Development of an epitaxial lift-off technique for II-VI semiconductor heterostructures

II-VI族半导体具有许多不同于III-V族半导体的性质。一个重要的性质是激子结合能，其在II-VI族化合物如ZnSe和CdSe中大得多，并且可以通过适当的限制进一步增加。这意味着在ZnSe和CdSe激子可以在室温下或在高密度下研究，其中可以观察到复合物如双激子。然而，为了研究宽带隙II-VI族化合物中的这些现象，需要更宽带隙的势垒材料。MgS就是这样的材料，并且可以在GaAs上与ZnSe和CdSe组合以低应变生长。MgS不是一种容易生产的材料。这种材料的生长是在Heriot-Watt开创的，目前，我们是全球仅有的三个可以生长这种含MgS结构的实验室之一。我们最近发现MgS还有一个有用的优点，那就是可以用弱酸溶解它，将生长在它上面的结构与下面不需要的衬底分开。这种技术称为外延剥离，是一种非常强大的生成层的方法，然后可以研究或进行进一步处理。例如，这些层可以很容易地被并入光学腔或放置在具有完全不同物理特性的衬底上。不幸的是，这种技术意味着我们不能在相同的结构中使用MgS作为阻挡层。最近，我们发现在MgS中加入少量的锌可以产生一种合金，它具有良好的约束性并能抵抗酸性蚀刻溶液。这种合金有一个大的应变GaAs，但它表明，有其他相关的低应变合金，这将是完全兼容的结构，我们目前growth.In这项研究中，我们的目标是找到最合适的宽带隙合金组合物，我们可以使用它抵抗我们的蚀刻解决方案。然后，我们将展示其在半导体结构中的使用与MgS结合，其中MgS允许我们执行外延剥离，并且新合金抵抗蚀刻并提供限制。

II-VI semiconductors have many properties which are different from their III-V counterparts. One important property is the exciton binding energy which is much larger in II-VI compounds such as ZnSe and CdSe and can be increased still further by suitable confinement. This means that in ZnSe and CdSe excitons can be studied at room temperature or at high densities where complexes such as biexcitons can be observed. However, to study these phenomena in wide bandgap II-VI compounds requires an even wider bandgap barrier material. MgS is such a material and can be grown with low strain on GaAs in combination with ZnSe and CdSe. MgS is not an easy material to produce. The growth of this material was pioneered at Heriot-Watt and currently, we are one of only three labs worldwide where such MgS containing structures can be grown.We recently found that MgS has one other useful advantage, which is that weak acid can be used to dissolve it, separating the structure grown on top of it from the unwanted substrate underneath. This technique, called epitaxial lift-off, is a very powerful method of generating layers which can then be studied or subject to further processing. For example, the layers can easily be incorporated into optical cavities or placed on to a substrate with completely different physical properties.Unfortunately, this technique means that we can not use MgS as a barrier layer in the same structure. Recently, we have recently found that adding a small amount of zinc to MgS creates an alloy which has good confinement and resists the acid etching solution. This alloy has a large strain to GaAs, but it suggests that there are other related low strain alloys which would be entirely compatible with the structures we currently grow.In this study we aim to find the most suitable wide bandgap alloy composition which we can use which resists our etching solution. We will then demonstrate its use in semiconductor structures in combination with MgS, where the MgS allows us to perform epitaxial lift-off and the new alloy resists the etching and gives the confinement.