GaN LED with Inclined Substrate for High-Current Thermal Management
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Solution Overview
Problem
High-power light emitting diodes (LEDs) using nitride semiconductor layers on heterogeneous substrates face limitations in current spreading and thermal management, leading to reduced luminous efficacy and increased junction temperature at high current densities, necessitating separate cooling systems.
Innovation Solution
A high-power LED design featuring a gallium nitride substrate with a first and second conductivity-type semiconductor layer, a mesa structure, and contact layers for improved current spreading, along with a gallium nitride substrate with inclined surfaces for enhanced heat dissipation, allowing operation at high current densities without a separate cooling system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an epitaxial layer is grown on a heterogeneous substrate (sapphire substrate), then the light emitting diode can be manufactured with lower costs, but the current density becomes high (1E8/cm2 or more) which limits improvement in luminous efficacy
Solution Approach 1:
The patent changes the substrate material parameter from heterogeneous sapphire substrate to homogeneous gallium nitride substrate. This fundamental parameter change resolves the contradiction by eliminating lattice mismatch and thermal expansion differences, enabling the LED to operate at low current density (1E6/cm2 or less) while maintaining manufacturability through direct growth of the epitaxial layer on the substrate.
2Illumination intensity
If the light emitting diode operates at high current density to increase light emission per unit area, then the quantity of light emitted increases, but severe drooping phenomenon occurs due to current crowding through dislocations causing deterioration in internal quantum efficiency
Solution Approach 1:
The patent changes the substrate homogeneity parameter to eliminate dislocations at the interface. By using a homogeneous gallium nitride substrate instead of a heterogeneous sapphire substrate, the patent enables high current density operation without current crowding through dislocations, thereby maintaining high internal quantum efficiency while achieving increased light emission per unit area.
3Illumination intensity
If the light emitting diode operates at high current density (150 A/cm2 or more), then increased light emission is achieved, but junction temperature increases significantly requiring a separate cooling system
Solution Approach 1:
The patent changes the thermal conductivity parameter by using a homogeneous gallium nitride substrate instead of a heterogeneous sapphire substrate. This improvement in thermal transport properties enables the LED to operate at high current density (150 A/cm2 or more) with elevated junction temperature (180°C or more) without requiring a separate cooling system, as the heat can be dissipated effectively through the substrate.
4Ease of manufacture
If the epitaxial layer thickness is kept thin (several micrometers) for cost reduction, then manufacturing costs decrease, but current spreading in the horizontal direction becomes difficult causing deterioration in luminous efficacy
Solution Approach 1:
The patent changes the substrate homogeneity parameter, which fundamentally alters the current spreading mechanism. With a homogeneous gallium nitride substrate, current spreading occurs uniformly through the thin epitaxial layer without being hindered by lattice mismatch or dislocations, thereby achieving both cost reduction through thin layer fabrication and maintained luminous efficacy.
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 LED achieves uniform current spreading and increased light emission per unit area, maintaining high efficiency and operating at elevated temperatures, exceeding the junction temperature of conventional LEDs by 30°C without the need for additional cooling.
Implementation Method 1
a gallium nitride substrate with inclined surfaces for enhanced heat dissipation
Data Source
AI summary
An LED includes a gallium nitride substrate, a first semiconductor layer disposed thereon, and a mesa including a second semiconductor layer disposed on the first semiconductor layer and an intervening active layer. A first contact layer includes an outer contact part in contact with the first semiconductor layer near an edge of the substrate and an inner contact part in contact with the first semiconductor layer within a region encompassed by the outer contact part. A second contact layer is disposed on the mesa in contact with the second semiconductor layer. An upper insulation layer has first and second opening parts overlapping the first and second contact layers. First and second electrode pads are electrically connected to the first and second contact layers through the first and second opening parts. The LED can be driven at 150-315 A/cm2 and has a maximum junction temperature of 150-190° C.