Nitride Semiconductor Mesa Structure Current Concentration
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Solution Overview
Problem
The luminescence efficiency of group III nitride semiconductor luminescence elements with a mesa structure is decreased due to current concentration near the edge of the mesa structure, leading to uneven luminescence, particularly for deep ultraviolet ray emitting elements with high Al composition in the n-type layer.
Innovation Solution
A p-electrode structure comprising a first metal layer, a conductive layer with higher specific resistance, and a second metal layer is laminated on the p-type layer, with the conductive layer's thickness ranging from 0.05 µm to 20 µm and specific resistance between 0.1 x 10^-4 to 1.0 x 10^-2 Ωcm, and the distance between the mesa edge and the outer peripheral of the second metal layer being 1/3 to 1.2 times the current spreading length or 20 µm to 40 µm, to suppress current concentration at the mesa edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a mesa structure is formed in the luminescence element, then the device complexity is reduced and ease of manufacture is improved, but current concentration occurs at the mesa edge causing luminescence efficiency to decrease
Solution Approach 1:
The patent applies local quality by creating a high resistance layer specifically at the mesa edge region where current concentration occurs. This localized modification of electrical resistance properties prevents current from concentrating at the problematic edge area, thereby maintaining luminescence efficiency while preserving the overall mesa structure's manufacturing advantages
Solution Approach 2:
The high resistance layer acts as an intermediary element between the p-type layer and the mesa edge. It mediates the current flow by providing a controlled resistance path that prevents direct current concentration at the mesa edge, thus protecting the luminescence efficiency without requiring fundamental changes to the device structure
2Reliability
If a high resistance layer is formed on the p-type layer close to the mesa edge, then current concentration is suppressed, but the production steps increase and device complexity increases
Solution Approach 1:
The patent merges the high resistance layer formation with the existing p-type layer processing steps. By integrating the resistance modification into the existing fabrication sequence rather than adding completely separate processing stages, the device complexity increase is minimized while still achieving the desired current suppression effect
3Reliability
If a trench is formed between the p-electrode and n-electrode to suppress current concentration, then current pathway length variation is reduced, but the production steps increase and manufacturing becomes more complicated
Solution Approach 1:
Instead of forming a physical trench structure that would require additional fabrication steps, the patent extracts the current control function and implements it through a high resistance layer. This approach achieves the same current distribution improvement without the manufacturing complexity of trench formation
4Illumination intensity
If the n-type layer has high Al composition for deep ultraviolet emission, then the luminescence peak wavelength is in the 200-350 nm range, but the specific resistance increases causing current concentration at the mesa edge
Solution Approach 1:
The high resistance layer serves as an intermediary that compensates for the high specific resistance of the Al-rich n-type layer. It provides an additional control mechanism for current flow that overrides the inherent current concentration tendency caused by the high resistance of the deep ultraviolet emitting 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
The solution ensures uniform current distribution to the active layer, reducing uneven luminescence and maintaining luminescence efficiency, especially for ultraviolet ray emitting elements with a peak wavelength of 200 to 350 nm, by preventing current concentration at the mesa edge, thus enhancing the overall performance and reducing driving voltage.
Implementation Method 1
a p-electrode structure (30) comprising a first metal layer (18), a conductive layer (19) and a second metal layer (20) which are laminated in this order on the p-type layer (14), and a specific resistance of the conductive layer (19) is higher than a specific resistance of the first metal layer (18)
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
[Problem] To provide a technique for suppressing decrease of the luminous efficiency of a semiconductor element having a mesa structure by suppressing concentration of electric current flowing between a p electrode and an n electrode in a region near the mesa end. [Solution] A group III nitride semiconductor element which comprises an active layer between an n-type layer and a p-type layer and has a mesa structure containing the p-type layer, and which comprises an n electrode on the n-type layer and a p electrode on the p-type layer, said p electrode being obtained by sequentially laminating a first metal layer, a conductive layer and a second metal layer in this order. The resistivity of the conductive layer is higher than the resistivity of the first metal layer.