Graded AlGaN LED Layer for UV Light Extraction
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Solution Overview
Problem
High aluminum content in p-type doped III-nitride materials used in light emitting diodes (LEDs) leads to poor hole transport properties and increased device voltages, limiting the efficiency of ultraviolet (UV) LEDs, as they become optically absorbing at emission wavelengths, necessitating the use of low aluminum materials that sacrifice emitted light for lower operating voltages.
Innovation Solution
A transparent graded electron blocking and hole transporting layer (TEBHTL) is implemented, composed of compositionally graded III-nitride materials like AlGaN, which utilizes polarization enhanced doping to achieve high hole concentrations and block electrons, while being optically transparent to enable efficient light extraction through a composite electrical contact layer with a reflective metal component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high aluminum content p-type doped III-nitride materials are used, then hole concentration can be increased, but hole transport properties deteriorate and device voltage increases
Solution Approach 1:
The patent applies local quality by creating a compositionally graded AlGaN layer where the aluminum content varies spatially - higher aluminum content near the active region for hole generation, and lower aluminum content toward the contact for optimal hole transport. This gradient structure allows different regions to have optimized properties for their specific functions.
Solution Approach 2:
The patent utilizes parameter changes by continuously varying the aluminum composition parameter throughout the p-type layer. The composition gradient transforms the material properties gradually, enabling high hole concentration near the active region while maintaining good hole transport properties toward the contact, thus resolving the contradiction between hole concentration and transport properties.
2Power
If high aluminum containing materials are used on the p-side, then device voltage can be reduced, but optical transparency deteriorates due to light absorption
Solution Approach 1:
The compositionally graded AlGaN layer implements local quality by having different aluminum compositions at different positions. The region closer to the active region has higher aluminum content for voltage control, while the region closer to the contact has lower aluminum content for optical transparency, allowing both functions to be optimized simultaneously.
Solution Approach 2:
The patent resolves the contradiction by adding a compositional gradient dimension to the p-type layer. Instead of using a uniform material, the aluminum composition varies along the depth direction, creating a three-dimensional material structure where both high voltage control and optical transparency can be achieved in different spatial regions.
3Object-generated harmful factors
If low aluminum containing materials are used on the p-side, then optical transparency is improved, but device voltage increases to very high values
Solution Approach 1:
The graded AlGaN structure applies local quality by positioning low aluminum content regions where optical transparency is critical (near the contact) and high aluminum content regions where voltage control is critical (near the active region). This spatial differentiation resolves the contradiction between transparency and voltage control.
Solution Approach 2:
The patent uses parameter changes in the aluminum composition to simultaneously achieve optical transparency and voltage control. By gradually changing the composition parameter through the layer thickness, the material can provide both low absorption in transparent regions and appropriate band structure for voltage control in other regions.
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 TEBHTL enhances carrier injection efficiency, reduces device voltage, and improves light extraction by redirecting p-side going light back into the device, increasing overall output power while maintaining high hole conductivity and optical transparency.
Implementation Method 1
The composition grading in the TEBHTL produces a built-in polarization field that helps to ionize p-dopants to produce high hole concentration.
Implementation Method 2
The composite electrical contact layer with a reflective metal component... improving light extraction by redirecting p-side going light back into the device
Data Source
Figure 1
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Figure 3A
AI summary
A light emitting diode includes an active region configured to emit light, a composite electrical contact layer, and a transparent electron blocking hole transport layer (TEBHTL). The composite electrical contact layer includes tow materials. At least one of the two materials is a metal configured to reflect a portion of the emitted light. The TEBHTL is arranged between the composite electrical contact layer and the active region. The TEBHTL has a thickness that extends at least a majority of a distance between the active region and the composite electrical contact layer. The TEBHTL has a band-gap greater than a band-gap of light emitting portions of the active region. The band-gap of the TEBHTL decreases as a function of distance from the active region to the composite electrical contact layer over a majority of the thickness of the TEBHTL.