Sine Wave Diffraction Grating for Semiconductor Laser κL Reduction
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Solution Overview
Problem
Conventional semiconductor laser device manufacturing technologies face challenges in reducing the coupling coefficient κL due to limitations in diffraction grating height, leading to variations in device characteristics and deterioration of laser performance, particularly when attempting to lower κL while maintaining manufacturing restrictions and avoiding thermal decomposition issues.
Innovation Solution
The method involves forming a diffraction grating with a sine wave shape using in-situ vapor phase etching with halogen-based gases, allowing for a reduced height of 15 nm or lower while achieving a sine wave shape, which reduces κL and removes reactive products with deteriorated crystallinity, thereby improving optical output efficiency and reducing the oscillation threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the height of the diffraction grating is lowered to reduce κL, then the coupling coefficient κL is reduced, but etching controllability deteriorates and yield variations increase
Solution Approach 1:
The patent changes the etching parameters by introducing a vapor phase etching step with halogen-based gas after the initial dry etching. This two-stage etching process allows precise control of the diffraction grating height at 15 nm or lower while maintaining manufacturing precision. The vapor phase etching provides atomic-layer precision control that enables achieving the target height with sufficient margin even at ultra-low heights.
Solution Approach 2:
The patent replaces the conventional single dry etching process with a combined dry etching and vapor phase etching process. The vapor phase etching uses chemical vapor deposition technology to provide precise material removal control, substituting the purely mechanical/physical sputtering process with a chemically-controlled process that offers superior precision at ultra-thin dimensions.
2Length of stationary object
If thermal decomposition is used to lower the diffraction grating height, then the height is reduced, but mass transport produces reaction products with low crystallinity that deteriorate laser device characteristics
Solution Approach 1:
The patent replaces thermal decomposition with vapor phase etching using halogen-based gas. Instead of using heat to remove material (which causes mass transport and crystallinity degradation), the process uses chemical etching at lower temperatures. This substitution eliminates the mass transport issue while achieving the same height reduction goal, maintaining the crystallinity and optical characteristics of the diffraction grating.
Solution Approach 2:
The patent introduces halogen-based gas as an intermediary substance to enable material removal without thermal decomposition. The halogen gas acts as a chemical mediator that etches the diffraction grating layer precisely without causing the mass transport and crystallinity degradation associated with thermal processes. This intermediary enables height control while preserving material quality.
3Loss of energy
If the diffraction grating is formed in a sine wave shape to reduce κL, then κL is reduced by 21.5%, but it is difficult to form this shape through conventional etching methods
Solution Approach 1:
The patent applies periodic action by using interference exposure during photolithography to directly pattern the sine wave shape in the resist. The interference pattern creates the periodic sine wave modulation that is transferred through the etching process. This approach makes the sine wave shape formation as easy as conventional rectangular patterning, eliminating the manufacturing difficulty while achieving the 21.5% reduction in κL.
Solution Approach 2:
The patent implements curvature by forming the diffraction grating with a sine wave cross-sectional shape instead of a rectangular shape. The curved sine wave profile is achieved through interference lithography followed by etching, allowing the grating to have the optimal curved geometry for reducing the coupling coefficient while maintaining ease of manufacture through standard photolithography techniques.
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 κL, enhances optical output efficiency, and improves device reliability by achieving a sine wave shape with reduced height, resulting in a 21.5% reduction in κL compared to rectangular shapes and increasing device yield from 70% to 90%.
Implementation Method 1
forming a diffraction grating with a sine wave shape using in-situ vapor phase etching with halogen-based gases
Implementation Method 2
a distributed feedback (DFB) laser using a refractive-index-modulation diffraction grating, which has narrow spectrum and allows single mode oscillation
Data Source
Figure 1~2
Figure 3A~3D
Figure 4A~4C
AI summary
A method of manufacturing semiconductor laser device capable of reducing κL, with manufacturing restrictions satisfied, is provided. In a distributed-feedback or distributed-reflective semiconductor laser device, immediately before burying regrowth of a diffraction grating, halogen-based gas is introduced to a reactor, and etching is performed on the diffraction grating so that each side wall has at least two or more crystal faces and a ratio of length of an upper side (L1) in a waveguide direction to a bottom side (Lo) parallel to a [100] surface is 0 to 0.3. And, a reactive product formed on side surfaces of the diffraction grating and in trench portions between stripes of the diffraction grating at an increase of temperature for regrowth is removed. Therefore, the diffraction grating with reduced height and a sine wave shape is obtained, thereby κL of the device is reduced. Thus, an oscillation threshold and optical output efficiency can be improved.