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

II-VI型半导体有许多不同于III-V型半导体的特性。一个重要的性质是激子结合能，在II-VI化合物中，如ZnSe和CdSe，激子结合能要大得多，并且可以通过适当的约束进一步提高。这意味着ZnSe和CdSe中的激子可以在室温或高密度下进行研究，在高密度下可以观察到双激子等复合物。然而，要在宽禁带II-VI化合物中研究这些现象，需要更宽的禁带阻挡材料。MgS就是这样一种材料，可以在GaAs与ZnSe和CdSe结合的情况下以低应变生长。MgS不是一种容易生产的材料。这种材料的生长是赫瑞瓦特大学首创的，目前，我们是全球仅有的三个实验室之一，可以生长这种含有mggs结构的实验室。我们最近发现MgS还有一个有用的优势，那就是弱酸可以溶解它，将生长在它上面的结构与下面不需要的底物分开。这种技术被称为外延升空，是一种非常强大的生成层的方法，然后可以研究或进一步处理。例如，这些层可以很容易地集成到光学腔中或放置在具有完全不同物理性质的基板上。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，我们发现在镁合金中加入少量的锌可以产生一种具有良好约束和抗酸蚀溶液的合金。这种合金对砷化镓有很大的应变，但这表明还有其他相关的低应变合金，它们将完全与我们目前生长的结构兼容。在这项研究中，我们的目标是找到最合适的宽禁带合金成分，我们可以使用，以抵抗我们的蚀刻溶液。然后，我们将展示其在与MgS结合的半导体结构中的应用，其中MgS允许我们执行外延提升，而新合金可以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.