Nonpolar GaN Substrate Cleavage for Laser Diode Mirror Surfaces
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Solution Overview
Problem
The formation of a high-quality cleavage surface in nitride-based semiconductor laser diodes is challenging due to the mismatch between the sapphire substrate and the GaN-based epitaxial layer, leading to increased roughness and reduced light emission efficiency, especially when using heterogeneous substrates and polar c-plane GaN substrates that generate adverse built-in electric fields.
Innovation Solution
A method involving the use of a-plane or m-plane GaN substrates with no polarity, where wet etching is applied to form a crystallographic surface, using KOH as the etching liquid, to create a mirror surface that coincides with the crystal surface, thereby reducing roughness and eliminating built-in electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a heterogeneous substrate (sapphire) is used for GaN-based epitaxial layer, then cost and availability are improved, but the crystal surface mismatch causes increased roughness of the cleavage surface
Solution Approach 1:
The invention changes the substrate crystal orientation parameter from conventional c-plane to a-plane or m-plane GaN substrates. This parameter change eliminates the 30-degree crystal surface mismatch between sapphire substrate and GaN epitaxial layer, enabling the formation of smooth cleavage surfaces that coincide with the crystal surface, thereby resolving the roughness issue while maintaining substrate availability
Solution Approach 2:
The invention uses a template approach where the crystal structure of the GaN epitaxial layer is copied onto the substrate by selecting a substrate with matching crystal orientation (a-plane or m-plane). This ensures that the cleavage surface naturally follows the crystal surface without deviation, eliminating the need for complex post-processing to achieve smooth surfaces
2Manufacturing precision
If notching and cleaving process is applied to form mirror surface on heterogeneous substrate, then mirror surface formation is achieved, but the cleavage surface eats into patterns reducing yield
Solution Approach 1:
By changing the substrate orientation parameter to a-plane or m-plane GaN substrates, the invention enables the cleavage surface to naturally coincide with the crystal surface. This eliminates the need for aggressive notching and cleaving processes that cause pattern damage, thereby maintaining high device yield while achieving high-quality mirror surfaces
Solution Approach 2:
The invention performs preliminary action by selecting the appropriate substrate crystal orientation (a-plane or m-plane) before epitaxial growth. This preliminary selection ensures that the subsequent cleavage process will produce smooth surfaces that follow the crystal structure, preventing the need for corrective measures that could damage device patterns
3Ease of manufacture
If c-plane GaN substrate is used, then conventional manufacturing is maintained, but built-in electric fields from polarization reduce light emission efficiency
Solution Approach 1:
The invention changes the fundamental parameter of substrate crystal orientation from c-plane (polar) to a-plane or m-plane (non-polar). This parameter change eliminates the polarization-induced built-in electric fields that cause carrier separation and reduce light emission efficiency, while still maintaining compatibility with GaN-based semiconductor manufacturing processes
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 light emission efficiency by aligning semiconductor laser diode structures with the crystal direction, reducing operational current and improving yield by forming a high-quality cleavage surface that matches the crystallographic orientation, thus preventing red shift emission and increasing light extraction efficiency.
Implementation Method 1
applying the masked GaN substrate to etching liquid, thereby forming a crystallographic surface
Implementation Method 2
wet etching is applied to form a crystallographic surface, using KOH as the etching liquid
Implementation Method 3
the c-plane of GaN crystal is known as a polar plane. Therefore, built-in electric fields generated by the polarization of the c-plane may have an adverse effect upon the combination of electrons and holes
Data Source
AI summary
Provided is a method of manufacturing a semiconductor laser diode. The method includes the steps of: preparing a GaN substrate having an a-plane or m-plane GaN layer formed thereon; forming a plurality of laser diode structures on the GaN layer; etching the GaN substrate such that a cutting reference line is formed in a groove shape along the crystal surface of the a-plane or m-plane, not a main plane; and cutting the GaN substrate along the cutting reference line so as to form a mirror surface of the semiconductor laser diode, the mirror surface coinciding with the crystal surface of the a-plane or m-plane, not the main plane.