Development of MBE grown CrSe for spintronics applications

电子是具有自旋和电荷的粒子，并且像电荷一样，自旋的取向可以用于存储和传输信息。这引起了自旋电子学的迅速发展。目前，成功的自旋电子器件都是基于包含磁性和非磁性金属交替层的结构，并且迄今为止，在开发成功的包含半导体的自旋电子器件方面存在相当大的问题，这种器件需要磁性材料，该磁性材料可以与半导体形成结，以选择性地注入或去除具有一个特定自旋取向的电子。理想情况下，这种材料应该在室温下工作良好，不与半导体发生化学反应，只注入一个自旋取向。到目前为止，还没有一种材料能同时满足这三个条件。半金属是一类磁性材料，作为潜在的半导体接触材料引起了人们的极大兴趣。在半金属中，两个不同自旋电子的能带具有完全不同的能量，因此费米能量对于一个自旋方向位于导带底部之上，而对于另一个自旋方向位于导带底部之下。对于第一自旋取向，材料表现为金属，而对于另一自旋取向，材料表现出所有典型的半导体特征，例如带隙。最近已经表明，某些过渡金属与元素周期表第V或VI族元素的化合物在锌单晶结构中生长时是半金属的，这也意味着它们可以作为具有更常规半导体的多层结构的一部分生长。然而，所有这些化合物通常不会在这种晶体结构中生长，这意味着它们必须以更高能量的亚稳态形式生长。在本提案中，我们已经确定了这些材料中最有前途的一种，即化合物硒化铬。这具有许多吸引人的特性，应该满足所有三个标准的良好接触材料。尽管如此，锌铬硒从来没有生长过。该原理证明提案的目的是证明CrSe可以通过分子束外延（MBE）在锌单晶结构中生长。结构特性（晶格常数、泊松比等）将在赫瑞瓦特大学进行测量，样品也将提供给马尔堡菲利普大学的Wolfram Heimbrodt教授，他将对这些层的磁性能进行基本评估。如果该提议证明可以用锌尖晶石晶体结构生产CrSe，并且正如预测的那样，薄层在室温以上是铁磁性的，那么随后将产生一个完整的建议，其目的是在一系列自旋电子器件中利用CrSe的性质。

Electrons are particles which have spin as well as charge, and like charge the orientation of the spin can be used to store and transport information. This has given rise to the rapidly developing area of spintronics. Currently the successful spintronic devices are all based on structures which contain alternating layers of magnetic and non-magnetic metals, and to date there have been considerable problems in developing successful spintronic devices containing semiconductors.Such devices require a magnetic material which can form a junction with a semiconductor to selectively either inject or remove electrons with one particular spin orientation. Ideally, the material should work well at room temperature, not react chemically with the semiconductor and only inject one spin orientation. To date there is no material with fulfils all three criteria.Half metals are types of magnetic material which have attracted considerable interest as potential semiconductor contacts. In a half metal, the bands for the two different spin electrons have quite different energies, so that the Fermi energy lies above the bottom of the Conduction Band for one spin orientation, but is below it for the other. For the first spin orientation the material behaves as a metal, while for the other it demonstrates all the typical semiconducting features, such as a bandgap.Recently it has been shown that compounds of certain transition metals with elements from group V or VI of the periodic table are half metallic when grown in the zinc blende crystal structure, which also means they can be grown as part of multilayer structures with more conventional semiconductors. However all of these compounds do not normally grow in this crystal structure which means that they have to be grown in a higher energy, metastable form.In this proposal we have identified one of the most promising of these materials, which is the compound chromium selenide. This has many attractive properties and should satisfy all three criteria for a good contact material.Despite this, zinc blende CrSe has never been grown before. The aim of this proof of principle proposal is to demonstrate that CrSe can be grown in the zinc blende crystal structure by molecular beam epitaxy (MBE). The structural properties (lattice constant, Poisson's ratio, etc) will be measured at Heriot-Watt University and samples will also be provided to Prof. Wolfram Heimbrodt at Philipps Universitaet, Marburg who will provide a basic assessment of the magnetic properties of the layers.If this proposal demonstrates that CrSe can be produced with the zinc blende crystal structure and, as predicted thin layers are ferromagnetic above room temperature, then a subsequent full proposal will then be produced which will aim to exploit the properties of CrSe in a range of spintronic devices.