GaN Light Emitting Device Laser Separation via AlGaN Buffer
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Solution Overview
Problem
Current methods for manufacturing GaN-based semiconductor light emitting devices on sapphire substrates face efficiency losses due to light reflection, heat damage, and high-density threading dislocations, particularly in the ultraviolet region, where crystal defects significantly impact performance.
Innovation Solution
A method involving the formation of a crystalline AlxGa1−xN buffer layer on a c-plane sapphire substrate, followed by a GaN layer, and subsequent separation using a laser with a wavelength shorter than the GaN bandgap, which reduces crystal damage and enhances thermal conductivity, thereby improving efficiency and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high-power laser is used to decompose the GaN layer for substrate separation, then substrate separation is achieved, but heat and stress damage the device structure unit causing efficiency decrease and threading dislocations
Solution Approach 1:
The patent introduces a buffer layer as an intermediary substance between the sapphire substrate and the GaN layer. This buffer layer absorbs the harmful heat and stress from laser irradiation, preventing direct damage to the device structure while still allowing the laser to decompose the GaN layer for substrate separation. The buffer layer acts as a mediator that protects the sensitive device components from the harsh separation process.
Solution Approach 2:
The buffer layer is formed in advance before the device structure is completed and before laser separation is performed. This preliminary action ensures that the protective layer is already in place to shield the device from heat and stress damage during the subsequent substrate separation process, rather than attempting to protect the device after damage has occurred.
2Productivity
If laser irradiation is applied from the substrate side to decompose GaN, then substrate separation is achieved, but cracks occur due to residual strain reducing yield
Solution Approach 1:
The buffer layer serves as a mediator that absorbs residual strain and prevents crack propagation during laser-induced substrate separation. By positioning the buffer layer between the substrate and the device, it cushions the mechanical stress and prevents cracks from forming in the device structure, thereby maintaining high yield.
3Ease of manufacture
If GaN-based mixed crystal is grown on sapphire substrate via low-temperature amorphous layer or polycrystal buffer layer, then growth is achieved, but nearly half of emitted light is reflected due to refractive index difference
Solution Approach 1:
The patent changes the temperature parameter during buffer layer formation, using high-temperature growth to create a crystalline buffer layer instead of a low-temperature amorphous layer. This parameter change modifies the optical properties of the buffer layer, reducing light reflection and improving light extraction efficiency while maintaining the feasibility of growing GaN-based mixed crystal on sapphire substrate.
Solution Approach 2:
The patent creates a composite structure consisting of the sapphire substrate, crystalline buffer layer, and GaN-based mixed crystal layer. This composite material approach allows optimization of each layer's properties: the sapphire provides mechanical support, the crystalline buffer layer provides both structural support and improved optical transmission, and the GaN layer provides light emission. The composite structure reduces overall light reflection compared to simple amorphous buffer layers.
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 the productivity and efficiency of semiconductor light emitting devices by minimizing crystal damage, reducing defects, and increasing yield, especially for ultraviolet wavelengths, by using a high-thermal-conductivity buffer layer to manage heat and stress during laser separation.
Implementation Method 1
irradiating a laser beam which is absorbed in the first semiconductor layer to decompose the first semiconductor layer
Implementation Method 2
irradiating the GaN layer with a laser having a wavelength shorter than a bandgap wavelength of GaN from the first substrate side through the first substrate and the buffer layer
Implementation Method 3
forming a buffer layer made of a crystalline AlxGa1−xN (0.8≦x≦1) on a first substrate made of c-plane sapphire and forming a GaN layer on the buffer layer
Data Source
AI summary
A method for manufacturing a semiconductor light emitting device is provided. The device includes: an n-type semiconductor layer; a p-type semiconductor layer; and a light emitting unit provided between the n-type semiconductor layer and the p-type semiconductor layer. The method includes: forming a buffer layer made of a crystalline AlxGa1−xN (0.8≦x≦1) on a first substrate made of c-plane sapphire and forming a GaN layer on the buffer layer; stacking the n-type semiconductor layer, the light emitting unit, and the p-type semiconductor layer on the GaN layer; and separating the first substrate by irradiating the GaN layer with a laser having a wavelength shorter than a bandgap wavelength of GaN from the first substrate side through the first substrate and the buffer layer.