Graded P-Type Semiconductor Layer for LED Voltage Reduction
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Solution Overview
Problem
Semiconductor light emitting devices face challenges in enhancing crystallinity, reducing nonradiative recombination centers, improving internal quantum efficiency, and increasing hole injection efficiency, while also requiring lower operating voltages.
Innovation Solution
The semiconductor light emitting device incorporates a p-type semiconductor layer with a specific graded impurity concentration profile, including a first p-type layer with a high Mg concentration, a second p-type layer with a moderate Mg concentration, a third p-type layer with a lower Mg concentration, and a fourth p-type layer with a decreasing Mg concentration, along with a multiple quantum well structure, to enhance hole injection efficiency and reduce operating voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a p-type semiconductor layer with conventional uniform impurity concentration is used, then the device structure is simple, but the hole injection efficiency is low and operating voltage is high
Solution Approach 1:
The p-type semiconductor layer is divided into multiple regions with different impurity concentrations: a first region with higher Mg concentration and a second region with lower Mg concentration. This local differentiation optimizes hole injection efficiency in each region while maintaining overall device functionality, resolving the contradiction between structural simplicity and injection efficiency.
Solution Approach 2:
The impurity concentration parameter is varied spatially within the p-type semiconductor layer, transitioning from a uniform concentration to a graded or multi-level concentration profile. This parameter change enables improved hole injection efficiency and reduced operating voltage while maintaining manufacturing feasibility.
2Reliability
If the p-type impurity concentration is increased to improve hole injection, then the hole density increases, but the crystallinity deteriorates and nonradiative recombination centers increase
Solution Approach 1:
Different regions of the p-type semiconductor layer are assigned different impurity concentrations: the first region has higher Mg concentration for improved hole injection, while the second region has lower Mg concentration to maintain crystallinity and reduce nonradiative recombination centers. This spatial differentiation resolves the contradiction between injection efficiency and crystal quality.
Solution Approach 2:
The Mg impurity concentration is optimized to specific ranges: the first region contains Mg at 1×10^19 to 1×10^20 atoms/cm³, while the second region contains Mg at 1×10^18 to 1×10^19 atoms/cm³. This parameter optimization achieves both improved hole injection and maintained crystallinity.
3Device complexity
If a single-layer p-type structure is used, then the device complexity is low, but the series resistance is high and operating voltage cannot be reduced
Solution Approach 1:
The p-type semiconductor layer is segmented into multiple distinct regions with different impurity concentrations rather than using a uniform single-layer structure. This segmentation reduces series resistance by creating optimized conduction paths while maintaining reasonable device complexity through a systematic multi-region architecture.
Solution Approach 2:
The spatial variation of Mg concentration parameters across different regions of the p-type layer optimizes electrical conductivity and reduces series resistance. The graded or multi-level concentration profile enables better charge carrier transport compared to uniform doping, thereby reducing energy loss.
Data Source
AI summary
According to one embodiment, a semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, a light emitting part, and a p-side electrode. The light emitting part is provided between the n-type and the p-type semiconductor layers, and includes a plurality of barrier layers and a plurality of well layers. The p-side electrode contacts the p-type semiconductor layer. The p-type semiconductor layer includes first, second, third, and fourth p-type layers. The first p-type layer contacts the p-side electrode. The second p-type layer contacts the light emitting part. The third p-type layer is provided between the first p-type layer and the second p-type layer. The fourth p-type layer is provided between the second p-type layer and the third p-type layer. The second p-type layer contains Al and contains a p-type impurity in a lower concentration lower than that in the first concentration.