Delta-Doped Silicon Imaging Arrays for Quantum Efficiency Stability
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Solution Overview
Problem
Existing semiconductor devices face challenges with surface passivation, particularly in back-illuminated detectors, due to inadequate surface passivation technologies leading to reduced quantum efficiency and stability, especially under exposure to deep ultraviolet light and ionizing radiation.
Innovation Solution
The implementation of delta-doping using molecular beam epitaxy to create a sharply peaked dopant profile near the surface, effectively isolating minority carriers from surface defects through quantum exclusion, thereby stabilizing electronic properties and eliminating quantum efficiency hysteresis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional surface passivation is used in back-illuminated detectors, then manufacturing is simpler, but quantum efficiency is reduced and stability is poor under deep ultraviolet light and ionizing radiation
Solution Approach 1:
The patent applies local quality by creating a highly doped delta-layer only in the near-surface region (within 10 nm of the surface) rather than uniformly doping the entire substrate. This localized high-concentration doping zone provides enhanced surface passivation and quantum exclusion effects precisely where needed to improve stability under UV and radiation exposure, while maintaining simpler bulk material properties.
Solution Approach 2:
The patent changes the doping concentration parameter from conventional uniform doping to a sharply peaked delta-function profile with concentrations reaching 10^20-10^21 atoms/cm³ in the delta-layer. This extreme parameter change creates a strong built-in electric field that provides quantum exclusion, preventing carrier injection into surface states and thereby improving device stability and eliminating hysteresis.
2Reliability
If delta-doping with molecular beam epitaxy is implemented, then quantum efficiency and stability are improved, but manufacturing complexity and processing difficulty increase
Solution Approach 1:
The patent replaces conventional mechanical/thermal doping methods (such as ion implantation or thermal diffusion) with molecular beam epitaxy (MBE). MBE is a vapor-phase deposition technique that allows precise control of dopant placement at the atomic level, enabling the creation of sharp delta-doping profiles that are difficult to achieve with traditional methods. This substitution improves manufacturing precision despite requiring specialized equipment.
Solution Approach 2:
The patent performs preliminary action by pre-characterizing and optimizing the MBE growth parameters, dopant source configurations, and temperature profiles before full production. The method includes preliminary steps of substrate preparation, in-situ cleaning, and controlled doping sequence planning to ensure reproducible delta-layer formation. This preliminary optimization reduces processing difficulty and improves ease of manufacture for subsequent production runs.
3Adaptability or versatility
If substrate thinning and surface passivation are performed for back-illumination, then quantum efficiency across broad spectral range is improved, but additional processing steps increase manufacturing complexity
Solution Approach 1:
The patent merges the substrate thinning process with the delta-doping process by performing both operations in-situ within the molecular beam epitaxy chamber. The substrate is thinned to the desired thickness, and the delta-doped passivation layer is deposited immediately afterward without breaking vacuum or transferring the substrate to another chamber. This merging of operations maintains spectral range coverage while improving fabrication throughput by eliminating intermediate handling steps.
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 achieves high and stable quantum efficiency across a broad spectral range, enhances device stability, and reduces dark current, making it suitable for applications in imaging detectors and solar cells.
Implementation Method 1
The implementation of delta-doping using molecular beam epitaxy to create a sharply peaked dopant profile near the surface
Implementation Method 2
effectively isolating minority carriers from surface defects through quantum exclusion
Implementation Method 3
abrupt doping profile situated adjacent at least one of the first surface and the second surface, the abrupt profile having a dopant concentration at least 10^20 cm^-3 and a dopant gradient at least one decade per nm
Data Source
AI summary
Systems and methods for producing high quantum efficiency silicon devices. A silicon MBE has a preparation chamber that provides for cleaning silicon surfaces using an oxygen plasma to remove impurities and a gaseous (dry) NH3+NF3 room temperature oxide removal process that leaves the silicon surface hydrogen terminated. Silicon wafers up to 8 inches in diameter have devices that can be fabricated using the cleaning procedures and MBE processing, including delta doping.