Graded AlGaN Alloy Layers for Polarization-Induced p-Type Junctions

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Solution Overview

Problem

The challenge in realizing p-n junctions using aluminum gallium nitride (AlGaN) based semiconductors lies in p-type doping, where high acceptor ionization energy and poor ionization lead to low free carrier concentrations and increased on-resistance, along with issues like surface polarity inversion and optical losses.

Innovation Solution

The solution involves leveraging spontaneous and piezoelectric polarization in wurtzite III/V nitride semiconductors through spatial compositional grading of AlGaN along the polar axis, creating a fixed bulk 3D polarization bound charge that enables the formation of mobile 3-dimensional holes without intentional doping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If high concentration of Mg is used for p-type doping, then free carrier concentration increases, but on-resistance increases and efficiency drops

Engineering Contradiction:

Improvefree carrier concentrationVSAvoidefficiency

Core Design Contradiction:

Quantity of substanceVSLoss of energy

Solution Approach 1:

The patent changes the doping mechanism from intentional Mg doping to polarization-induced doping by modifying the compositional parameter (Al content) in AlGaN layers. This creates a gradient in polarization charge density that generates holes without the harmful effects of high Mg concentration, resolving the contradiction between achieving sufficient carrier concentration and maintaining device efficiency

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the chemical doping mechanism (Mg diffusion) with a physical mechanism (polarization charge separation). By utilizing the spontaneous and piezoelectric polarization effects in wurtzite AlGaN, holes are generated through field-induced carrier separation rather than chemical doping, eliminating the associated defects and efficiency losses

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Quantity of substance

If Mg doping is used to create p-type region, then hole concentration increases, but on-resistance increases

Engineering Contradiction:

Improvehole concentrationVSAvoidon-resistance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent introduces an intermediary mechanism - the polarization field - to generate holes. Instead of directly doping with Mg, the compositional gradient in AlGaN creates a polarization charge distribution that acts as an intermediary to produce the desired hole concentration without the resistance penalty associated with Mg doping

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If Mg-doped cladding layers are used in waveguides, then p-type doping is achieved, but optical losses increase

Engineering Contradiction:

Improvep-type doping capabilityVSAvoidoptical losses

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent replaces chemical doping with polarization-induced doping in the waveguide cladding layers. This substitution eliminates Mg-related optical absorption and scattering, achieving p-type characteristics through electric field effects that are transparent to UV radiation, thus maintaining low optical losses

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Quantity of substance

If conventional p-type doping is used in AlGaN, then acceptor ionization energy is high, but ionization is poor

Engineering Contradiction:

Improvefree carrier concentrationVSAvoidionization energy

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

The patent replaces thermal ionization (which requires overcoming high acceptor binding energy) with field-induced ionization. The strong polarization field in the compositional gradient directly extracts electrons from acceptors, enabling ionization without requiring thermal energy to overcome the high binding energy barrier

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 effectively induces a high-density distribution of holes, improving the efficiency of p-n junctions and reducing on-resistance, while also minimizing optical losses and other doping-related issues.

Implementation Method 1

leveraging spontaneous and piezoelectric polarization in wurtzite III/V nitride semiconductors through spatial compositional grading of AlGaN along the polar axis, creates a fixed bulk 3D polarization bound charge

Methodology Applied

Scientific EffectSpontaneous polarization: Polarisation

Implementation Method 2

Methodology Applied

Scientific EffectPiezoelectric polarization: Piezoelectric Effect

Data Source

PatentUS20250194189A1Devices with compositionally graded alloy layers

Publication Date: 2025.06.12 CORNELL UNIVERSITY

AI summary

A semiconductor device that includes at least one not intentionally doped compositionally graded ternary, quaternary, quinary or senary ultra-wide bandgap alloy layer. Composition grading along a predetermined axis and changes in energy bandgap in space by compositional grading, alloy material, and effects of said any adjacent layers results in the at least one not intentionally doped compositionally graded ternary, quaternary, quinary or senary ultra-wide bandgap alloy layer being one of an n-type layer with a density distribution of electrons or a p-type layer with a density distribution of holes, depending on design choices. The at least one not intentionally doped compositionally graded ternary, quaternary, quinary or senary ultra-wide bandgap alloy layer is disposed on a substrate layer.