GaN Substrate Separation via Selective Laser Absorption
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Solution Overview
Problem
The challenge lies in efficiently separating a GaN substrate from a GaN-based semiconductor layer without damaging the substrate, as existing methods like laser lift-off are not applicable to GaN substrates, leading to increased production costs due to non-reusability and high dislocation densities in epitaxial layers grown on heterogeneous substrates.
Innovation Solution
A method involving the preparation of a GaN substrate with a laser absorption region formed by irradiating a laser through the substrate's lower surface, allowing for the separation of the GaN substrate from the semiconductor stack without external force, and optionally using a sacrificial layer with a narrower bandgap to facilitate the separation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a heterogeneous substrate (e.g., sapphire) is used to grow GaN-based semiconductor layers, then the growth process is feasible and substrate separation is easy, but the epitaxial layer has high dislocation density due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The patent introduces a separation layer as an intermediary between the GaN substrate and the epitaxial layer. This separation layer has a bandgap narrower than GaN, allowing selective laser absorption at wavelengths that pass through GaN. The intermediary layer enables both low-dislocation-density growth (like homogeneous GaN substrate) and easy separation (like heterogeneous substrate) by providing a targeted absorption interface for laser lift-off.
Solution Approach 2:
The patent changes the optical parameter (bandgap) of the interface layer to be narrower than GaN, creating a selective absorption characteristic. This parameter change allows the same interface to serve dual purposes: maintaining crystal quality during growth and enabling selective laser absorption for separation, thus resolving the contradiction between manufacturing precision and ease of manufacture.
2Manufacturing precision
If a GaN substrate is used as a growth substrate, then the dislocation density in the epitaxial layer is reduced, but the substrate cannot be separated using conventional laser lift-off methods
Solution Approach 1:
The separation layer acts as a mediator that enables laser interaction. Since GaN itself does not absorb the laser wavelength effectively, the separation layer with narrower bandgap serves as the intermediary that absorbs the laser energy and facilitates separation, thus maintaining both the low dislocation density benefit and adding the separation capability.
Solution Approach 2:
The patent replaces the mechanical polishing method with a laser-based separation method. By introducing the separation layer with selective optical absorption properties, the separation process transitions from mechanical (polishing) to optical (laser absorption), making the process less invasive and enabling substrate reuse.
3Ease of manufacture
If conventional polishing methods are used to remove the GaN substrate, then the substrate can be removed, but the substrate cannot be reused resulting in increased production costs
Solution Approach 1:
The patent replaces mechanical polishing with optical laser absorption for substrate removal. The separation layer absorbs laser energy selectively, causing localized heating and separation at the interface without damaging the GaN substrate. This substitution enables substrate reuse, converting a destructive mechanical process into a selective optical process that preserves the valuable GaN substrate.
Solution Approach 2:
The patent converts the previously harmful effect (laser energy being entirely absorbed by GaN substrate, preventing separation) into a benefit by introducing a separation layer with narrower bandgap. This layer selectively absorbs the laser energy that previously caused damage, channeling the energy to the separation interface instead, thus enabling both separation and substrate preservation.
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
Enables the separation of the GaN substrate while maintaining high-quality semiconductor layers, allowing for the reuse of the substrate and reducing dislocation densities, thereby improving the light extraction efficiency of GaN-based LEDs with a vertical structure.
Implementation Method 1
The laser is transmitted through the lower surface of the GaN substrate and forms a laser absorption region inside a structure consisting of the GaN substrate and the semiconductor stack
Data Source
AI summary
A method of fabricating a gallium nitride (GaN)-based semiconductor device. The method includes preparing a GaN substrate having lower and upper surfaces; growing GaN-based semiconductor layers on the upper surface of the GaN substrate to form a semiconductor stack; forming a support substrate on the semiconductor stack; and separating the GaN substrate from the semiconductor stack. The separating of the GaN substrate includes irradiating a laser from the lower surface of the GaN substrate. The laser is transmitted through the lower surface of the GaN substrate and forms a laser absorption region inside a structure consisting of the GaN substrate and the semiconductor stack.