UV-LED Tunable Inner Barrier Layers Reduce Efficiency Droop
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Solution Overview
Problem
LEDs, particularly UV-LEDs and visible LEDs, face efficiency droop at high injection current densities due to the Quantum Confined Stark Effect (QCSE) and carrier overflow, leading to reduced internal quantum efficiency and optical output power, with existing solutions like increasing chip size or quantum well thickness being costly or inefficient.
Innovation Solution
The introduction of tunable inner barrier (TIB) layers in the epitaxial design of LEDs, optimizing the potential energy height and thickness to enhance electron and hole wave-function overlap and carrier transport, reducing efficiency droop without using thick individual well layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the chip size is increased to reduce current density, then efficiency droop is reduced, but manufacturing cost increases
Solution Approach 1:
The patent applies local quality by creating non-uniform Al composition profiles within the quantum well layers. Specifically, the Al composition varies across the thickness of the quantum well, being lower near the electron blocking layer and higher near the p-type layer. This localized compositional variation optimizes carrier distribution and reduces efficiency droop without requiring increased chip size, thereby avoiding additional manufacturing costs.
Solution Approach 2:
The patent employs parameter changes by systematically varying the Al composition parameter across different regions of the quantum well structure. The Al mole fraction is changed from approximately 0.65-0.75 near the electron blocking layer to 0.85-0.95 near the p-type layer. This parameter optimization enables efficient carrier management and reduced efficiency droop at standard chip sizes.
2Reliability
If the quantum well thickness is increased to reduce efficiency droop, then carrier overflow is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements local quality by creating spatially varying Al composition within the quantum well thickness direction. Rather than uniformly increasing well thickness, the Al mole fraction is locally adjusted - lower (0.65-0.75) near the electron blocking layer for better electron injection, and higher (0.85-0.95) near the p-type layer for improved hole confinement. This localized optimization achieves efficiency droop reduction without increasing overall structure complexity.
Solution Approach 2:
The patent applies dynamics by creating a graded or stepped Al composition profile that dynamically adapts to the carrier distribution requirements at different positions within the quantum well. The composition gradient allows the structure to optimally manage both electron and hole carriers simultaneously, achieving reduced efficiency droop without requiring thicker or more complex multi-layer structures.
3Reliability
If the Al composition in quantum well layers is increased to reduce efficiency droop, then carrier distribution is improved, but internal quantum efficiency decreases due to QCSE
Solution Approach 1:
The patent resolves this contradiction through local quality by positioning lower Al composition (0.65-0.75) regions near the electron blocking layer where electrons are injected, and higher Al composition (0.85-0.95) regions near the p-type layer where hole confinement is critical. This spatially differentiated composition optimizes both carrier distribution for reduced efficiency droop and wave function overlap for maintained internal quantum efficiency, avoiding the QCSE penalty of uniformly high Al content.
Solution Approach 2:
The patent employs parameter changes by transitioning the Al mole fraction from 0.65-0.75 near the electron blocking layer to 0.85-0.95 near the p-type layer. This controlled parameter gradient enables the quantum well to simultaneously achieve good carrier distribution (reducing efficiency droop) and strong electron-hole wave function overlap (maintaining internal quantum efficiency), resolving the apparent contradiction between these two 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
This approach maintains high carrier concentration and reduces efficiency droop at high current injection, achieving improved external quantum efficiency and linear output power increase in UV-LEDs, enabling stable performance at higher current densities without power saturation.
Implementation Method 1
The first is the so called 'Quantum Confined Stark Effect' (QCSE), which is due to internal electric fields caused by spontaneous and piezoelectric polarization. Specifically, this internal electric field distort the MQWs and as a result the overlap of the electron and hole wave functions is reduced, leading to reduced internal quantum efficiency (IQE).
Implementation Method 2
The first is the so called 'Quantum Confined Stark Effect' (QCSE), which is due to internal electric fields caused by spontaneous and piezoelectric polarization.
Implementation Method 3
The second prominent problem is the efficiency reduction at high injection current density, which is known as 'efficiency droop'.
Data Source
AI summary
Semiconductor structures involving multiple quantum wells provide increased efficiency of UV and visible light emitting diodes (LEDs) and other emitter devices, particularly at high driving current. LEDs made with the new designs have reduced efficiency droop under high current injection and increased overall external quantum efficiency. The active region of the devices includes separation layers configured between the well layers, the one or more separation regions being configured to have a first mode to act as one or more barrier regions separating a plurality of carriers in a quantum confined mode in each of the quantum wells being provided on each side of the one or more separation layers and a second mode to cause spreading of the plurality of carriers across each of the quantum wells to increase an overlap integral of all of the plurality of carriers. The devices and methods of the invention provide improved efficiency for solid state lighting, including high efficiency ultraviolet LEDs.