Inverted III-V Laser Diode with Buried Tunnel Junction
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Solution Overview
Problem
Conventional III-nitride laser diodes grown on (0001) Ga-polar substrates face issues with detrimental band alignment and optical losses due to high resistivity p-type layers, leading to decreased injection efficiency and increased optical losses.
Innovation Solution
The use of tunnel junctions to invert the relative arrangement of built-in polarization and current flow direction in metal (III)-polar grown III-nitride laser diodes, placing the tunnel junction below the active region, which eliminates the need for an electron blocking layer and enhances band alignment, thereby improving injection efficiency and reducing optical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional p-type layers are used in III-nitride laser diodes, then current injection is enabled, but high resistivity causes detrimental band alignment and decreased injection efficiency
Solution Approach 1:
The patent inverts the conventional layer sequence by placing p-type layers at the bottom instead of the top, and uses a buried tunnel junction to inject carriers from the p-type side. This inversion allows the p-type layers to be positioned where they do not cause optical losses while still enabling current injection through the tunnel junction mechanism.
Solution Approach 2:
The buried tunnel junction acts as an intermediary structure that enables efficient carrier injection from the p-type layers into the active region. The tunnel junction provides a low-resistance path for hole injection, mediating between the p-type contact and the active region to achieve high injection efficiency without requiring thick high-resistivity p-type layers.
2Reliability
If Mg-doped electron blocking layer is placed near the active region, then injection efficiency is improved, but optical losses increase due to the doped layer
Solution Approach 1:
The patent extracts the electron blocking function from a separate Mg-doped layer and integrates it into the tunnel junction structure itself. The tunnel junction inherently provides electron blocking while maintaining low optical losses, eliminating the need for a separate doped electron blocking layer that would cause optical absorption.
Solution Approach 2:
The patent merges the electron blocking function with the tunnel junction structure, combining multiple functions (carrier injection, electron blocking, and low optical loss) into a single integrated structure. This merging eliminates the need for separate doped layers and reduces overall optical losses.
3Ease of operation
If thick p-type layers are used, then current injection is facilitated, but resistivity increases causing detrimental band alignment
Solution Approach 1:
The patent inverts the conventional approach by using a thin highly-doped p-type layer combined with a buried tunnel junction instead of thick moderate-doped p-type layers. This inversion enables efficient current injection through the tunnel junction while maintaining proper band alignment by minimizing the thickness and optimizing the doping of the p-type layer.
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 configuration achieves 100% injection efficiency and reduces light absorption, enabling higher current spreading and enhanced light confinement, resulting in improved light output power, such as a 30% enhancement compared to standard top-TJ devices.
Implementation Method 1
The present technology is based on the use of tunnel junctions (TJs) to invert relative arrangement of the built-in polarization and current flow direction
Data Source
AI summary
Tunnel junctions (TJs) are used to invert a relative arrangement of the built-in polarization and current flow direction for metal (Ill)-polar grown Ill-nitride laser diodes (LDs). The resulting devices has subsequent TJ, p-type layers, active region and n-type layers. This arrangement ensures a band alignment which provides an injection efficiency of 100% without the need of close proximity of an electron blocking layer.