GaN Substrate Dislocation Control via Segmented Ge Doping

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Solution Overview

Problem

Gallium nitride single crystal substrates face challenges in reducing dislocations with large strain fields, which adversely affect device characteristics, as existing methods struggle to universally identify and mitigate these defects effectively.

Innovation Solution

The method involves growing a gallium nitride single crystal substrate with a high concentration of germanium doping in the inclined interface growth region, using a specific growth process that reduces dislocations with large strain fields by bending and pinning them, resulting in a substrate with minimal etch pits exceeding a certain diameter when etched with an alkaline solution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional growth methods are used to produce gallium nitride single crystal substrates, then manufacturing simplicity is maintained, but dislocations with large strain fields cannot be effectively reduced, adversely affecting device characteristics

Engineering Contradiction:

Improvedevice characteristicsVSAvoidgrowth process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The growth process is divided into multiple distinct stages: initial growth stage, intermediate growth stage, and final growth stage. Each stage has specific doping concentration ranges and growth conditions optimized for that phase, allowing systematic control of dislocation evolution without requiring a completely complex new approach

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes key growth parameters over time, specifically the germanium doping concentration which evolves from 1×10^18 to 1×10^20 atoms/cm³ during the growth process. This dynamic parameter adjustment enables effective dislocation control while maintaining process manageability

Inventive Principle:

Principle #35Parameter changes

2Reliability

If germanium doping is applied to reduce dislocations with large strain fields, then device characteristics improve, but the manufacturing precision requirements increase due to strict control of doping concentration and etch pit density

Engineering Contradiction:

Improvedevice characteristicsVSAvoiddoping concentration control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention applies different doping concentrations at different growth stages rather than uniform doping throughout. The doping concentration is locally optimized for each stage: lower in initial growth, higher in intermediate growth, and controlled in final growth, reducing the overall precision burden compared to maintaining a single strict doping level

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Germanium doping is introduced in advance during the crystal growth process itself rather than as a separate post-processing step. This preliminary action during growth allows dislocations to be controlled as they form, making the precision requirements more manageable compared to attempting to correct dislocations after substrate completion

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the density of etch pits is reduced to minimize large strain field dislocations, then device characteristics improve, but the growth process becomes more complex requiring multiple controlled stages

Engineering Contradiction:

Improvedevice characteristicsVSAvoidmulti-stage growth process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The multi-stage growth process operates continuously without interruption, with each stage transitioning smoothly into the next. The germanium doping is introduced and adjusted continuously during growth rather than through discrete interruptions, maintaining productive action throughout while achieving the desired etch pit density reduction

Inventive Principle:

Principle #20Continuity of useful action

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 reduces dislocations with large strain fields, leading to improved device characteristics by increasing the abundance ratio of dislocations with small strain fields and minimizing the number of etch pits with diameters exceeding a certain threshold, thereby enhancing the quality of devices fabricated on these substrates.

Implementation Method 1

a first step of directly epitaxially growing a group III nitride semiconductor single crystal having a top surface with exposed (0001) plane on the main surface of the base substrate

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Implementation Method 2

a density of etch pits when applying etching to the main surface with an alkaline etching solution is less than 1×10^6 cm^−2

Methodology Applied

Scientific EffectChemical etching:

Data Source

PatentUS12258678B2Gallium nitride single crystal substrate

Publication Date: 2025.03.25 SUMITOMO CHEM CO LTD

AI summary

There is provided a gallium nitride single crystal substrate, which is a gallium nitride single crystal substrate that has a diameter of 50 mm or more and whose low index crystal plane closest to a main surface is a (0001) plane, wherein a density of etch pits when applying etching to the main surface with an alkaline etching solution is less than 1×106 cm−2, and among peaks appearing in a histogram of diameters of the etch pits, when a diameter of a first peak appearing on a smallest diameter-side is a, a total number of the etch pits with a diameter exceeding 4a is 1/1000 or less of a number of etch pits forming the first peak.