Semiconductor Optical Device Surface Flattening for Crystal Quality
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Solution Overview
Problem
The concavo-convex shape formed after burying growth in low mesa structures on p-type substrates poses challenges in maintaining crystal quality and device characteristics, leading to degraded fabrication yield and reproducibility due to lattice mismatch and strain between over-cladding and contact layers.
Innovation Solution
Regrowing an n-type over-cladding layer with a semiconductor crystal doped with selenium (Se) to flatten the concavo-convex shape, with a doping concentration of Se equal to or higher than 5×10^18 cm^-3, and using a semi-insulating semiconductor crystal doped with Ru as a current-blocking layer to prevent inter-diffusion and enhance crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low mesa structure is used to reduce device resistance and improve light output power efficiency, then the current-blocking performance is improved, but the surface becomes concavo-convex after burying growth which degrades crystal quality
Solution Approach 1:
The patent applies preliminary action by performing surface flattening treatment (chemical mechanical polishing or epitaxial growth) on the concavo-convex surface before growing the contact layer. This preliminary flattening prevents the transmission of surface irregularities to the contact layer, thereby maintaining high crystal quality while preserving the low mesa structure's current-blocking performance.
2Reliability
If the burying layer thickness is increased to improve current-blocking, then the current-blocking performance is improved, but the surface irregularity becomes more severe
Solution Approach 1:
The patent converts the harmful surface irregularity caused by thick burying layer growth into a beneficial situation by applying surface flattening treatment. The chemical mechanical polishing or epitaxial growth process transforms the concavo-convex surface into a flat surface, allowing thick burying layers to be used for current-blocking without compromising subsequent layer quality.
3Device complexity
If direct modulation is used to simplify the device structure, then the device complexity is reduced, but the modulation speed is limited by device capacitance
Solution Approach 1:
The patent applies parameter changes by optimizing the device structure parameters (low mesa height, flattened surface) to reduce device capacitance. The surface flattening treatment enables better interface quality and lower capacitance, thereby increasing the relaxation oscillation frequency and modulation speed while maintaining the simplicity of direct modulation.
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 flattens the surface irregularities, improves crystal quality, and enhances device characteristics, fabrication yield, and run-to-run reproducibility, while reducing device capacitance and increasing light output power efficiency, particularly in directly modulated semiconductor lasers.
Implementation Method 1
an n-type over-cladding layer and an n-type contact layer are regrown on the current-blocking layer and the stacked body
Data Source
AI summary
In order to provide excellent device characteristics and enhance fabrication yield and run-to-run reproducibility in a buried device structure using a low mesa on a p-type substrate, a cross sectional configuration before growth of a contact layer of a device, i.e., after growth of an over-cladding layer is flattened so as not to cause a problem in crystal quality of the contact layer. A mesa-stripe stacked body including at least a p-type cladding layer (2), an active layer (4) and an n-type cladding layer (6) is formed on a p-type semiconductor substrate (1), a current-blocking layer (8) is buried in both sides of the stacked body, and an n-type over-cladding layer (9) and an n-type contact layer (10) are disposed on the current-blocking layer (8) and the stacked body. The n-type over-cladding layer (9) is made of a semiconductor crystal having a property for flattening a concavo-convex shape of upper surfaces of the current-blocking layer (8) and the stacked body.