Vertical LED GaN Surface Modification for Contact Resistance
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Solution Overview
Problem
Conventional vertical LEDs with n-type GaN layers having N-face or N-polar surfaces exhibit high contact resistance and reduced thermal stability due to the sapphire substrate's poor thermal conductivity and rigid structure, leading to increased operational voltage and heating values.
Innovation Solution
The surface of the n-type GaN layer is modified to form a Ga+N layer with a higher Ga content, reducing contact resistance by increasing electron concentration, and enhancing thermal stability through laser or heat treatment, followed by the formation of an n-electrode with metals like Ti, Ta, or Zr, and creating surface irregularities for improved light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the n-electrode is positioned on the n-type GaN layer having an N-face or N-polar surface, then the LED structure is simplified, but the contact resistance of the n-electrode increases
Solution Approach 1:
The patent changes the surface orientation parameter of the n-type GaN layer from N-face or N-polar surface to C-face or C-polar surface. This parameter change fundamentally alters the surface properties, enabling the n-electrode to achieve low contact resistance while maintaining structural simplicity. The C-face/C-polar surface provides better electrical contact characteristics compared to the conventional N-face/N-polar surface.
2Ease of manufacture
If the sapphire substrate is used, then the manufacturing process is conventional, but the thermal conductivity is poor leading to increased heating value
Solution Approach 1:
The patent extracts and removes the sapphire substrate from the LED structure through laser lift-off process. By taking out the thermally problematic sapphire substrate, the invention eliminates the thermal conductivity bottleneck while preserving the ease of manufacture through established laser processing techniques. The removed substrate is replaced with a structure that allows direct heat dissipation pathways.
Solution Approach 2:
The patent transitions from a conventional planar LED structure to a vertical LED structure by changing the growth direction and electrode configuration. This dimensional reorganization creates new heat dissipation pathways in the vertical direction, improving thermal management while maintaining manufacturing feasibility through modified epitaxial growth processes.
3Power
If high current is applied to achieve high power LED, then the optical power increases, but the heat-sink problem worsens
Solution Approach 1:
The patent adopts a vertical LED structure that reorganizes the heat dissipation architecture from lateral to vertical direction. This dimensional change enables more effective heat-sink integration and creates direct thermal pathways from the active region to the heat-sink, allowing high current operation with improved thermal management capability.
Solution Approach 2:
The patent changes the surface orientation parameter to C-face or C-polar surface, which provides superior electrical and thermal contact properties. This parameter change reduces contact resistance and improves heat dissipation efficiency, enabling the LED to sustain higher operating currents and powers without excessive heating.
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 approach effectively reduces contact resistance and operational voltage, enhancing thermal stability and reliability of the vertical LED by increasing electron concentration and Schottky barrier height reduction.
Implementation Method 1
The surface of the n-type GaN layer is modified to form a Ga+N layer with a higher Ga content, reducing contact resistance by increasing electron concentration, and enhancing thermal stability through laser or heat treatment
Implementation Method 2
The surface of the n-type GaN layer is modified to form a Ga+N layer with a higher Ga content, reducing contact resistance by increasing electron concentration, and enhancing thermal stability through laser or heat treatment
Data Source
AI summary
Provided is a vertical LED including an n-electrode; an n-type GaN layer formed under the n-electrode, the n-type GaN layer having a surface coming in contact with the n-electrode, the surface having a Ga+N layer containing a larger amount of Ga than that of N; an active layer formed under the n-type GaN layer; a p-type GaN layer formed under the active layer; a p-electrode formed under the p-type GaN layer; and a structure support layer formed under the p-electrode.