3D Photoconductive Transducer for Higher Terahertz Conversion
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Solution Overview
Problem
Existing terahertz sources face challenges with low conversion efficiency, making them unsuitable for applications requiring high terahertz power or operation in cryogenic environments.
Innovation Solution
A photoconductive transducer with a three-dimensional structure comprising a layer of resist with embedded nano-columns between two planar electrodes, optimized for high laser absorption and charge carrier collection efficiency through plasmonic and photonic effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional photoconductive switches are used, then the device can generate terahertz radiation or electrical pulses, but the conversion efficiency from optical power to terahertz power is low
Solution Approach 1:
The patent transitions from conventional planar photoconductive switches to a three-dimensional structure consisting of a semiconductor substrate with vertically grown nano-columns (nanopillars) and metal contacts positioned at their tips. This vertical architecture increases the interaction volume between incident laser light and the photoconductive material, enhancing both light absorption and charge carrier generation efficiency, thereby improving optical-to-terahertz conversion efficiency while maintaining compact device footprint.
Solution Approach 2:
The device employs a composite structure integrating semiconductor nano-columns (e.g., GaAs, InGaAs) with metallic contact materials (e.g., gold, aluminum) and dielectric layers. This composite architecture combines the high photo-response of semiconductors with the excellent electrical conductivity of metals and the optical properties of dielectrics, optimizing both light absorption and charge collection efficiency to achieve high conversion efficiency.
2Ease of manufacture
If conventional planar photoconductive structures are used, then the device structure is simple, but the laser absorption efficiency and charge carrier collection efficiency are low
Solution Approach 1:
The invention introduces vertical nano-columns grown on a planar substrate, transforming the two-dimensional planar structure into a three-dimensional architecture. This vertical configuration increases the effective absorption path length for incident laser light without significantly increasing the device footprint, thereby improving laser absorption efficiency while maintaining manufacturing simplicity through standard semiconductor fabrication techniques.
Solution Approach 2:
The semiconductor layer is segmented into multiple vertically oriented nano-columns (nanopillars) with typical diameters of 50-200 nm and heights of 1-10 μm. This segmentation increases the surface area and light-matter interaction volume, enhancing absorption efficiency. The segmented structure also facilitates efficient charge carrier collection by providing multiple extraction pathways to the metal contacts positioned at the nanopillar tips.
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
The solution achieves significantly improved conversion efficiency, exceeding current transducers by a factor of 10, while enabling operation as both a terahertz emitter and receiver, suitable for a wide range of applications including security, detection, and quantum technologies.
Implementation Method 1
The light provided by the laser source is absorbed by a semiconducting material, such as gallium arsenide (GaAs) or indium gallium arsenide (InGaAs). By means of optical absorption, charge carriers are generated in the semiconductor
Implementation Method 2
This photoconductive assembly is made such as to improve the overall efficiency of the photoconductor device by increasing the laser absorption efficiency in the photo-absorbing regions of the semiconductor substrate through plasmonic resonances
Data Source
AI summary
A photoconductive transducer intended to generate or detect waves in the terahertz frequency domain or in the picosecond pulse domain is provided. The transducer comprises a three-dimensional structure that includes, in this order, a first planar electrode, an array of nano-columns embedded in a layer of resist and a second planar electrode parallel to the first planar electrode. The design of the transducer increases the optical-to-terahertz conversion efficiency by means of photonic and plasmonic resonances and by means of high and homogeneous electric fields. The height of the nano-columns as well as the thickness of the resist range between 100 nanometres and 400 nanometres. The width of the nano-columns is between 100 nanometres and 400 nanometres, the distance between two adjacent nano-columns is between 300 nanometres and 500 nanometres, the nano-columns are made of a III-V semiconductor. The second electrode is transparent, so as to allow the transmission of a laser source towards the photo-absorbing nano-columns.