InGaP Betavoltaic Device Dark Current Reduction
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Solution Overview
Problem
Tritium betavoltaic batteries face inefficiencies due to high dark current in semiconductor materials, low energy conversion from Tritium beta emissions, and challenges in hermetically sealing the battery without Tritium exposure, limiting their commercialization and application in low-power devices.
Innovation Solution
The use of Indium Gallium Phosphide (InGaP) homojunction semiconductor devices with a Tritiated metal hydride source, combined with a novel device structure featuring a lattice-matched InAlP window layer and a thin GaAs cap layer, reduces dark current and enhances efficiency, and a hermetic sealing method using low-temperature processes to prevent Tritium leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polycrystalline or amorphous semiconductor based betavoltaic batteries are used, then manufacturing cost is reduced and large surface areas can be produced, but conversion efficiency drops to much less than 1% due to high dark current
Solution Approach 1:
The patent changes the fundamental material parameter from polycrystalline/amorphous semiconductor to single crystal semiconductor, which fundamentally alters the electrical properties by eliminating grain boundaries and reducing defect density. This parameter change reduces dark current by several orders of magnitude while maintaining manufacturability through established single crystal growth techniques
Solution Approach 2:
The patent introduces a heterostructure with spatially varying material composition: a single crystal semiconductor substrate with a specific bandgap is combined with a distinct radioisotope layer. This local quality differentiation optimizes each layer's function - the substrate provides low dark current and the radioisotope layer provides high specific activity beta emission
2Reliability
If single crystal semiconductor devices with Tritium source are used, then carrier lifetime increases and dark current decreases, but efficiency remains limited to around 1-5% with existing homojunction structures
Solution Approach 1:
The patent changes the semiconductor material parameter by selecting a substrate with a larger bandgap energy than previous homojunction designs. This parameter change enables operation at higher temperatures and reduces thermal generation of carriers, thereby reducing dark current and improving the signal-to-noise ratio for beta particle detection
Solution Approach 2:
The patent creates a composite structure combining a single crystal semiconductor substrate with a radioisotope layer (such as Tritium incorporated in metal hydride or polymer matrix). This composite material approach allows optimization of each component - the semiconductor provides charge collection and the radioisotope provides beta emission - achieving synergistic improvement in overall device efficiency
3Power
If high energy beta emitting radioisotopes are used to achieve reasonable power levels, then power output increases, but radiation safety concerns increase and semiconductor destruction risk increases
Solution Approach 1:
The patent concentrates the radioactive material in a thin layer localized at or near the semiconductor surface, rather than distributing it throughout the bulk. This local concentration achieves high specific activity and power density while limiting the volume of radioactive material, thereby reducing overall radiation exposure risk and enabling safer operation
Solution Approach 2:
The patent changes the radioisotope selection parameter by choosing isotopes with appropriate half-lives and beta energies that balance power output with safety. The single crystal semiconductor's superior radiation hardness also changes the system's tolerance parameter, allowing use of higher activity isotopes without immediate device failure
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 an efficiency of 7.5% or higher in converting Tritium beta flux to electrical power, with a long-term lifespan suitable for low-power applications and safe handling, overcoming previous inefficiencies and safety concerns.
Implementation Method 1
The direct conversion of radioisotope beta (electron) emissions into usable electrical power via beta emissions directly impinging on a semiconductor was first proposed in the 1950's. These devices are known as Direct Conversion Semiconductor Devices, Beta Cells, Betavoltaic Devices, Betavoltaic Batteries
Implementation Method 2
a novel device structure featuring a lattice-matched InAlP window layer and a thin GaAs cap layer, reduces dark current and enhances efficiency
Implementation Method 3
a hermetic sealing method using low-temperature processes to prevent Tritium leakage
Data Source
AI summary
A multilayer device for producing electricity. The device comprising a betavoltaic source layer for generating beta particles, and at least three semiconductor layers each having a bandgap substantially similar to a band gap of the other layers, the at least three layers comprising a doped top layer, an undoped intermediate layer and a doped bottom layer, wherein the top and the bottom layers are doped with opposite-type dopants, and wherein the top layer is closer to the betavoltaic source layer than the bottom layer.