Columnar Quantum Dot Optical Semiconductor Device Strain Management

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Solution Overview

Problem

Optical semiconductor devices with quantum dots in active layers face challenges in achieving high luminous intensity of TM mode light with no polarization dependence due to strain issues in columnar dots, leading to reduced crystallinity and luminous efficiency.

Innovation Solution

The device incorporates a quantum structure with a side barrier composed of alternating layers with tensile and compressive strain, allowing for controlled strain distribution to maintain quantum dot formation and enhance luminous intensity, specifically by forming first and second side barrier layers with different lattice constants to manage strain effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the number of stacked layers of quantum dots is increased to increase the luminous intensity ratio of TM mode, then the polarization independence is achieved, but the crystallinity of the active layer deteriorates and the luminous intensity reduces

Engineering Contradiction:

Improvepolarization independenceVSAvoidcrystallinity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The side barrier is divided into multiple side barrier layers, each with different lattice constants. This segmentation allows different portions of the side barrier to provide different strain effects, enabling the columnar dot to maintain good crystallinity while achieving polarization independence through multiple stacked quantum dots.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different side barrier layers are assigned different lattice constants to create localized strain distributions. The first side barrier layer with smaller lattice constant provides tensile strain, while the second side barrier layer with larger lattice constant provides compressive strain, allowing precise control of strain in different regions of the columnar dot structure.

Inventive Principle:

Principle #3Local quality

2Use of energy by moving object

If tensile strain is introduced into the side barrier to increase the luminous intensity of TM mode light, then the luminous efficiency is improved, but the quantum dot formation and crystallinity may be compromised

Engineering Contradiction:

Improveluminous efficiencyVSAvoidquantum dot formation

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The lattice constant of the side barrier material is changed by adjusting the composition ratio of InGaAsP. By varying the phosphor content, different lattice constants are achieved, allowing the side barrier to provide appropriate tensile or compressive strain to enhance TM mode luminous intensity while maintaining quantum dot formation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The side barrier is constructed as a composite structure with multiple layers of InGaAsP materials having different compositions. This composite structure enables simultaneous achievement of strain enhancement for TM mode and proper quantum dot formation by combining materials with different lattice constants.

Inventive Principle:

Principle #40Composite materials

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 polarization-independent optical amplification with increased luminous intensity of TM mode light, surpassing the limitations of previous strain management methods by ensuring proper quantum dot stacking and maintaining high crystallinity.

Implementation Method 1

a strain exists therein, and hence there is a problem that by stacking the quantum dots in layers, the crystallinity of the active layer deteriorates

Methodology Applied

Scientific EffectStrain: Deformation

Implementation Method 2

there is a method of introducing a tensile strain into the side barrier to relieve the strain accumulated in the columnar dot

Methodology Applied

Scientific EffectTensile strain: Deformation

Implementation Method 3

quantum dots can be formed on a substrate in the form of mutually isolated islands by utilizing a so-called S-K (Stranski-Krastanow) mode growth, which appears in the initial phase of heteroepitaxial growth

Methodology Applied

Scientific EffectHeteroepitaxial growth: Epitaxy

Implementation Method 4

the PL spectral intensity of the columnar dot when the number of stacked layers of quantum dots is 11 (11-fold columnar dot) reduces to about half as compared with a single-layer quantum dot

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Data Source

PatentUS7968868B2Optical semiconductor device and manufacturing method of the same

Publication Date: 2011.06.28 FUJITSU LTD

AI summary

A side barrier is provided between columnar dots each constituted by directly stacking respective quantum dots in seven or more layers. Out of respective side barrier layers composing the side barrier, each of the lower side barrier layers (four layers of the undermost layer to the fourth layer from the bottom) is formed as a first side barrier layer into which a tensile strain is introduced, and each of the upper side barrier layers (three layers of the fifth layer to the uppermost layer from the bottom) is formed as a second side barrier layer which has no strain.