Photodetector with Internal Gain and Detector Array
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Solution Overview
Problem
Current internal gain photodetectors face limitations in achieving high amplification gains under low bias voltages with a good signal-to-noise ratio, low response time, and wide wavelength detection, particularly for wavelengths up to 20 micrometers, due to issues like limited spectral sensitivity, high dark current, and degradation in performance at high gains.
Innovation Solution
A semiconductor structure with a P-N type junction and specific bias contacts is designed to create preamplification through minority carrier impact ionization, reducing tunneling current and allowing for higher gains without degrading the signal-to-noise ratio, featuring a photon collection zone close to the first bias contact and a P-N junction closer to the second contact, which can operate in both preamplification and avalanche modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional APD diodes are used to achieve high amplification gains, then signal amplification is improved, but signal-to-noise ratio deteriorates and response time increases
Solution Approach 1:
The photodetector is divided into two functional zones: a first zone for impact ionization events that generates charge carriers, and a second zone with a P-N junction for avalanche multiplication. This segmentation allows each zone to perform its specialized function optimally, achieving high gain while maintaining signal-to-noise ratio by separating the carrier generation and amplification processes.
Solution Approach 2:
Different regions of the photodetector are designed with different properties: the first zone has characteristics optimized for impact ionization and carrier generation, while the second zone contains the P-N junction optimized for avalanche multiplication. This local differentiation enables high amplification gain in the second zone without degrading the signal-to-noise ratio generated in the first zone.
2Adaptability or versatility
If Cd x Hg 1-x Te based APD diodes with low energy gap are used to extend wavelength detection, then detectable wavelength range is improved, but tunneling current increases
Solution Approach 1:
The photodetector separates the wavelength detection function (first zone with low energy gap material for broad spectral response) from the amplification function (second zone with P-N junction). This segmentation allows the first zone to detect a wide wavelength range including long wavelengths up to 20 micrometers while the P-N junction in the second zone provides controlled avalanche multiplication without excessive tunneling current.
3Reliability
If photocathode detectors are used to achieve good signal-to-noise ratio, then signal-to-noise ratio is improved, but device size increases and quantum efficiency decreases
Solution Approach 1:
The invention uses semiconductor materials with carefully selected energy gap parameters to achieve both compact size and good signal-to-noise ratio. By optimizing the material composition and P-N junction characteristics, the device achieves high quantum efficiency in a compact form factor, unlike photocathode detectors that require large sizes and achieve less than 50% quantum efficiency.
4Reliability
If EMCCD devices are used to achieve high quantum efficiency, then quantum efficiency is improved, but spectral sensitivity is limited
Solution Approach 1:
The photodetector uses composite semiconductor structures with different material properties in different zones. The first zone uses materials optimized for broad spectral detection including near-infrared wavelengths, while the second zone contains the P-N junction for avalanche multiplication. This composite approach extends spectral sensitivity beyond the 0.9 micrometer cutoff of silicon-based EMCCDs to include near-infrared and longer wavelengths.
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 configuration achieves gains comparable to or exceeding those of conventional APD diodes while minimizing dark current and maintaining a strong signal-to-noise ratio, enabling detection across a broader wavelength range with reduced bias voltages and improved response time.
Implementation Method 1
a semiconductor structure, in which impact ionization events are mainly created by minority carriers
Implementation Method 2
a collection contact arranged in the P-N junction to collect the current in the P-N junction
Data Source
Figure 1~4
Figure 5~7
Figure 8~10
AI summary
The photodetector with internal sheath (10) comprises a semiconductor-structure (12) in which events of impact ionization are created by minority carrier, first and second contacts (16, 18) arranged in the polarization of semiconductor structure, a unit for defining the structure in a semiconductor photon collection area near the first contact of polarization, a mesa type PN junction (20) formed in the semiconductor structure between the two contacts of polarization and near the second contact of polarization, and a collection contact (22). The photodetector with internal sheath (10) comprises a semiconductor-structure (12) in which events of impact ionization are created by minority carrier, first and second contacts (16, 18) arranged in the polarization of semiconductor structure, a unit for defining the structure in a semiconductor photon collection area near the first contact of polarization, a mesa type PN junction (20) formed in the semiconductor structure between the two contacts of polarization and near the second contact of polarization, and a collection contact (22) arranged in the pn junction to collect the current in the P-N junction. The semiconductor structure comprises a first semiconductor layer of a first conductivity type and a PN junction zone of a semiconductor second conductivity type arranged in the first semiconductor layer, and a second semiconductor layer inserted into the first semiconductor layer. The second semiconductor layer has a bandgap smaller than the first layer and same or different conductivity type as the first semiconductor layer with a doping lower than the first semiconductor layer. The unit for defining the area of photon collection includes an opaque plate arranged on or beneath the semiconductor structure and having an opening, and a convergent microlens arranged on or below the semiconductor structure. The semiconductor structure includes a cadmium-mercury-tellurium alloy represented as Cd xHg 1 - xTe, where cadmium has 60% of stoichiometry.