AlGaInAs Graded Layer for InP Modulator Band Discontinuity

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Solution Overview

Problem

Conventional electro-absorption modulators face challenges with band discontinuity, particularly on the p-side, which hinders high-speed operation due to energy barriers and potential wells, when AlGaInAs-based materials are used for the MQW active layer and InGaAsP-based materials for the SCH graded layers, leading to impaired carrier movement and response characteristics.

Innovation Solution

The semiconductor device employs a configuration with AlGaInAs-based and InGaAsP-based semiconductor layers, where the AlGaInAs-based p-side SCH graded layer has a composition that matches the AlGaInAs-based MQW active layer on one side and InGaAsP-based p-side SCH graded layer on the other, ensuring continuous band gap variation and equal valence band maximum energy levels, eliminating band discontinuity and facilitating high-speed carrier transport.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If AlGaInAs-based material is used for MQW active layer and InGaAsP-based material for SCH graded layers, then device performance (extinction ratio, temperature characteristic) is improved, but band discontinuity occurs causing energy barriers and potential wells that hinder high-speed operation

Engineering Contradiction:

Improvedevice performanceVSAvoidoperation speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

An AlGaInAs-based graded layer is introduced as an intermediary between the AlGaInAs-based MQW active layer and the InGaAsP-based SCH graded layer. This intermediate layer has a composition that gradually transitions from AlGaInAs to InGaAsP, eliminating the abrupt band discontinuity and preventing energy barriers and potential wells that would otherwise hinder carrier movement and high-speed operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The composition of the AlGaInAs-based graded layer is continuously varied to achieve a gradual transition in band gap energy. By adjusting the Al, Ga, and In composition ratios along the gradient, the energy band structure is optimized to eliminate discontinuities while maintaining lattice matching, thereby enabling high-speed carrier transport across the heterostructure interface.

Inventive Principle:

Principle #35Parameter changes

2Speed

If graded layers with continuous composition variation are introduced to eliminate band discontinuity, then carrier movement is improved, but device structure complexity increases

Engineering Contradiction:

Improvecarrier movement speedVSAvoidlayer structure complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The AlGaInAs-based graded layer is strategically positioned only at the critical interface between the AlGaInAs MQW active layer and the InGaAsP SCH graded layer, where band discontinuity occurs. This localized approach addresses the specific problem area without requiring complex graded structures throughout the entire device, thereby minimizing overall structural complexity while effectively improving carrier movement at the critical interface.

Inventive Principle:

Principle #3Local quality

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 configuration enables high-speed operation by preventing energy barriers for holes and effective potential wells for electrons, enhancing device performance, including extinction ratio and temperature characteristics, and improving modulation and response characteristics compared to conventional modulators.

Implementation Method 1

the composition of the second semiconductor layer continuously varies such that a band gap continuously increases from the first semiconductor layer side toward the third semiconductor layer side

Methodology Applied

Scientific EffectBand gap variation:

Implementation Method 2

the compositions of the second and third semiconductor layers are set such that energy levels of a valence band maximum are equal to or substantially equal to each other on an interface between the second and third semiconductor layers

Methodology Applied

Scientific EffectEnergy level alignment:

Implementation Method 3

a reverse bias electric field is applied to the MQW active layer 103 by the upper and lower electrodes 107 and 108 to vary the absorption coefficient for light propagating in the MQW active layer 103 thereby to modulate (intensity modulate) the intensity of the light

Methodology Applied

Scientific EffectElectro-absorption: Electro-Optic Effects

Data Source

PatentUS7889773B2Semiconductor device

Publication Date: 2011.02.15 FUJITSU LTD

AI summary

A semiconductor device includes an InP substrate, an AlGaInAs-based first layer, an AlGaInAs-based second layer, an InGaAsP-based third layer, and an InGaAsP-based fourth layer. The first and second layers have compositions which are same or substantially same as each other on an interface therebetween. The composition of the layer varies such that a band gap continuously increases from the first layer side toward the third layer side. The compositions of the second and third layers are set such that energy levels of a valence band maximum are substantially equal to each other on an interface between the second and third layers. The composition of the third layer varies such that a band gap continuously increases from the second layer side toward the fourth layer side. The compositions of the third and fourth layers are same or substantially same as each other on an interface between the third and fourth layers.