UV Laser Diode Transfer Structure for Low-Absorption Cladding
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Solution Overview
Problem
The development of high-quality, high-performance ultraviolet (UV) laser diodes is hindered by excessive optical absorption due to the small bandgap of GaN, leading to internal losses and material defects, particularly in the use of native GaN substrates and foreign substrates like sapphire, which result in inefficient and fragile devices.
Innovation Solution
A method involving the growth of thin n and p-type AlGaN cladding regions and active regions on native GaN substrates, followed by transfer to a carrier wafer with transparent conductive oxide (TCO) cladding, reduces stress-induced defects and allows for the use of quaternary films, enhancing the quality and efficiency of UV laser diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If native GaN substrates are used for UV laser diode growth, then material quality and crystal structure are improved, but excessive optical absorption and internal losses occur due to small bandgap
Solution Approach 1:
The patent extracts and removes the native GaN substrate from the final device structure. A sacrificial AlN buffer layer is grown on the GaN substrate, and the substrate is selectively removed using sacrificial layer etching, leaving only the necessary thin film structure without the problematic bulk GaN material that causes optical absorption
Solution Approach 2:
The patent introduces an AlN buffer layer as an intermediary between the GaN substrate and the AlGaN cladding regions. This buffer layer serves as a transition medium that allows growth on GaN substrate while preventing the substrate's optical absorption properties from affecting the final device performance
2Loss of energy
If foreign substrates like sapphire are used, then optical absorption is reduced, but stress-induced defects and material defects increase
Solution Approach 1:
The patent uses an AlN buffer layer as an intermediary that decouples the substrate from the active device structure. This allows the use of GaN substrates without transferring their harmful optical properties to the final device, while avoiding the defect issues of foreign substrates like sapphire
Solution Approach 2:
The patent extracts the problematic substrate material from the device stack by selective removal of the GaN substrate after growing the necessary layers on it, leaving only the defect-free thin film structure
3Reliability
If thick cladding regions are grown to provide optical confinement, then optical mode confinement is improved, but dislocation and crack formation increase due to strain accumulation
Solution Approach 1:
The patent employs different Al compositions in different regions: Al-rich AlGaN cladding layers for optical confinement and GaN or InGaN active regions for light emission. This local composition variation allows thick cladding for confinement while keeping the active regions strain-free and defect-free
Solution Approach 2:
The patent uses composite AlGaN/GaN or AlGaN/InGaN heterostructure with graded compositions. The cladding regions use higher Al content for optical confinement while the active regions use lower Al content or InGaN to accommodate strain and prevent dislocation formation
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 results in high-quality AlGaN-based UV laser diodes with low loss cladding and substrate materials, improving the performance and longevity of UV laser diodes by minimizing defects and optical absorption.
Implementation Method 1
low index upper and lower transparent conductive oxide (TCO) cladding layers... providing optical confinement
Implementation Method 2
growth of thin n and p-type AlGaN cladding regions and active regions on native GaN substrates
Implementation Method 3
subjecting the release material to an energy source to initiate release of the gallium and nitrogen containing substrate member
Implementation Method 4
subjecting the release material to an energy source to initiate release of the gallium and nitrogen containing substrate member
Data Source
AI summary
An intermediate ultraviolet laser diode device includes a gallium and nitrogen containing substrate member comprising a surface region, a release material overlying the surface region, an n-type gallium and nitrogen containing material; an active region overlying the n-type gallium and nitrogen containing material; a p-type gallium and nitrogen containing material; a first transparent conductive oxide material overlying the p-type gallium and nitrogen containing material; and an interface region overlying the first transparent conductive oxide material.