InGaN Laser Diode Waveguide Cladding for Blue Green Light

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Solution Overview

Problem

Conventional III-V compound nitride lasers face challenges in achieving large refractive index differentials between cladding layers and the active region due to lattice mismatch, leading to reduced optical confinement and high modal losses, which increase the threshold current and impair laser operation.

Innovation Solution

Incorporating indium gallium nitride (InGaN) semiconductor lasers with a group III-V nitride waveguide layer that includes indium, enhancing both electrical and optical confinement by reducing lattice mismatch and increasing the indium content in the quantum wells for blue and green wavelength lasers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If AlGaN cladding layers are used to achieve refractive index differential, then optical confinement is improved, but lattice mismatch limits maximum thickness and alloy composition

Engineering Contradiction:

Improveoptical confinementVSAvoidlattice mismatch constraints

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the compositional parameters of the cladding layer by incorporating indium into the GaN lattice to form InGaN. This parameter change allows achieving the desired refractive index differential without being constrained by the severe lattice mismatch problems that limit AlGaN alloy composition and thickness.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite material approach by creating InGaN alloys with specific indium compositions (e.g., In0.03Ga0.97N, In0.05Ga0.95N) that combine the benefits of GaN's wide bandgap with indium's ability to adjust refractive index, thereby achieving both optical confinement and structural compatibility.

Inventive Principle:

Principle #40Composite materials

2Reliability

If AlGaN cladding layers are doped with Mg to facilitate current flow, then electrical conductivity is improved, but high hole concentrations are difficult to achieve due to increased ionization energy

Engineering Contradiction:

Improveelectrical conductivityVSAvoidionization energy

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the material composition parameter by substituting Al with In in the cladding layer. This composition change reduces the ionization energy of Mg acceptors, enabling higher hole concentrations and improved electrical conductivity without the energy penalties associated with AlGaN:Mg systems.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If Al is eliminated from cladding layers to avoid Mg-Al conflict, then electrical conductivity is improved, but optical mode confinement weakens and transverse optical mode penetration increases

Engineering Contradiction:

Improveelectrical conductivityVSAvoidoptical mode confinement

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent simultaneously optimizes two parameters: indium composition (3-20% In) and doping concentration (1e19 to 1e21 atoms/cm³). This dual parameter optimization enables the InGaN cladding to provide both strong optical confinement through refractive index differential and high electrical conductivity through enhanced hole concentration, resolving the trade-off between these two functions.

Inventive Principle:

Principle #35Parameter changes

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

The use of InGaN waveguides improves optical confinement and reduces modal losses, leading to more efficient laser operation with lower threshold currents and enhanced performance in blue and green wavelength lasers.

Implementation Method 1

An upper cladding layer above the core and a lower cladding layer below the core have refractive indexes lower than the core refractive index. The cladding lower refractive indexes form a waveguide effect that contains the optical modes in the core.

Methodology Applied

Scientific EffectOptical waveguide effect: Waveguide (optics)

Implementation Method 2

Adding indium to the cladding or waveguide layer reduces the lattice mismatch between the waveguide and the multiple quantum well active region.

Methodology Applied

Scientific EffectLattice mismatch reduction:

Data Source

PatentUS7751455B2Blue and green laser diodes with gallium nitride or indium gallium nitride cladding laser structure

Publication Date: 2010.07.06 GENESEE VALLEY INNOVATIONS LLC

AI summary

A novel indium gallium nitride laser diode is described. The laser uses indium in either the waveguide layers and/or the cladding layers. It has been found that InGaN waveguide or cladding layers enhance optical confinement with very small losses. Furthermore, the use of InGaN waveguide or cladding layers can improve the structural integrity of active region epilayers because of reduced lattice mismatch between waveguide layers and the active region.