Multifunctional III-nitride materials

新器械材料：为什么？照明、公共交通、制造业和个人电脑-这些都是我们现代生活的核心。不幸的是，现在，灯泡浪费了我们投入其中的95%的电力，而交通和工业中使用的交流电机和电源可以浪费高达45%，个人电脑中的RAM即使不使用也会浪费数十瓦。鉴于我们对能源的需求不断增加，但化石燃料供应有限，这是一个主要问题！然而，主要的节能可以通过改进两种基本类型的电气设备来实现：发光二极管（LED）和晶体管。特别是，我们需要更高效的绿色LED（与现有的红色和蓝色LED结合产生白色光），我们需要能够在非常高的功率和频率下高效运行而不会在待机时浪费能量的晶体管。这样的设备也可以缩小并适用于超高密度计算机存储器。然而，目前的材料无法达到这些器件所需的性能，因此必须找到更好的材料。电子设备中的材料通常只有一个主要功能。例如，氮化镓在蓝色LED和高功率晶体管中用作半导体。然而，该提案的重点是创造多功能氮化物基材料，用于新的改进设备。目前，一些奇异的材料可以同时作为半导体，铁电体（即它们具有自发的，可逆的电极化）和磁体，但它们中的大多数是不稳定的，难以制造或在室温下不工作。相反，现有的氮化物半导体可以通过添加钪等金属来修改，这会在晶体结构中产生微小的扭曲。这些材料特别令人兴奋，因为扭曲可以产生新的铁电和磁性，没有人认为可以在氮化物中共存。在低金属浓度下，新材料是稳定的，可以发出正确颜色的光，以取代现有的绿色LED中有高度缺陷的有源区。在较高的金属浓度下，扭曲排列起来，整个晶体结构发生变化。这样的材料可以用于晶体管，在那里它们应该产生一个薄的可切换的电子层，提供一个非常低的“开”电阻，而不会在“关”时消耗功率。或者，通过检测这个电子层的存在与否，我们可以拿走晶体管的“源极”和“漏极”，并创建密集的、可堆叠的纳米尺寸器件阵列，这些器件可以提供破纪录的数据存储密度。根据材料的磁和电特性如何相互作用，甚至可以同时存储多位信息。预计这些新材料既坚固又与现有的氮化物加工技术兼容，使其具有很大的实用价值。然而，首先，必须更充分地了解它们的基本特性，以便充分利用它们为未来节能设备提供的迷人的新可能性。这可以通过创建和表征最有前途的材料（从（Sc，In，Ga）N材料系统开始），理解和控制它们的基本属性，并使用这些知识来设计最佳利用这些属性的新节能设备来实现。影响：更好的绿色LED可以帮助我们节省高达80%的照明能源。沿着更高效的大功率晶体管应用于工业、运输和通信，这将大大减少我们对化石燃料的依赖。从长远来看，这种节能显示器和电源还可以与超高密度存储器相结合，为我们提供更小，更快，更轻的计算机，具有巨大的数据存储容量和非常长的电池寿命，几乎惠及社会的每一个部分。

New device materials: why?Lighting, public transport, manufacturing and personal computing - these are central to our modern lives. Unfortunately, right now, light bulbs waste 95% of the electricity we put into them, whereas the AC motors and power supplies used in transport and industry can waste up to 45% and the RAM in personal computers can waste tens of watts even when it isn't used. Given our rising demand for energy but limited fossil fuel supplies, this is a major problem! However, major energy savings can be made by improving just two basic types of electrical device; light-emitting diodes (LEDs) and transistors. In particular, we need much more efficient green LEDs (to be combined with existing red and blue LEDs to produce white light) and we need transistors that can run efficiently at very high powers and frequencies without wasting energy on standby. Such devices could also be shrunk and adapted for use in ultra-high-density computer memory. However, current materials cannot reach the performance needed for these devices, so better materials must be found. What do novel nitrides have to offer? Materials in electronic devices usually have just one main function. For example, gallium nitride works as a semiconductor in blue LEDs and high-power transistors. However, this proposal centres on creating multifunctional nitride-based materials for use in new, improved devices. Currently, some exotic materials can simultaneously act as semiconductors, ferroelectrics (i.e. they have a spontaneous, reversible electric polarization) and as magnets, but most of them are unstable, difficult to manufacture or don't work at room temperature. Instead, existing nitride semiconductors could be modified by adding metals like scandium, which generate tiny distortions in the crystal structure. These materials are particularly exciting because the distortions can produce new ferroelectric and magnetic properties which nobody thought could coexist in the nitrides. At low metal concentrations, the new materials are stable and can emit light of the right colour to replace existing, highly defective active regions in green LEDs. At higher metal concentrations, the distortions line up and the entire crystal structure changes. Such materials could then be used in transistors, where they should produce a thin switchable layer of electrons, giving a very low 'on' resistance without drawing power when 'off'. Alternatively, by detecting the presence or absence of this electron layer, we could take away the transistor 'source' and 'drain' and create dense, stackable arrays of nanometer-sized devices which could provide record-breaking data storage densities. Depending on how the materials' magnetic and electrical properties interact, multiple bits of information might even be stored simultaneously. These new materials are expected to be both robust and compatible with existing nitride processing technology, making them of great practical value. Firstly, however, their fundamental properties must be understood more fully, in order to make the most of the fascinating new possibilities they offer for the energy-efficient devices of the future. This can be done by creating and characterising the most promising materials (starting with the (Sc,In,Ga)N materials system), understanding and controlling their fundamental properties and using this knowledge to design new energy-efficient devices that best exploit these properties. Impact: Better green LEDs could help save up to 80% of the energy we use in lighting. Along with more efficient high-power transistors for industry, transport and communications, this would reduce our dependence on fossil fuels significantly. In the long term, such energy-efficient displays and power supplies could also be combined with ultra-high-density memory to give us smaller, faster, lighter computers with enormous data storage capacities and very long battery lives, benefiting almost every part of society.