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

II-VI半导体具有许多不同于III-V半导体的特性。一个重要的性质是激子结合能，它在II-VI类化合物中要大得多，如ZnSe和CdSe，并且可以通过适当的限制进一步增加。这意味着，在锌硒和镉硒中，激子可以在室温或高密度下研究，在那里可以观察到像双激子这样的络合物。然而，要研究宽带隙II-VI化合物中的这些现象，需要一种更宽的带隙势垒材料。MgS就是这样一种材料，它可以在GaAs衬底上以低应变生长，并与ZnSe和CdSe配合使用。MGS不是一种容易生产的材料。这种材料的生长是在Heriot-Watt率先进行的，目前，我们是世界上仅有的三个可以生长这种含有MGS结构的实验室之一。我们最近发现MGS还有另一个有用的优点，那就是可以用弱酸来溶解它，将生长在它上面的结构与下面不需要的衬底分开。这种技术被称为外延剥离，是一种非常强大的产生层的方法，然后可以进行研究或进行进一步的加工。例如，这些层可以很容易地合并到光学腔中或放置到具有完全不同物理性质的衬底上。不幸的是，这种技术意味着我们不能在同一结构中使用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具有良好的约束性和耐酸蚀溶液的合金。这种合金对GaAs有很大的应变，但这表明还有其他相关的低应变合金可以与我们目前生长的结构完全兼容。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，我们可以使用它来抵抗我们的腐蚀溶液。然后，我们将结合MGS演示它在半导体结构中的应用，在MGS中，MGS允许我们执行外延剥离，而新合金抵抗腐蚀并提供限制。

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.