Acoustoelectric Methods for the Generation Manipulation and Detection of THz Radiation

Lead Research Organisation: University of Leeds
Department Name: Electronic and Electrical Engineering

Abstract

The conversion of acoustic signals (sound) to electrical signals, and vice-versa, is a technology that has found widespread practical applications. These include, for example: microphones and loudspeakers for sound recording and reproduction at audio frequencies (approx 20 Hz to 20 kHz); transducers for ultrasonic pulse-echo measurement and ultrasonic imaging systems (approx 20 KHz to 100s of MHz); and surface acoustic wave devices for signal processing in mobile communication devices (100s of MHz to a few GHz). The aim of this project is to develop a new technology for conversion between acoustic and electromagnetic (EM) signals, which works at much higher frequencies (10s of GHz to a few THz) and exploits acoustoelectric and piezojunction effects in semiconductor nanostructures and devices.

Acoustoelectric effects in semiconductors are due to the electrons "riding" the acoustic wave as it travels through the crystal. The electrons are effectively dragged along by the sound wave from one electrical contact to the other, giving rise to an electrical current. We have recently obtained experimental evidence for acoustoelectric effect at acoustic wave frequencies up to 100s of GHz in semiconductor nanostructures which points to the feasibility of the proposed project to reach the THz range. The piezojunction effect is a related phenomenon, where the sound wave modulates the electrical conduction across an interface, or junction, between semiconductors such as found in, for example, diodes and transistors. Again, recent experimental evidence obtained by us shows that the piezojunction effect works to very high (THz) frequencies. In the project we will investigate a number of the most promising devices for acoustoelectric applications, and optimise their sensitivity and speed in response to the THz acoustic waves generated by ultrafast laser techniques or saser (sound laser).

Potential applications, which we will explore in this project, include: new and improved methods of generation, manipulation and detection of THZ EM waves, e.g. heterodyne mixing of THz sound with THz EM waves, which have applications is scientific research, medical imaging and security screening; and the generation and detection of nanometre wavelength hypersound, which may be used to extend the established ultrasonics measurement and imaging techniques to the study of materials and structures at the nanoscale.

Publications

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Description This grant has allowed a detailed investigation of the modulation of two dimensional acoustic waves and THz quantum cascade lasers using bulk acoustic waves. Light modulators for THz radiation are a fundamental component of many potential terahertz systems, and are key to transmission of information by a terahertz carrier wave.
Exploitation Route Building new terahertz systems
Sectors Electronics