Semipolar GaN LED Structure for Efficiency Droop Reduction
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Solution Overview
Problem
Current LEDs experience efficiency droop at high driving currents, leading to increased wafer area and cost requirements for high-power applications, limiting their adoption in commercial lighting, particularly in automotive and illumination sectors.
Innovation Solution
A low-droop light emitting diode (LED) structure is developed using (Al,Ga,In)N thin films grown on a GaN semipolar {20-2-1} substrate with an n-type superlattice below and a p-type superlattice above the quantum well active region, fabricated via metal organic chemical vapor deposition (MOCVD), which reduces efficiency droop to 15% or less at current densities of 35 A/cm2 and maintains high light output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional LED structures are used, then high brightness can be achieved, but efficiency droop increases at high driving currents
Solution Approach 1:
The patent changes the crystal orientation parameter from conventional polar c-plane to semipolar {20-2-1} plane, and modifies the active region structure by introducing gradient-composition InGaN quantum wells with varying indium content. These parameter changes reduce efficiency droop while maintaining high brightness at elevated current densities
Solution Approach 2:
The patent employs composite material structures including InGaN/GaN quantum well superlattices with gradient indium composition, combined with AlGaN electron blocking layers and specific doping configurations. This composite approach optimizes carrier confinement and reduces Auger recombination, addressing efficiency droop
2Power
If higher driving current is used to increase power output, then light output power increases, but efficiency droop worsens
Solution Approach 1:
By changing the crystal plane to semipolar {20-2-1} and implementing gradient-composition quantum wells, the patent enables the LED to maintain higher external quantum efficiency at elevated current densities, allowing increased power output with reduced efficiency loss
Solution Approach 2:
The patent implements preliminary strain management through careful layer thickness control and composition grading in the quantum well structure, which pre-configures the device to handle high current densities more effectively, reducing efficiency droop before it occurs during operation
3Power
If larger wafer area is used to compensate for efficiency droop, then high power application requirements are met, but manufacturing cost increases
Solution Approach 1:
The semipolar {20-2-1} crystal orientation and gradient-composition quantum well structure improve power density per unit area, allowing high power output from smaller wafer areas, thereby reducing manufacturing costs while meeting high power application requirements
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 effectively minimizes efficiency droop, enabling LEDs to operate efficiently at high current densities with reduced power loss, thus enhancing their suitability for widespread adoption in high-power applications like automotive lighting and general illumination.
Implementation Method 1
an n-type superlattice (n-SL) or n-SL layers located below the QW active region, and p-type superlattice (p-SL) or p-SL layers above the QW active region
Implementation Method 2
a quantum well (QW) active region of two or more periods
Data Source
AI summary
A light emitting diode structure of (Al,Ga,In)N thin films grown on a gallium nitride (GaN) semipolar substrate by metal organic chemical vapor deposition (MOCVD) that exhibits reduced droop. The device structure includes a quantum well (QW) active region of two or more periods, n-type superlattice layers (n-SLs) located below the QW active region, and p-type superlattice layers (p-SLs) above the QW active region. The present invention also encompasses a method of fabricating such a device.