Diffraction Grating Fabrication for Semiconductor Lasers
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Solution Overview
Problem
Current methods for fabricating diffraction gratings in semiconductor lasers, such as electron beam exposure and holographic exposure, face challenges in achieving precise control over the period of the grating, particularly for shorter wavelengths like 532 nm, leading to inefficiencies and difficulties in volume production and higher light scattering losses.
Innovation Solution
A method involving the formation of a multilayer structure with alternating first and second diffraction grating layers, where the second grating layer is selectively grown in the grooves of the first grating layer, allowing for the creation of a first-order diffraction grating with a period of 158 nm, using InGaP and GaAs materials, and controlling the growth temperature to prevent thermal deformation and oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electron beam exposure is used to fabricate diffraction grating, then precise control over grating period is achieved, but exposure time becomes excessively long and volume production becomes difficult
Solution Approach 1:
The patent uses holographic exposure to create a latent image of the diffraction grating pattern through interference of laser beams, copying the desired grating structure directly onto the photoresist without requiring sequential electron beam scanning. This enables simultaneous exposure of the entire grating area, dramatically reducing exposure time while maintaining precision through the interference pattern geometry.
2Productivity
If holographic exposure is used to fabricate diffraction grating, then exposure time is reduced, but light scattering losses increase and manufacturing precision deteriorates
Solution Approach 1:
The patent optimizes holographic exposure parameters including laser wavelength, incident angle, and photoresist thickness to achieve precise grating period control. By carefully selecting the interference angle and wavelength, the grating period can be precisely controlled according to the formula Λ = λ/(2 sinθ), while minimizing light scattering losses through proper parameter matching.
3Productivity
If high temperature is used during diffraction grating fabrication, then etching efficiency is improved, but thermal deformation increases
Solution Approach 1:
The patent employs selective etching where the etch process is localized to specific regions defined by the photoresist mask pattern. This allows high-temperature etching to be applied only where needed for efficient material removal, while the mask protects other regions from thermal damage and deformation, maintaining overall grating shape precision.
4Device complexity
If conventional single-layer diffraction grating structure is used, then fabrication is simplified, but light coupling coefficient is reduced
Solution Approach 1:
The patent employs a composite diffraction grating structure consisting of multiple layers with different refractive indices, including a core layer and cladding layers. This composite structure enhances the light coupling coefficient by creating stronger optical confinement and better mode matching, while the layered design allows independent optimization of each layer's properties for overall performance improvement.
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 the fabrication of semiconductor lasers with improved light coupling coefficients and reduced thermal deformation, enhancing the efficiency and reliability of the diffraction grating while maintaining a thin structure and avoiding oxidation, thus addressing the limitations of existing methods.
Implementation Method 1
the photoresist is irradiated with an electron beam to form a striped grating latent image having a period Λ on the photoresist. The electron beam used in the EB exposure is produced by focusing a stream of electrons emitted from an electron gun
Implementation Method 2
the photoresist is irradiated with laser beams from two directions to form a latent image of a holographic pattern. The period Λ of the holographic pattern is Λ=λ/2 sin θ, where θ is the incident angle of the two laser beams and λ is the wavelength
Implementation Method 3
The latent image of the photoresist formed by any of these exposure methods is developed to form a visible image, which is used as resist mask having a grating pattern
Implementation Method 4
Regions in the silicon oxide film that are exposed in the resist mask are etched into a grating pattern by dry etching
Data Source
AI summary
An optical semiconductor device, includes: a plurality of first diffraction grating layers disposed at a spacing from each other along first direction above first semiconductor layer, length of a lower surface of each of a plurality of first diffraction gratings along first direction being longer than a length of an upper surface of first diffraction grating; second diffraction grating layer disposed along first direction above first semiconductor layer, first and second diffraction grating layers being alternately disposed at a spacing from each other, a length of an upper surface of second diffraction grating layer along first direction being longer than the length of a lower surface of second diffraction layer; a diffraction grating including first and second diffraction grating layers; a second semiconductor layer disposed between first and second diffraction grating layers and under second diffraction grating layer; and third semiconductor layer disposed on first and second diffraction grating layers.