Semiconductor Laser Electrode Refractive Index Management
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Solution Overview
Problem
Ridge waveguide semiconductor laser devices with current constriction by Schottky junctions suffer from light leakage to electrodes due to similar refractive indices, leading to increased internal loss and reduced slope efficiency.
Innovation Solution
A ridge waveguide semiconductor laser device with an upper electrode comprising a high refractive index layer (>2.5) and a low refractive index layer (≤1.0) is used, where the high refractive index layer is limited to a thickness of not greater than 75 nm, and the low refractive index layer is used to prevent light leakage and reduce photoabsorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the electrode is put in direct contact with the side surfaces of the ridge portion to simplify manufacturing, then manufacturing cost is reduced, but light leakage to the electrode occurs due to similar refractive indices, increasing internal loss
Solution Approach 1:
The electrode structure is segmented into multiple functional layers: a Schottky junction formation layer (Ti/Pt) for current constriction, a light-blocking layer (Ni) to prevent light leakage, and a contact layer (Au) for electrical connection. This segmentation allows each layer to perform its specific function while collectively resolving the contradiction between manufacturing simplicity and light leakage prevention.
Solution Approach 2:
The Ni light-blocking layer acts as an intermediary between the Ti/Pt Schottky junction layer and the Au contact layer. This intermediate layer specifically addresses the light leakage problem by absorbing or reflecting light that would otherwise escape to the electrode, while maintaining the electrical functionality of the electrode structure.
2Device complexity
If current constriction is effected by Schottky junction without insulator to simplify manufacturing, then manufacturing processes are simplified, but light leakage toward electrode increases due to refractive index matching
Solution Approach 1:
The electrode is divided into functional segments where Ti/Pt forms the Schottky junction for current constriction, Ni provides light blocking to prevent light leakage, and Au serves as the contact layer. This segmentation maintains manufacturing simplicity while improving reliability by addressing light leakage through the Ni layer.
Solution Approach 2:
The electrode uses a composite multi-layer structure combining different materials (Ti, Pt, Ni, Au) each selected for specific properties. Ti and Pt provide Schottky junction characteristics, Ni provides light-blocking properties, and Au provides excellent electrical conductivity. This composite structure resolves the contradiction between simple manufacturing and high reliability.
3Ease of operation
If high refractive index electrode materials are used for current constriction, then current flow control is improved, but light leakage to electrode increases due to refractive index similarity with semiconductor material
Solution Approach 1:
The electrode structure separates the current constriction function (Ti/Pt layers with high refractive index) from the light-blocking function (Ni layer). The Ti/Pt layers maintain good current flow control due to their high refractive index, while the Ni layer specifically prevents light leakage by absorbing or reflecting light that would otherwise be guided into the electrode.
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 reduces internal loss, lowers the oscillation threshold current, and enhances slope efficiency while maintaining low manufacturing costs.
Implementation Method 1
the upper electrode having a high refractive index layer and a low refractive index layer formed successively from a side put in contact with the semiconductor layer group, the high refractive index layer having a refractive index of not lower than 2.5 with respect to a wavelength band of emission laser light and the low refractive index layer having a refractive index of not higher than 1.0
Implementation Method 2
a Schottky junction portion is formed between the p-InGaP cladding layer and the p-electrode, and a current flows only between the p-electrode and the p-InGaAs contact layer, effecting the current constriction
Data Source
AI summary
In a semiconductor laser device, a p-side electrode (114) of a multilayer structure put in contact with the surface of a ridge portion (130) of a second conductive type semiconductor layer group (p-AlGaAs first upper cladding layer (108), p-AlGaAs second upper cladding layer (109), p-GaAs etching stop layer (110), p-AlGaAs third upper cladding layer (111), p-GaAs contact layer (112) and p+-GaAs contact layer (113)) is formed. The p-side electrode (114) has one or a plurality of high refractive index layers and low refractive index layers formed successively from the side put in contact with the surface of the semiconductor layer group of the second conductive type. The high refractive index layers have a refractive index of not lower than 2.5 with respect to the wavelength band of the emission laser light and a total thickness of not greater than 75 nm, while the low refractive index layers have a refractive index of not higher than 1.0 with respect to the wavelength band of the emission laser light.