Vertical LED Spacer Layer Photon Extraction
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Solution Overview
Problem
Conventional LEDs and VLEDs suffer from poor luminous efficiency due to photon absorption and misdirection by the p-doped layer, leading to reduced light extraction.
Innovation Solution
Incorporating a spacer layer between the active and p-doped layers to increase the distance for photon reflection and using a reflective layer to direct photons back into the intended emission path, along with a thick conductive metal layer for heat dissipation and improved current handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the p-doped layer is made thicker to improve current conduction, then electrical conductivity is improved, but photon absorption increases and luminous efficiency deteriorates
Solution Approach 1:
The device is segmented into distinct functional regions: an n-type region for current injection, an active region for light generation, and a p-type region for current extraction. The n-type region thickness is optimized for electrical conduction while the active region is positioned to maximize light extraction before photons encounter the p-type layer, thus segmenting the conflicting requirements of current conduction and photon transmission.
Solution Approach 2:
The invention transitions from a conventional planar structure to a vertical structure where current flows vertically through the layers. This dimensional reorganization allows photons to be extracted laterally from the active region before traveling through the p-doped layer, effectively separating the current conduction path from the photon extraction path and reducing photon absorption losses.
2Loss of energy
If the p-doped layer is made thinner to reduce photon absorption, then luminous efficiency is improved, but current conduction capability deteriorates
Solution Approach 1:
The device structure segments the current conduction function across multiple regions: the n-type region provides robust current injection capability, while the p-type region is optimized for current extraction. This segmentation allows each region to be independently optimized - the n-type region can be thicker for reliable conduction while the p-type region remains thin to minimize photon absorption.
Solution Approach 2:
The active region acts as an intermediary between the n-type and p-type regions. It is positioned to receive carriers from the n-type region, generate photons through recombination, and allow photon extraction before carriers continue to the thin p-type layer. This intermediary positioning enables the thin p-type layer to suffice for current extraction without compromising overall device performance.
3Device complexity
If photons travel directly through the p-doped layer to the substrate, then device structure is simplified, but light extraction efficiency deteriorates
Solution Approach 1:
The invention inverts the conventional light extraction approach. Instead of relying on photons to pass through the p-doped layer to the substrate, the structure is designed so that photons are extracted laterally from the active region's side walls before encountering the p-type layer. This inversion of the extraction path eliminates the problem of photon absorption by the p-doped layer while maintaining structural simplicity.
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 luminous efficiency by maximizing photon escape and reducing absorption, while also improving manufacturing yields and reducing electrostatic discharge susceptibility.
Implementation Method 1
Some of the photons travel through the p-doped layer 110 and are reflected back due to the two different indices of refraction at an interface between two disparate entities according to Snell's Law
Implementation Method 2
the p-GaN layer 110 contains mid-gap states that may absorb the photons emitted from the active layer 108, thereby decreasing luminous efficiency with increased p-GaN layer thickness
Implementation Method 3
a thick conductive metal layer 310 is created above the reflective layer 308... the metal layer 310 dissipates heat more effectively than substrates
Data Source
AI summary
A vertical light-emitting diode (VLED) structure that may impart increased luminous efficiency over conventional LEDs and VLEDs is described. As additional benefits, some embodiments may have less susceptibility to electrostatic discharge (ESD) and higher manufacturing yields than conventional devices. To accomplish these benefits, embodiment of the invention may utilize a spacer or other means to separate the p-doped layer from the active layer, thereby increasing the distance between the active layer and the reflective layer within the VLED structure.