Graded Barrier nBn Infrared Detectors for Dark Current Reduction
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Solution Overview
Problem
The existing nBn infrared detectors are limited to specific infrared wavelengths due to valence band alignment constraints, which impede minority carrier transport and degrade performance in terms of dark current reduction and operating temperature.
Innovation Solution
The introduction of a concentration gradient in the barrier layer and the use of a chirped strained layer superlattice in the absorption layer allows for better valence band matching and alignment, facilitating minority carrier transport and reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If valence band alignment is maintained in heterojunctions, then conduction band offset is maximized for blocking majority carriers, but minority carrier transport is impeded and dark current increases
Solution Approach 1:
The patent applies local quality by creating a graded barrier layer where the bandgap and composition vary spatially. The barrier layer transitions from a composition matching the absorption layer at one interface to a different composition at the other interface, allowing optimized local properties at each heterojunction while maintaining overall device performance.
Solution Approach 2:
The patent changes the bandgap parameter across the barrier layer by varying the alloy composition (e.g., InAsSb grading from x=0 at the absorption layer interface to x=0.5 at the contact layer interface). This parameter change enables simultaneous optimization of majority carrier blocking and minority carrier transport by creating favorable band alignment at each interface.
2Reliability
If conventional nBn detector structure is used, then performance is optimized at specific infrared wavelengths, but adaptability to broader wavelength ranges is limited
Solution Approach 1:
The graded barrier layer structure provides universal applicability across multiple infrared wavelengths. By adjusting the grading profile and composition range, the same basic device structure can be optimized for different wavelength regions (e.g., 3.4μm, 4.4μm, and intermediate wavelengths), making the detector design universally applicable rather than wavelength-specific.
Solution Approach 2:
The patent introduces dynamic adaptability through the graded composition profile, which can be tailored to match different absorption layer materials and operating wavelengths. The gradual transition in bandgap allows the device to dynamically adapt its band alignment characteristics to optimize performance for specific wavelength regions while maintaining the ability to be reconfigured for other 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 approach enables nBn detectors to operate effectively across a broader range of infrared wavelengths with reduced dark current and higher operating temperatures, improving performance and flexibility.
Implementation Method 1
the potential height of the barrier layer is such that there is negligible thermal excitation of majority carriers over it
Implementation Method 2
The barrier layer is thick enough so that there is negligible electronic tunneling through it
Implementation Method 3
The heterojunctions between the barrier layer and the two n-type layers are such that all of the bandgap difference appears in the conduction band offsets. That is, there is essentially zero offset in the valence band.
Implementation Method 4
Pictorially illustrated in FIG. 1 is the generation of a hole-electron pair comprising hole 110 and electron 112 due to the absorption of a photon
Implementation Method 5
the generation of a hole-electron pair comprising hole 110 and electron 112 due to the absorption of a photon
Implementation Method 6
The barrier layer may comprise InAsSb and the concentration of Sb may increase in a direction from the absorption layer toward the contact layer
Implementation Method 7
The absorption layer may comprise a chirped strained layer superlattice of InAs and GaSb
Implementation Method 8
enables nBn detectors to operate effectively across a broader range of infrared wavelengths
Data Source
AI summary
An nBn detector is described where for some embodiments the barrier layer has a concentration gradient, for some embodiments the absorption layer has a concentration gradient, and for some embodiments the absorption layer is a chirped strained layer super lattice. The use of a graded barrier or absorption layer, or the use of a chirped strained layer super lattice for the absorption layer, allows for design of the energy bands so that the valence band may be aligned across the device. Other embodiments are described and claimed.