Transparent Oxide Contact for n-Type AlInGaP MicroLED Light Extraction
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Solution Overview
Problem
Existing AlInGaP LEDs and microLEDs face challenges in making electrical contact to the n-type layer without obstructing light transmission and in reducing optical cross-talk between adjacent LEDs, while maintaining high reflectivity and current spreading efficiency.
Innovation Solution
A transparent conductive oxide layer, such as Indium Tin Oxide (ITO) or Aluminum-doped Zinc Oxide (AZO), is used to make Ohmic contact with the n-type AlInGaP layer, allowing for efficient current spreading and reducing optical cross-talk by being thinner than conventional n-type layers, and improving reflectivity at the metal contact interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a metal contact is disposed directly on the n-type AlInGaP layer, then electrical contact is achieved, but light transmission is obstructed and reflectivity is reduced
Solution Approach 1:
A transparent conductive oxide layer is introduced as an intermediary between the metal contact and the n-type AlInGaP layer. This intermediate layer allows light to pass through while maintaining electrical contact, resolving the contradiction between light transmission and electrical contact reliability.
Solution Approach 2:
The patent uses composite material structure combining transparent conductive oxide with metal contact layers. This composite approach enables simultaneous achievement of optical transparency and electrical conductivity, which cannot be achieved with single materials alone.
2Reliability
If a thick n-type AlInGaP layer is used to form shared electrical contact between adjacent LEDs, then electrical connectivity is improved, but optical cross-talk increases
Solution Approach 1:
The transparent conductive oxide layer serves as a mediator that enables electrical connectivity while minimizing optical interference. Its thin nature compared to conventional n-type layers allows it to conduct electricity between adjacent LEDs without causing significant optical cross-talk.
Solution Approach 2:
The patent changes the thickness parameter of the contact layer from conventional thick n-type layers (2-3 microns) to a thin transparent conductive oxide layer. This parameter change reduces optical cross-talk while maintaining sufficient electrical connectivity through the transparent conductive material's properties.
3Productivity
If a transparent conductive oxide layer is introduced, then light transmission and current spreading are improved, but device complexity increases
Solution Approach 1:
The transparent conductive oxide layer performs multiple functions simultaneously: it provides electrical contact, enables current spreading, and maintains optical transparency. This multi-functionality reduces the need for separate layers for each function, thereby limiting the increase in device complexity.
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
Enhances light output power and design flexibility by allowing unobstructed light transmission and minimizing optical cross-talk, while providing a smooth interface for improved reflectivity and current distribution.
Implementation Method 1
A light emitting diode (LED) having a largest dimension of less than or equal to about 50 microns parallel to the layers forming the diode junction is referred to herein as a microLED. In operation of an LED, a forward bias is applied across a diode junction in the LED and radiative recombination of injected electrons and holes results in the emission of light.
Implementation Method 2
the reflectivity at the interface with the n-type AlInGaP layer is greater than it would be if the metal contact were disposed directly on the n-type AlInGaP layer. Hence the transparent conductive oxide ohmic contact layer may be used to improve a reflective mirror function of an n-side metal contact for directing light out of the LED.
Implementation Method 3
In operation of an LED, a forward bias is applied across a diode junction in the LED and radiative recombination of injected electrons and holes results in the emission of light.
Data Source
AI summary
AlInGaP LEDs and microLEDs comprise a transparent conductive oxide (TCO) layer disposed on and making Ohmic contact to an n-type AlInGaP layer. The TCO layer may be used to make electrical contact to the n-type side of the diode junction in the LED without obstructing transmission of light out of the LED through the n-type surface on which the TCO layer is disposed. The TCO layer may improve n-side current spreading. The TCO layer may be used to interconnect the n-side contacts of adjacent AlInGaP microLEDs in an array to form a shared n-side electrical contact with little or no optical cross-talk. The TCO layer may improve the reflectivity of an n-side metal contact arranged to direct light out of the LED.