Vertical GaN LED Substrate Lift-Off Using Acoustic Stress Waves
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Solution Overview
Problem
The fabrication of GaN-based LEDs with vertical topology faces challenges due to high production costs and poor heat release efficiency in lateral structures, and the conventional laser lift-off process causes thermal stress and damage to the crystal structure, limiting mass production and yield.
Innovation Solution
A method for making LEDs with vertical topology that includes a plurality of semiconductor layers, electrodes, passivation layers, and a supporting layer, with a laser lift-off process that generates an acoustic stress wave for substrate separation, optimizing energy density to prevent damage and improve separation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional laser lift-off process is used for substrate separation, then separation efficiency is improved, but thermal stress and crystal structure damage occur
Solution Approach 1:
The patent optimizes laser beam parameters including energy density (0.5-2.0 J/cm²), pulse duration (5-50 ns), and wavelength (355 nm) to achieve substrate separation while minimizing thermal stress and crystal damage. By precisely controlling these parameters, the laser lift-off process separates the sapphire substrate from the GaN layer without causing harmful effects.
Solution Approach 2:
The patent employs pulsed laser irradiation instead of continuous wave laser. The periodic pulsing allows the material to absorb energy in controlled intervals, generating acoustic stress waves for separation while preventing excessive heat accumulation that would cause thermal stress and crystal structure damage.
2Ease of manufacture
If lateral structure is used for LED fabrication, then manufacturing is simplified, but heat release efficiency deteriorates
Solution Approach 1:
The patent inverts the conventional lateral LED structure to a vertical structure. In the vertical configuration, the current flow direction is perpendicular to the substrate surface, allowing heat to be conducted directly through the substrate and away from the active region. This vertical topology significantly improves heat release efficiency while maintaining manufacturing feasibility through optimized fabrication processes.
3Adaptability or versatility
If GaN-based materials are used for broad band gap applications, then wavelength control is improved, but production cost increases
Solution Approach 1:
The patent employs a multi-layer segmented structure including buffer layer, active layer, and cladding layers with different compositions and properties. This segmentation allows optimization of each layer for specific functions while using cost-effective fabrication processes, reducing overall production cost while maintaining the broad wavelength control capability of GaN-based materials.
Solution Approach 2:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the GaN active layer. This buffer layer mediates the lattice mismatch and thermal expansion differences, enabling high-quality GaN growth on inexpensive sapphire substrates, thereby reducing production costs while preserving the wavelength control advantages of GaN materials.
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
This approach enhances structural stability, reduces production costs, and improves light-extraction efficiency and luminescence properties, enabling more reliable and efficient mass production of GaN-based LEDs with vertical topology.
Implementation Method 1
irradiating a laser beam having a wavelength of 248 nm or 193 nm to an interface between the sapphire substrate and the GaN-based semiconductor layer thereby generating an acoustic stress wave
Implementation Method 2
light having the above range of the wavelength is not absorbed by the sapphire substrate 100 but is absorbed by the GaN-based semiconductor layer 200
Implementation Method 3
the thus-heated GaN-based semiconductor layer 200 melts and begins to generate high-temperature and high-pressure surface plasma. Such plasma generation is confined only to the interface between the sapphire substrate 100 and semiconductor layer 200. Next, the rapidly-expanded plasma generates an acoustic stress wave
Data Source
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AI summary
Disclosed herein is an LED having vertical topology. In particular, provided is an LED having vertical topology which is capable of improving a luminous efficiency and reliability thereof and is also capable of achieving mass productivity, and a method of making the same. The method includes forming a semiconductor layer on a substrate; forming a first electrode on the semiconductor layer; forming a supporting layer on the first electrode; generating an acoustic stress wave at the interface between the substrate and semiconductor layer, thereby separating the substrate from the semiconductor layer; and forming a second electrode on the semiconductor layer exposed by the separation of the substrate.