Nanowire Light Emitting Device Piezoelectric Charge Separation
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Solution Overview
Problem
Conventional semiconductor light emitting diodes (LEDs) face challenges with high threading dislocation densities due to lattice mismatch, leading to poor deep ultraviolet emission intensity and efficiency, especially when using group III-nitride materials, which are plagued by crystalline defects and non-radiative recombination sites.
Innovation Solution
The development of nanowire light emitting devices with a semiconductor core and a cladding material having a higher breakdown voltage, where the nanowires are formed separately and attached to a substrate, allowing for charge separation and recombination without external electrodes, utilizing either an external electric field or mechanical strain in piezoelectric materials to induce electron-hole recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If group III-nitride semiconductor materials are used for deep ultraviolet LED emission, then the material system is established for DUV wavelength range, but high threading dislocation density and crystalline defects occur due to lattice mismatch with substrates
Solution Approach 1:
The invention segments the semiconductor structure into vertically stacked quantum wells separated by barrier layers, creating a multi-layered quantum dot system. This segmentation allows each quantum well to be independently optimized and reduces the propagation of threading dislocations through the structure, thereby improving crystalline quality while maintaining DUV emission intensity
Solution Approach 2:
The invention implements local quality enhancement by creating quantum dots with specific compositional gradients and sizes within the quantum wells. Each quantum dot region has tailored material composition (e.g., AlxGa1-xN with varying x) to optimize local band structure and carrier confinement, improving radiative recombination efficiency at defect-prone regions while maintaining overall structural integrity
2Use of energy by moving object
If conventional semiconductor junctions with p-type and n-type regions are used, then electrical energy conversion to optical energy is achieved, but non-radiative recombination at defect sites reduces internal quantum efficiency
Solution Approach 1:
The quantum dot structures serve multiple functions simultaneously: they act as carrier confinement regions, radiation emission centers, and defect tolerance zones. The vertically stacked quantum wells provide both optical confinement and electrical transport pathways, enabling the structure to maintain high internal quantum efficiency by directing carriers toward radiative recombination sites while minimizing non-radiative losses at interfaces
Solution Approach 2:
The invention converts the harmful effect of threading dislocations into a beneficial feature by positioning quantum dots at strategic locations where dislocations terminate or bend. The quantum dot composition and structure are designed to trap and neutralize dislocation-induced defects, transforming regions that would normally cause non-radiative recombination into active emission centers, thereby converting structural imperfections into functional advantages
3Device complexity
If nanowires are formed separately and attached to substrate without external electrodes, then device complexity is reduced and manufacturing is simplified, but charge separation and recombination mechanisms must be established through alternative means
Solution Approach 1:
The invention extracts and eliminates the need for external metal electrodes by utilizing the nanowire's intrinsic piezoelectric properties. The nanowire core itself serves as both the structural support and the active element for charge separation and recombination, removing complex electrode assemblies and simplifying the overall device architecture while maintaining functionality
Solution Approach 2:
The nanowire structure is designed to be self-sufficient by utilizing its inherent piezoelectric effect to generate internal electric fields for charge separation. The vertically stacked quantum wells within the nanowire automatically confine and recombine carriers through quantum mechanical effects without requiring external electrical contacts, enabling the device to function autonomously with simplified manufacturing
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 significantly reduces defect-related losses, enhances radiative recombination efficiency, and increases the light emission intensity, particularly in the deep ultraviolet range, achieving efficiencies up to 10% compared to conventional LEDs' 1% efficiency.
Implementation Method 1
The nanowire is attached to the substrate such that movement of the substrate creates and releases mechanical strain on the piezoelectric material of the core. The mechanical strain on the piezoelectric material of the core creates the cycling of the electrical field.
Data Source
AI summary
Light emitting device and methods for forming the devices include a substrate and a nanowire placed on the substrate, where the nanowire comprises a core made of a semiconductor material. A cladding encloses the nanowire and has a breakdown voltage larger than a breakdown voltage of the core. A source of an electric field is provided, where the core is at least partially aligned with and lies at least partially within the electric field such that a cycling of the electric field creates charge separation and electron-hole recombination in the core.