Impact-Ionization UVC LEDs Without p-Doping Barriers
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) face challenges in generating light at wavelengths below 250 nm due to inefficient p-doping in AlN, leading to a drop-off in radiative emission and compromised performance in ultraviolet-C (UVC) range, where p-GaN layers are highly absorbing and detrimental to horizontal light emission.
Innovation Solution
The implementation of an impact ionization layer and a charge layer with a net charge creates a barrier for carrier transport, allowing for light emission at UVC wavelengths without the need for p-doping, utilizing a unique n-i-c-im or p-i-c-im structure with a compositional or polarity-based barrier to achieve sufficient electric fields for impact ionization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If p-doping is used in AlN to achieve hole injection, then light emission at UVC wavelengths can be achieved, but p-doping efficiency is very low due to high activation energies
Solution Approach 1:
The patent extracts and removes the p-doped GaN layer from the device structure, replacing it with an intrinsic layer combined with impact ionization mechanism. This eliminates the harmful absorbing layer while maintaining hole generation capability through alternative physics-based hole generation rather than chemical doping
Solution Approach 2:
The patent substitutes the chemical doping mechanism (electrochemical process) with a physical impact ionization mechanism. Instead of relying on dopant atoms to generate carriers, the system uses high electric fields to accelerate electrons that then collide with valence band electrons to generate holes physically, replacing chemical substitution with physical acceleration and collision
2Productivity
If p-GaN layer is used for hole injection, then hole currents can be generated, but the layer is highly absorbing and detrimental to horizontally emitted light
Solution Approach 1:
The patent extracts and removes the p-GaN layer from the device structure, replacing it with an intrinsic layer combined with impact ionization mechanism. This eliminates the harmful absorbing layer while maintaining hole generation capability through alternative physics-based hole generation rather than chemical doping
Solution Approach 2:
The patent introduces an intrinsic layer as an intermediary between the n-doped layer and the light emission region. This intrinsic layer serves as a mediator where impact ionization occurs to generate holes without requiring a p-doped layer, thereby eliminating the absorption problem while maintaining hole injection function
3Ease of manufacture
If conventional LED structure is used for wavelengths below 250 nm, then device fabrication can proceed, but radiative emission drops off significantly
Solution Approach 1:
The patent changes the fundamental operating parameters of the LED by implementing a high electric field regime (exceeding the critical field for impact ionization) in the intrinsic layer. This parameter change enables efficient hole generation at UVC wavelengths through impact ionization, overcoming the radiative emission drop-off that occurs in conventional low-field LED structures
Solution Approach 2:
The patent introduces dynamic carrier multiplication through impact ionization, where injected electrons are accelerated by high electric fields to generate additional electron-hole pairs dynamically. This dynamic process enables sufficient carrier densities for efficient light emission at wavelengths below 250 nm without requiring static p-doping
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 enables efficient light generation in the UVC range by generating holes in the impact ionization layer, allowing recombination in an intrinsic region, thereby overcoming the limitations of p-doping and enhancing light emission efficiency and directionality.
Implementation Method 1
The charge layer forms a barrier for transporting carriers of the first conductivity type until a bias of at least 1.5 times a bandgap of the second material is applied
Implementation Method 2
a resulting electric field in the impact ionization layer is greater than or equal to an impact ionization threshold for the second material
Implementation Method 3
allowing recombination in an intrinsic region, thereby overcoming the limitations of p-doping and enhancing light emission efficiency
Data Source
AI summary
Embodiments disclose LEDs that operate using impact ionization. Devices include a first conductivity type layer having a first conductivity type, a first intrinsic layer, a charge layer, an impact ionization layer, and a contact layer. The charge layer has a net charge of the first conductivity type and has a material comprising a polar oxide or a non-polar oxide. The charge layer forms a barrier for transporting carriers of the first conductivity type until a bias is applied between the first conductivity type layer and the contact layer to flatten the barrier.