III-Nitride LED Tunnel Junction for High Wall Plug Efficiency

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Solution Overview

Problem

Current III-nitride light-emitting diodes (LEDs) face challenges with p-GaN's difficulty in electrical contact and low hole concentration and mobility, leading to inefficiencies in current spreading and increased voltage, necessitating the use of alternative materials like transparent conducting oxides (TCOs) for current spreading.

Innovation Solution

Incorporating a tunnel junction with n-GaN as a current spreading layer, replacing traditional p-contacts and TCOs, and using a multilayer dielectric high reflectivity coating with an aluminum reflector to enhance light extraction and reduce voltage losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If traditional p-contacts and TCOs are used for current spreading in III-nitride LEDs, then electrical contact can be established, but voltage losses increase and efficiency decreases

Engineering Contradiction:

Improvevoltage lossVSAvoidelectrical contact difficulty

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The patent introduces an n-type GaN tunnel junction layer as an intermediary between the p-GaN contact layer and the underlying structure. This tunnel junction enables efficient electron injection and current spreading while avoiding the high voltage losses associated with traditional p-contacts and TCOs. The tunnel junction acts as a mediator that facilitates low-resistance electrical contact without requiring difficult-to-contact p-GaN layers.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the doping type and concentration parameters of the contact structure. Instead of using p-type contacts with low hole concentration and mobility, the invention uses highly doped n-type GaN layers with high electron concentration and mobility. This parameter change transforms the contact mechanism from hole-injection limited to electron-injection efficient, dramatically reducing voltage losses.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If p-GaN is used as current spreading layer, then current can be injected, but hole concentration and mobility are low leading to inefficiency

Engineering Contradiction:

Improvecurrent spreading efficiencyVSAvoidhole concentration and mobility

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent inverts the traditional approach by using n-type GaN instead of p-type GaN for current spreading. Instead of relying on low-mobility holes in p-GaN, the invention uses high-mobility electrons in n-GaN tunnel junction layers to achieve superior current spreading efficiency and reliability.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If traditional LED structure is used, then manufacturing is straightforward, but droop phenomenon occurs reducing efficiency at high currents

Engineering Contradiction:

Improvestructure simplicityVSAvoiddroop loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent employs a composite structure combining multiple n-type GaN layers with different doping concentrations (n-GaN tunnel junction layer, n+-GaN contact layers) with the traditional p-n junction. This composite n-type tunnel junction structure maintains manufacturing simplicity while effectively suppressing the droop phenomenon through enhanced current spreading and reduced carrier density in the active region.

Inventive Principle:

Principle #40Composite materials

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 achieves high wall plug efficiency and external quantum efficiency, with peak efficiencies of 72% and 78% respectively, and reduces the droop in III-nitride LEDs, improving light extraction and overall performance.

Implementation Method 1

a tunnel junction between a p-type III-nitride layer and a highly doped n-type III-nitride layer

Methodology Applied

Scientific EffectTunneling:

Implementation Method 2

multilayer dielectric high reflectivity coating with an aluminum reflector to enhance light extraction

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11164997B2III-nitride tunnel junction light emitting diode with wall plug efficiency of over seventy percent

Publication Date: 2021.11.02 RGT UNIV OF CALIFORNIA

AI summary

A III-Nitride LED which utilizes n-type III-Nitride layers for current spreading on both sides of the device. A multilayer dielectric coating is used underneath the wire bond pads, both LED contacts are deposited in one step, and the p-side wire bond pad is moved off of the mesa. The LED has a wall plug efficiency or External Quantum Efficiency (EQE) over 70%, a fractional EQE droop of less than 7% at 20 A/cm2 drive current and less than 15% at 35 A/cm2 drive current. The LEDs can be patterned into an LED array and each LED can have an edge dimension of between 5 and 50 μm. The LED emission wavelength can be below 400 nm and aluminum can be added to the n-type III-Nitride layers such that the bandgap of the n-type III-nitride layers is larger than the LED emission photon energy.