improves luminous efficiency by ensuring uniform current spreading across the semiconductor layers
Data Source
AI summary
A light emitting device including a substrate, a first conductivity-type semiconductor layer, a mesa including a second conductivity-type semiconductor layer and an active layer, first and second contact electrodes respectively contacting the first and second conductivity-type semiconductor layers, a passivation layer covering the first and second contact electrodes, the mesa, and including first and second openings, and first and second bump electrodes electrically connected to the first and second contact electrodes through the first and second openings, respectively, in which the first and second bump electrodes are disposed on the mesa, the passivation layer is disposed between the first bump electrode and the second contact electrode, the first contact electrode includes a reflective material, and a portion of the first opening is surrounded with a side surface of the mesa, and another portion of the first opening is not surrounded with the side surface of the mesa.