Superlattice UV LED Structure for Vertical Light Extraction
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Solution Overview
Problem
Deep ultraviolet light emitting diodes (UV LEDs) based on group III metal nitride semiconductors face challenges due to poor crystalline structural quality, internal charge sheets, and high refractive index, leading to inefficient light emission, especially in the vertical direction, and complexities in growing diverse alloy compositions for epitaxial stacks.
Innovation Solution
The development of an optoelectronic device with a semiconductor structure comprising superlattices made of distinct single crystal layers, specifically designed for efficient ultraviolet light emission, including a p-type and n-type active region with an i-type region in between, where the unit cells have varying alloy content to control electronic and optical properties, and the use of metallic reflectors for vertical cavity emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high aluminium content AlGaN alloy is used to obtain required bandgap for deep ultraviolet emission, then the optical emission wavelength is achieved, but the crystalline structural quality deteriorates and internal charge sheets are formed
Solution Approach 1:
The patent divides the active region into multiple quantum wells separated by barrier layers, creating a superlattice structure. This segmentation allows the use of high aluminium content materials in controlled thin layers rather than bulk, maintaining the required bandgap while reducing the accumulation of crystalline defects and internal charges that would occur in thick high-Al layers.
Solution Approach 2:
The patent applies different aluminium compositions locally within the active region - high aluminium content in quantum well layers for desired emission wavelength, and adjusted aluminium content in barrier layers for strain management. This local variation of material composition optimizes both optical emission properties and crystalline structural quality in different spatial locations.
2Reliability
If c-plane oriented group III metal nitride films are used to achieve highest crystalline structure quality, then the crystalline quality is improved, but internal pyroelectric and piezoelectric charges are generated
Solution Approach 1:
The patent extracts or removes the harmful internal charges by designing quantum well structures where the polarization effects are minimized through careful selection of layer thicknesses and compositions. The thin quantum well layers reduce the accumulation of pyroelectric and piezoelectric charges while maintaining crystalline quality from c-plane orientation.
Solution Approach 2:
The patent changes the structural parameters of the quantum wells - specifically the thickness and composition of alternating layers - to modify the polarization field distribution. By adjusting these parameters, the internal electric fields from pyroelectric and piezoelectric charges are reduced while preserving the benefits of c-plane crystalline orientation.
3Ease of manufacture
If traditional LED structure is used for deep ultraviolet emission, then the device can be manufactured, but the light emission intensity in vertical direction is poor
Solution Approach 1:
The patent transitions from traditional planar LED structure to a vertically stacked quantum well superlattice structure. This dimensional reorganization allows light emission in the vertical direction by aligning the quantum well planes perpendicular to the substrate, enabling efficient vertical light extraction while maintaining manufacturability through standard epitaxial growth techniques.
4Illumination intensity
If surface texturing is applied to improve light escape cone, then light emission is improved, but the complexity of device structure increases
Solution Approach 1:
The patent converts the high refractive index of group III metal nitride materials, which traditionally causes total internal reflection and poor light extraction, into a benefit by using it to confine carriers within the quantum wells for more efficient radiative recombination. The intrinsic optical properties are thus converted from a harmful factor to a useful feature for enhancing light emission efficiency without additional surface 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
This configuration enhances the optical emission intensity and efficiency of deep UV LEDs, allowing for improved light extraction and emission in the desired wavelength range, overcoming the limitations of traditional UV LEDs.
Implementation Method 1
deep ultraviolet light emitting diodes (UV LEDs) based on group III metal nitride semiconductors... the emission of deep ultraviolet light from crystalline AlGaN films... deep ultraviolet LEDs are traditionally formed using a high aluminium content AlGaN alloy in order to obtain the required bandgap for the desired optical emission wavelength
Implementation Method 2
UV LEDs have been unable to emit light efficiently in a vertical direction... the use of optical coupling structures, such as photonic bandgap patterned structures
Data Source
AI summary
An optoelectronic device comprising a semiconductor structure includes a p-type active region and an n-type active region. The semiconductor structure is comprised solely of one or more superlattices, where each superlattice is comprised of a plurality of unit cells. Each unit cell comprises at least two distinct substantially single crystal layers.