Micron-Sized LED Mesa Reflective Collimation
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Solution Overview
Problem
Micro light emitting diodes (μLEDs) face efficiency challenges at low or high current densities due to non-radiative recombination and surface recombination losses, particularly in small sizes used for augmented reality displays and scanning applications, where efficiency can be less than 5% at low current densities and up to 60% at higher current densities.
Innovation Solution
The design includes an epitaxial structure with a mesa and base configuration, featuring a thick confinement layer, a light generation area with multi-quantum wells, a thin confinement layer, and a reflective contact to collimate and direct light emitted from the light generation area to the light emitting surface, enhancing light extraction efficiency through careful shaping and reflective structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small size μLEDs are used for augmented reality displays, then device compactness is improved, but efficiency deteriorates to less than 5%
Solution Approach 1:
The patent transitions from conventional planar LED structures to vertically stacked three-dimensional architectures. Multiple light-emitting regions are arranged in vertical layers, enabling increased light output volume within a compact footprint. This vertical dimensionality allows small μLEDs to maintain high efficiency by providing sufficient active emission volume without increasing lateral device size.
Solution Approach 2:
The patent employs composite epitaxial structures combining multiple semiconductor material layers with different optical and electrical properties. These composite structures include specialized confinement layers, waveguide layers, and active regions that work together to enhance light extraction efficiency and reduce non-radiative recombination, thereby improving overall device efficiency at small scales.
2Ease of manufacture
If conventional LED structures are used, then manufacturing simplicity is maintained, but light extraction efficiency deteriorates
Solution Approach 1:
The patent divides the LED structure into multiple functional segments or layers, including separate confinement layers, waveguide layers, and active regions. Each layer is optimized for its specific function, allowing independent optimization of light extraction while maintaining a systematic manufacturing approach that builds the complex structure through sequential epitaxial growth steps.
Solution Approach 2:
The patent implements local quality variations within different regions of the LED structure. Specific layers are designed with tailored optical properties (refractive indices, thicknesses) to optimize light extraction at particular interfaces. For example, confinement layers are positioned and dimensioned to create total internal reflection at specific locations, enhancing light extraction efficiency without requiring complete structural redesign.
3Illumination intensity
If high current density is applied to improve brightness, then light output is improved, but non-radiative recombination losses increase
Solution Approach 1:
The vertical stacking architecture distributes current injection across multiple parallel active regions in the vertical dimension. This allows total current to be divided among several emission zones, reducing current density in each individual region while maintaining high overall brightness. The multi-layer structure effectively increases the total emitting area without increasing lateral device footprint.
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 configuration significantly improves light extraction efficiency and brightness by collimating light output, addressing the efficiency issues at various current densities and sizes, particularly for small μLEDs used in 2D displays and 1D arrays.
Implementation Method 1
A reflective contact is on the contact layer to reflect a portion of the back emitted light from the light generation area
Implementation Method 2
Lateral travelling light from the light generation area is reflected (by 90° at parabolic mesa) at the mesa facet and the reflective contact
Implementation Method 3
directed through the base (as a collimated beam, such as for parabolic or conical reflector type) to the light emitting surface
Implementation Method 4
a light generation area (e.g., including a multi-quantum well (MQW)) on the thick confinement layer to emit light
Data Source
AI summary
A emitting diode (LED) includes an epitaxial structure defining a base and a mesa on the base. The base defines a light emitting surface of the LED and includes current spreading layer. The mesa includes a thick confinement layer, a light generation area on the thick confinement layer to emit light, a thin confinement layer on the light generation area, and a contact layer on the thin confinement layer, the contact layer defining a top of the mesa. A reflective contact is on the contact layer to reflect a portion of the light emitted from the light generation area, the reflected light being collimated at the mesa and directed through the base to the light emitting surface. In some embodiments, the epitaxial structure grown on a non-transparent substrate. The substrate is removed, or used to form an extended reflector to collimate light.