ULTRA-HIGH-RESOLUTION, ULTRA-SENSITIVE MULTIFUNCTIONAL BALLISTIC NANO SENSORS FOR THE SIMULTANEOUS DETECTION OF MAGNETIC, ELECTRIC AND OPTICAL FIELDS

在宏观长度尺度上，半导体中的载流子可以用扩散输运性质来描述，霍尔效应等传感器概念是适用的。当材料在纳米尺度上制造时，新的特性出现，量子效应占主导地位。在高迁移率材料中，如窄间隙半导体（NGS），当器件长度尺度小于电子平均自由程时，载流子表现出弹道特性。在InSb（和InAs）量子阱结构中，室温迁移率分别超过40,000（和25,000）cm2/Vs，产生的电子平均自由程超过500nm，原则上使用当前的处理技术可以实现。然而，室温下的弹道效应，即使在高迁移率的NGS中仍然难以捉摸。因此，对这一有趣且潜在重要的运输机制没有进行重大的探索和开发。由于目前的资金（EPSRC EP/F067216 - EP/F065922 - 2011年11月结束日期），我们已经取得了重大的理论和实验进展，导致NGS异质结构的室温弹道效应的演示。我们已经证明，在简单的交叉结构中创建准直弹道电子是可能的，这增强了所谓的负弯曲阻力（NBR）。我们还表明，准直NBR传感器的响应度（四个终端器件对扰动场的电阻变化）与器件尺寸成反比。值得注意的是，这意味着随着尺寸的缩小，传感器性能没有明显的损失，这是纳米级电子应用中非常理想的特性。我们新提案的重点是建立在这些可观的实验和理论发展的基础上。我们计划使用NBR几何结构作为自然平台来实现在室温下工作的高灵敏度多功能NGS弹道纳米传感器，该传感器利用器件暴露于磁、电和/或光场时产生的电阻变化。作为这一愿景的一部分，我们计划整合另外两个关键的设备概念，以实现设备的多功能特性并提高灵敏度。首先，我们发现在适当的器件几何结构中，扰动外部场，如光场，可以将载流子从弹道状态转换为扩散状态。其次，适当放置在器件架构内的金属分流，提供低电阻路径，并通过肖特基势垒进入该路径，可通过外部扰动场进行调谐。后一种特性在EXX传感器的扩散装置中发挥了巨大作用，EXX传感器是由我们提议的访问学者斯图尔特·索林（Stuart Solin）教授发明的。除了我们自己的初步研究外，在弹道极限下集成金属分流是一个全新的概念，诸如等离子体效应和热载子效应等方面需要进行研究。到目前为止，我们的成果都是基于InSb异质结构。研究尽可能小的设备的动机，意味着拨款活动将包括探索InAs量子阱设备的性质。InAs提供了与InSb相似的室温平均自由程，但其优点包括总体电阻更低，可以选择更重的掺杂，由于可以忽略侧壁损耗，因此在控制准直方面具有更大的可调性潜力。室温下弹道状态下界面效应的研究是一个几乎完全未开发的领域，由于对高分辨率高灵敏度传感器的应用需求得到了认可，包括生物传感、使用磁珠检测的护理点诊断、信息通信技术和安全，我们的工作是及时的，并且非常适合EPSRC的研究战略领域。

At macroscopic length scales, charge carriers in semiconductors can be described by diffusive transport properties and sensor concepts such as the Hall Effect are applicable. When materials are fabricated at the nanoscale, new properties emerge and quantum effects dominate. In high-mobility materials such as narrow-gap semiconductors (NGS), charge carriers exhibit ballistic properties, when device length scales are smaller than the electron mean free path. In InSb (and InAs) quantum well structures, room-temperature mobilities exceed 40,000 (and 25,000) cm2/Vs, respectively, yielding electron mean free paths in excess of 500nm, which are accessible in principle using current processing technology. Nevertheless, room-temperature ballistic effects, even in high mobility NGS have remained elusive. As a result there has been no significant exploration and exploitation of this interesting and potentially important transport regime. As a result of current funding (EPSRC EP/F067216 - EP/F065922 - end date November 2011) we have made significant theoretical and experimental developments, resulting in the demonstration of room temperature ballistic effects in NGS heterostructures. We have shown that it is possible to create collimated ballistic electrons in a simple cross-structure, which enhances the so called negative bend resistance (NBR). We have also shown that collimated NBR sensor responsivity (the change in four terminal device resistance to the perturbing field) scales with inverse device size. Remarkably, this means that there is no significant loss in sensor performance as the dimensions shrink, a highly desirable property for nanoscale electronics applications.The focus of our new proposal is to build on these considerable experimental and theoretical developments. We plan to use the NBR geometry as a natural platform to realise high sensitivity multifunctional NGS ballistic nanosensors operating at room temperature, which utilise the change in electrical resistance that results when the device is exposed to magnetic, electric and/or optical fields. As part of this vision we plan to integrate two other key device concepts that will enable the multifunctional character of the devices and boost sensitivity. The first is our discovery that in the appropriate device geometry, perturbing external fields, such as optical fields, can convert carriers from the ballistic to the diffusive regime. The second is that a metal shunt appropriately placed within the device architecture, provides a low resistance path and access to that path via a Schottky barrier is tunable via external perturbing fields. This latter property has been used to great effect in diffusive devices known as EXX sensors, which were invented by a coinvestigator and visiting academic on our proposal, Prof Stuart Solin. Apart from our own preliminary investigations, the integration of a metallic shunt in the ballistic limit, is a completely new concept and aspects such as plasmonic effects and hot carrier effects will need to be investigated. Up to this time our achievements are based on InSb heterostructures. The motivation to examine the smallest possible devices, means that the grant activities will include exploration of the properties of InAs quantum well devices. InAs offers similar room temperature mean free paths to InSb, but has attractions including lower overall resistance, the option to be more heavily doped and greater potential for tunability as far as controlling collimation because of negligible side wall depletion.The study of interface effects in the ballistic regime at room temperature is a field almost completely unexplored and because of the recognised demand for high-resolution high-sensitivity sensors for applications spanning biosensing, point of care diagnostics using magnetic bead detection, ICT, and Security, our work is timely and fits well within the EPSRC research strategic areas.