Development and Application of Non-Equilibrium Doping in Amorphous Chalcogenides

在20世纪，硅基电子技术的发展彻底改变了世界，成为现代生活背后最普及的技术。预计在21世纪，技术将转向与电子一起使用光(光子)，或取代电子，从而显著提高信息处理的速度和数量，同时也减少了这样做所需的能量。事实证明，实现向全光学“光子”技术的转变是一项复杂的任务，因为电子产品的首选材料硅对光的控制能力有限。在寻找替代材料的过程中，一种被称为无定形硫化物(a-ChGs)的玻璃显示出了非凡的前景，以至于它们被称为“硅的光学等价物”。硫化物是含有一种或多种元素硫、硒或碲作为主要成分的材料。这些材料已经被广泛应用于光伏、存储器(例如DVD)、先进光学设备(例如激光器)以及一些热电发电系统中。人们承认，向全光技术的转变将需要一个中间阶段，在这个阶段中，信息处理是使用混合的光电子系统进行的。这为a-ChGs的发展提供了强有力且令人信服的论据，因为它们可以沉积在Si上以形成一种混合方法，从而将其用作全光学平台。尽管a-ChGs的光学性质可以被控制和修改，但事实证明，在材料制备过程中修改它们的电子性质是极其困难的，这通常涉及高温熔化。在这些条件下，为了改变电子行为而添加到这些材料中的任何杂质都是无效的，因为CHG材料在熔化时能够重新排序，从而抵消了所需的掺杂效应。我们已经成功地开创了一种通过在a-ChGs中引入低于其熔化温度的掺杂剂来改变其性质的方法，从而不允许使用离子注入来重新排列材料。这种掺杂方法允许精确控制引入的杂质类型，并在硅技术中得到广泛应用。作为这项工作的结果，我们展示了以空间局域的方式将大多数电荷载流子类型从空穴(p型)转变为电子(n型)的能力。这一改变步骤的成就使我们能够展示a-ChGs中光学活性pn结的制造，这将成为未来光子技术发展的催化剂。在这个项目中，我们将寻求在原子尺度上全面理解载流子类型反转的过程，并利用这些信息来优化它，以及将要修饰的材料，以增加进一步的功能。我们还将开发所需的先进工程方法，这些方法与通过离子注入a-ChGs引入的掺杂剂的控制和激活有关。总之，这些将使一系列光电子器件的展示成为可能，这些器件展示了构建集成光电子技术所需的关键功能。该方案将巩固英国在硫系化合物非平衡掺杂领域的世界领先地位。通过这种方式，我们将在世界向Beyond CMOS技术过渡的过程中支持这些材料，从而直接为知识经济的持续增长做出贡献。我们将培训下一代科学家和工程师使用最先进的技术，以确保英国保持这一目的所需的专业知识基础，旨在确保这项工作的影响最大化并在可能的情况下加速，并广泛传播结果，包括向本研究的所有利益相关者传达。

In the 20th century, the development of silicon-based electronics revolutionised the world, becoming the most pervasive technology behind modern-day life. In the 21st century, it is envisaged that technology will move to the use of light (photons) together with, or in place of, electrons, providing a dramatic increase in the speed and quantity of information processing whilst also reducing the energy required to do so. Making this transition to an all optical 'photonic' technology has proved to be a complex task, as the material of choice for electronics, silicon, is limited in its ability to control light. In the search for alternative materials, a class of glasses called amorphous chalcogenides (a-ChGs) have shown remarkable promise, to the point where they have been referred to as the 'optical equivalent of silicon'. Chalcogenides are materials which contain one or more of the elements sulfur, selenium or tellurium as a major constituent. These materials are already widely used in applications such as photovoltaics, memory (e.g. DVDs), advanced optical devices (e.g. lasers), and in some thermoelectric generation systems. It is accepted that the move to all-optical technologies will require an intermediate stage where information processing is undertaken using a hybrid 'optoelectronic' system. This provides a strong and compelling argument for the development of a-ChGs, as they can be deposited on Si to form a hybrid approach en-route to their use as an all-optical platform.Whilst the optical properties of a-ChGs may be controlled and modified it has proved to be extremely difficult to modify their electronic properties during the material preparation, which has typically involved melting at high temperatures. Any impurities that are added to these materials in order to change the electronic behaviour are ineffective under these conditions due to the ability of the ChG material to reorder itself when melted, and so negate the desired doping effect. We have successfully pioneered a method to modify their properties by introducing dopants into a-ChGs below their melting temperature, thus not allowing the material to reorder, using ion-implantation. This method of doping allows precise control of the type of impurity introduced and is widely used in silicon technologies. As a result of this work, we have demonstrated the ability to reverse the majority charge carrier type from holes (p-type) to electrons (n-type) in a spatially localised way. This step-changing achievement enabled us to demonstrate the fabrication of optically active pn-junctions in a-ChGs, which will act as the enabling catalyst for the development of future photonic technologies.In this project we will seek to develop a full understanding of the process of carrier-type reversal on the atomic scale, and use this information to optimize it, and the materials that are to be modified, so as to add further functionality. We will also develop the required advanced engineering methods which relate to the control and activation of dopants introduced using ion-implantation into a-ChGs. Together, these will enable the demonstration of a series of optoelectronic devices demonstrating the key functionalities required to build an integrated optoelectronic technology. This programme will consolidate the position of the UK as the world leader in the field of non-equilibrium doping of chalcogenides. We will, in this way, champion these materials in the world's transition to beyond CMOS technology and therefore directly contribute to the continuing growth of the knowledge economy. We will train the next generation of scientists and engineers in state-of-the-art techniques to ensure that the UK maintains the expertise base required for this purpose, aim to ensure that the impact of this work is maximised and accelerated where possible, and communicate the results widely, including to all stakeholders in this research.