Heterojunction Photodiode Structure for Radiation-Hardened SWIR Detection
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Solution Overview
Problem
Conventional InGaAs photodiodes used in space applications are fragile due to increased dark current and sensitivity to irradiation, particularly in free-space optical communications, where the electric field exacerbates this sensitivity.
Innovation Solution
A method for fabricating photodiodes with the electric carrier collection field placed in a layer least sensitive to radiation, using type-III-V semiconductor materials like InGaAs on an InP substrate, with a stack of semiconductor layers including a p-doped absorption layer, a lightly doped electron collection layer, and a surface barrier layer with a large forbidden band, to reduce irradiation influence on dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional InGaAs photodiodes with internal electric field in the absorbent material are used, then optical detection efficiency is improved, but sensitivity to irradiation increases and dark current increases
Solution Approach 1:
The photodiode structure is segmented into distinct functional layers: an absorption layer for optical detection and a separate collection layer for charge carrier collection. This segmentation allows the electric field to be confined to the collection layer (InP or InAlAs) while the absorption layer (InGaAs) remains field-free, thereby maintaining detection efficiency while reducing irradiation sensitivity and dark current in the InGaAs material.
Solution Approach 2:
Different layers are assigned different doping characteristics and functional properties. The absorption layer is designed with specific optical absorption properties while the collection layer is designed with high electric field characteristics. This local differentiation allows each layer to optimize its function without compromising the other, placing the electric field precisely where it is needed for charge collection while protecting the sensitive InGaAs absorption region from field-induced irradiation damage.
2Adaptability or versatility
If InGaAs materials with narrow forbidden band are used for SWIR detection, then detection capability in the 1.3-1.65 μm wavelength range is improved, but sensitivity to irradiation is exacerbated
Solution Approach 1:
A collection layer made of InP or InAlAs material acts as an intermediary between the InGaAs absorption layer and the external circuit. This intermediary layer carries the electric field and charge collection function, shielding the sensitive InGaAs absorption layer from the harmful effects of the electric field during irradiation, thereby maintaining SWIR detection capability while reducing irradiation sensitivity.
3Ease of operation
If photodiodes operate at non-cryogenic temperatures, then ease of operation is improved, but dark current increases in conventional structures
Solution Approach 1:
The electric field is extracted from the InGaAs absorption layer and relocated to the InP or InAlAs collection layer. This extraction eliminates the primary source of field-induced dark current generation in the InGaAs material, allowing the photodiode to operate at non-cryogenic temperatures with acceptably low dark current levels, thereby improving ease of operation.
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 reduces the sensitivity of photodiodes to irradiation, minimizing dark current and enabling operation in non-cryogenic temperatures, suitable for space applications with improved robustness and bandwidth, particularly in the Short-Wave InfraRed band.
Implementation Method 1
an absorption layer (104) in a p-doped material
Implementation Method 2
a lightly doped electron collection layer (106) having a large forbidden band
Implementation Method 3
electric carrier collection field
Data Source
AI summary
A method for fabricating an optoelectronic component includes at least one photodiode, the steps of the method making it possible to move the electric carrier collection field to the layer least sensitive to radiation, thus reducing the influence of irradiation on the dark current.