Group III Nitride Semiconductor Laser With Superlattice Cladding
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Solution Overview
Problem
High-output Group III nitride semiconductor lasers face challenges in achieving stable high current injection efficiency due to variations in film deposition conditions and the introduction of dislocations when using a cladding layer with a superlattice structure, leading to issues such as device splitting during manufacturing and reduced current injection efficiency.
Innovation Solution
The semiconductor laser design incorporates a cladding layer with a superlattice structure where the dislocation density is higher above the current-confining layer than above the current injection region, and a current-confining layer with a high-aluminum composition, combined with a pair of stripe-shaped current-confining layers to reduce strains and dislocations, thereby improving current injection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cladding layer with a superlattice structure is used to reduce resistance and improve carrier mobility, then operating voltage decreases and current injection efficiency improves, but dislocations are introduced during film deposition causing current injection efficiency to become unstable and device splitting during manufacturing
Solution Approach 1:
An undoped GaN layer is introduced as an intermediary between the current-confining layer and the cladding layer. This intermediate layer acts as a buffer that reduces the direct interaction between the high-strain current-confining layer and the cladding layer, thereby suppressing dislocation propagation while maintaining the beneficial electrical properties of the superlattice cladding structure
Solution Approach 2:
The doping is extracted from the GaN layer adjacent to the current-confining layer, creating an undoped region. This removal of dopants eliminates the additional strains and dislocations that would otherwise be generated by doped regions, allowing the superlattice cladding to function without being compromised by defect propagation from heavily doped adjacent layers
2Reliability
If the ridge width is narrowed to control transverse mode for Gaussian intensity profile, then beam focusing efficiency improves, but electrode area decreases resulting in increased contact resistance and heat generation
Solution Approach 1:
The current-confining function is segmented from the transverse mode control function. The current-confining layer (AlN or (Al)GaN) is specifically designed to confine current vertically, while the ridge geometry and cladding layers handle transverse mode control. This segmentation allows the electrode width to be wider for lower contact resistance while the optical mode is still properly confined through the current-confining layer structure
Solution Approach 2:
The invention transitions from controlling current confinement purely through horizontal ridge geometry to using vertical current-confining layers. By introducing the current-confining layer dimension, the system can maintain effective current confinement with wider electrodes, reducing contact resistance while preserving beam quality through the vertical confinement mechanism
3Object-affected harmful factors
If AlN or (Al)GaN is used to form the current-confining layer for wide contact area, then contact resistance decreases, but device splitting occurs during isolation, wire bonding, and soldering due to lattice constant differences
Solution Approach 1:
The undoped GaN layer is placed beforehand between the current-confining layer and the cladding layer to cushion against dislocation propagation. This buffer layer is positioned in advance to prevent the transmission of mechanical stresses and lattice mismatches from the AlN or (Al)GaN current-confining layer to the overlying structures, thereby preventing device splitting during subsequent 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 design stabilizes current injection efficiency, reduces operating voltage, and enhances the reliability of the semiconductor laser by minimizing dislocations and strains, resulting in improved performance and reduced threshold current.
Implementation Method 1
Because a carrier is induced to the interface of each layer composing the superlattice structure, the resistance in the thickness-direction of the layers decreases, and the carrier mobility in the in-plane direction of the layers increases
Implementation Method 2
the dislocation density of the cladding layer in a region directly above the current-confining layer is higher than the dislocation density of the cladding layer in a region directly above the opening for current injection
Data Source
AI summary
The present invention provides a semiconductor laser excellent in the current injection efficiency. In an inner stripe type semiconductor laser according to the present invention, a p type cladding layer 309 has a superlattice structure composed of GaN layers and Al0.1Ga0.9N layers, which are alternately layered on each other. The p type cladding layer 309 has a portion of high dislocation density and a portion of low dislocation density. That is, the dislocation density is relatively low in a region directly above an opening of the current-confining region 308, whereas the dislocation density is relatively high in a region directly above a current-confining region 308.