Acoustoelectric Methods for the Generation Manipulation and Detection of THz Radiation

将声信号（声音）转换为电信号，反之亦然，是一项广泛实际应用的技术。这些包括，例如：用于录音和重放音频（约20赫兹至20千赫）的麦克风和扬声器；用于超声脉冲回波测量和超声成像系统的换能器（约20khz至100mhz）；以及用于在移动通信设备中进行信号处理的表面声波装置（100mhz至几GHz）。该项目的目标是开发一种声波和电磁（EM）信号转换的新技术，该技术可以在更高的频率（10ghz到几太赫兹）下工作，并利用半导体纳米结构和器件中的声电和压电结效应。半导体中的声电效应是由于电子在声波穿过晶体时“骑在”声波上。电子被声波有效地从一个电接触点拖到另一个电接触点，从而产生电流。我们最近在半导体纳米结构中获得了声波频率高达100 GHz的声电效应的实验证据，这表明了该项目达到太赫兹范围的可行性。压电结效应是一种相关现象，在这种现象中，声波通过半导体（例如二极管和晶体管）之间的界面或结来调节导电。同样，我们最近获得的实验证据表明，压电结效应工作在非常高（太赫兹）频率。在这个项目中，我们将研究一些最有前途的声电应用设备，并优化它们响应超快激光技术或激光（声激光）产生的太赫兹声波的灵敏度和速度。我们将在本项目中探索的潜在应用包括：太赫兹电磁波产生、操纵和检测的新方法和改进方法，例如太赫兹声音与太赫兹电磁波的外差混合，可用于科学研究、医学成像和安全筛查；纳米波长超声的产生和探测，可将现有的超声测量和成像技术扩展到纳米尺度的材料和结构的研究。

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.