Vertical GaN LED with Polarity-Engineered Recovery Layer
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Solution Overview
Problem
The existing vertical-structure chip technology faces instability in n-surface GaN ohmic contact electrodes, leading to poor voltage reliability due to the difficulty in forming stable ohmic contacts with nitride polarity surfaces, which affects the performance of GaN-based LED chips.
Innovation Solution
A vertical LED epitaxial structure is designed with a nitrided substrate, an n-type nitride layer having alternating nitride and gallium polarity crystals, an n-type recovery layer, an active layer, and a p-type layer, where the n-type nitride layer's surface is predominantly gallium polarity, enabling the use of mature Ti/Al metal electrodes for stable ohmic contact after substrate lift-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional Ti/Al metal electrodes are used on nitride polarity GaN surfaces, then the manufacturing process is simple, but the ohmic contact stability is poor
Solution Approach 1:
The patent applies local quality by creating a recovery layer with gallium polarity surface in specific regions where ohmic contact is needed. The n-type recovery layer is grown to expose gallium polarity surfaces locally, allowing conventional Ti/Al electrodes to form stable ohmic contacts only in those specific areas, while other regions maintain their original nitride polarity characteristics.
Solution Approach 2:
The n-type recovery layer acts as an intermediary between the nitride polarity GaN layer and the metal electrode. This intermediate layer with gallium polarity surface enables conventional Ti/Al electrodes to form stable ohmic contacts by providing the appropriate surface polarity, thus mediating the interaction between the electrode and the underlying nitride polarity GaN.
2Ease of manufacture
If the n-type nitride layer is grown with mixed polarity, then the crystal growth is facilitated, but the surface polarity uniformity is poor
Solution Approach 1:
The patent segments the n-type nitride layer into different polarity regions by controlling the substrate nitridation pattern. The nitrided regions promote nitride polarity crystal growth while non-nitrided regions promote gallium polarity crystal growth, creating a segmented structure with alternating polarity domains that facilitates overall crystal growth while providing distinct surface polarity areas.
Solution Approach 2:
The patent applies local quality by creating specific regions with different polarities within the n-type nitride layer. By controlling the substrate nitridation pattern (periodically-arranged band-shaped or block-shaped), different areas of the layer develop different surface polarities, allowing the structure to have both facilitation of crystal growth and controlled polarity distribution.
3Stability of the object's composition
If the recovery layer thickness is increased, then the gallium polarity surface coverage is improved, but the material consumption increases
Solution Approach 1:
The patent applies partial action by growing the n-type recovery layer to a thickness that is sufficient to expose the required amount of gallium polarity surface (at least 50% coverage) but not excessively thick. This optimized thickness range (0.3-1 μm) provides just enough material to achieve the desired surface polarity coverage while minimizing unnecessary material consumption.
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 improves the voltage stability and reliability of GaN-based LED chips by ensuring stable ohmic contact on the nitride polarity surface, enhancing the light-emitting efficiency and performance of the vertical GaN chip.
Implementation Method 1
a substrate, having an upper surface and a bottom surface opposite to each other, in which, a portion of the upper surface is nitrided
Implementation Method 2
an n-type nitride layer, formed on the upper surface of the substrate having a nitride polarity crystal and a gallium polarity crystal
Data Source
AI summary
A light-emitting diode (LED) chip includes from bottom to up: a conductive substrate, a p-type nitride layer, an active layer, an n-type recovery layer, an n-type nitride layer and an n electrode, wherein, the n-type nitride layer has a nitride polarity crystal and a gallium polarity crystal, and the surfaces of the nitride polarity and the gallium polarity regions appear different in height, the n-type recovery layer surface approximate to the n-type nitride layer has consistent mixed polarity with the n-type nitride layer, and the surface far from the n-type nitride layer is a connected gallium polarity surface.