Lattice-Matched Photodiode Structure for Low Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional photodetectors experience stress accumulation and defect formation during epitaxial growth due to large differences in lattice constants between layers, leading to increased dark current and reduced detection accuracy.
Innovation Solution
A stress-balanced photodiode structure is introduced, featuring a substrate, rectifying layer, buffer layer, transition layer, active layer, and absorption layer, where the rectifying layer with InGaP, AlGaAs, and InGaAs layers, along with a connecting layer of GaAs, helps to gradually and continuously match lattice constants, reducing stress and defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a buffer layer is added to provide material compatibility between substrate and quantum well layer, then manufacturing feasibility is improved, but stress accumulation and defect formation increase due to large lattice constant differences
Solution Approach 1:
The buffer layer is divided into multiple sub-layers with progressively changing composition ratios. Each sub-layer has a slightly different lattice constant, creating a gradual transition from the substrate lattice constant to the quantum well layer lattice constant. This segmentation approach reduces stress accumulation at each interface compared to a single abrupt transition layer.
Solution Approach 2:
The composition ratio of the buffer layer is systematically varied across different sub-layers. By changing the aluminum content parameter gradually from the first sub-layer to the last sub-layer, the lattice constant transitions smoothly, reducing stress and preventing defect formation while maintaining manufacturing feasibility.
2Reliability
If multiple buffer layers with different composition ratios are stacked to gradually match lattice constants, then stress accumulation is reduced and defect formation decreases, but device structure becomes more complex
Solution Approach 1:
The buffer layer is divided into a specific number of sub-layers (e.g., 3-5 layers) with progressively changing composition ratios. This segmentation provides sufficient gradient for stress management while avoiding excessive complexity that would arise from too many layers. Each sub-layer serves a specific function in the stress gradient.
Solution Approach 2:
The composition ratio parameter is changed systematically across sub-layers following a designed gradient. This controlled parameter change achieves the necessary lattice constant transition with a manageable number of layers, balancing stress reduction needs against structural complexity.
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
The proposed photodiode design significantly reduces dark current levels and maintains excellent detection responsivity, ensuring improved manufacturing quality and detection accuracy by minimizing stress-induced defects.
Implementation Method 1
the rectifying layer with InGaP, AlGaAs, and InGaAs layers, along with a connecting layer of GaAs, helps to gradually and continuously match lattice constants, reducing stress and defect formation
Implementation Method 2
When electrons in the quantum well layer 13 absorbs enough photo energy to jump energy levels, a corresponding electric signal is generated
Implementation Method 3
The quantum well layer 13 is made of different materials to form a bandgap
Implementation Method 4
the absorption layer 14 absorbs photo energy and transmits the photo energy to the quantum well layer 13
Data Source
AI summary
A photodiode includes a substrate, a rectifying layer, a buffer layer, a transition layer, an active layer, and an absorption layer. The substrate has a base lattice constant. The rectifying layer is formed on the substrate, and includes an InGaP layer, an AlGaAs layer, and an InGaAs layer which are stacked on the substrate in that order. The rectifying layer includes a connecting layer that is made of GaAs directly formed on one of the InGaP layer and the InGaAs layer. The buffer layer is made of GaAs and stacked on the rectifying layer. The transition layer is formed on the buffer layer, and includes a plurality of sub-layers that each has a lattice constant greater than the base constant but smaller than a designated constant. The active layer is formed on the transition layer and has the designated constant. The absorption layer is formed on the active layer.