GaN Light Emitting Package Tensile Stress Thermal Droop
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Solution Overview
Problem
Light emitting devices experience thermal droop, leading to reduced luminous efficiency as temperature increases, due to non-radiative electron-hole recombination, and existing solutions have not thoroughly addressed this issue.
Innovation Solution
A light emitting package design incorporating a sequential stack of semiconductor layers with an encapsulation layer and a wavelength conversion layer having a higher coefficient of thermal expansion (CTE) than GaN, applied tensile stress to the light emitting stack, and optimized optical reflectance to reduce thermal droop and enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the temperature of the light emitting device increases, then the operation temperature range is extended, but thermal droop occurs and luminous efficiency deteriorates
Solution Approach 1:
The patent applies thermal expansion by selecting encapsulation and wavelength conversion layer materials with a coefficient of thermal expansion (CTE) greater than that of the GaN light emitting stack. This CTE mismatch generates tensile stress on the stack during temperature increases, which suppresses non-radiative recombination and reduces thermal droop, thereby maintaining luminous efficiency at elevated temperatures.
2Loss of energy
If tensile stress is applied to the light emitting stack, then thermal droop is reduced and luminous efficiency is improved, but device structure becomes more complex
Solution Approach 1:
The patent employs self-service by allowing the encapsulation and wavelength conversion layers to automatically generate the required tensile stress through their inherent thermal expansion properties when temperature increases. This eliminates the need for external stress application mechanisms or complex stress control systems, maintaining structural simplicity while achieving thermal droop reduction.
3Loss of energy
If materials with higher CTE than GaN are used for encapsulation and wavelength conversion layers, then thermal droop is reduced, but material selection becomes more restricted
Solution Approach 1:
The patent applies parameter changes by specifying a CTE range (greater than GaN's CTE) for the encapsulation and wavelength conversion layer materials rather than requiring an exact match. This parameter-based approach provides design flexibility, allowing engineers to select from multiple material options that satisfy the CTE requirement while considering other factors such as optical properties, chemical compatibility, and manufacturing considerations.
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 reduces thermal droop and improves luminous efficiency by applying tensile stress through the encapsulation and wavelength conversion layers, maintaining efficiency across a temperature range of 25°C to 85°C with a luminous flux deterioration rate less than -5%.
Implementation Method 1
At least one of the encapsulation layer and the wavelength conversion layer may have a greater coefficient of thermal expansion (CTE) than a compound semiconductor of AlxInyGazN
Implementation Method 2
A light emitting device generates light based on emission of electromagnetic waves due to recombination of electrons and holes
Implementation Method 3
An optical reflectance of the encapsulation layer may be about 80% to about 100%
Data Source
AI summary
A semiconductor light emitting device may include a light emitting package. A light emitting package may include a light emitting stack including a sequential stack of a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. An encapsulation layer may at least partially surround the second conductivity type semiconductor layer, and a wavelength conversion layer may cover the first conductivity type semiconductor layer. One or more of the encapsulation layer and the wavelength conversion layer may have a greater coefficient of thermal expansion (CTE) than a GaN-based compound semiconductor. The semiconductor light emitting device may include a stress applying structure that may apply a tensile stress to the light emitting stack. The light emitting stack may have reduced thermal droop at an operation temperature and improved luminous efficiency.