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

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of Engineering and Physical Science


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.


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Description The aim of the project was to develop the technique of epitaxial lift off and produce a range of materials which would either etch easily or resist the etching solution, and allow the production of complex devices.

These aims were achieved and in addition the group managed to gain an understanding of the mechanisms underlying the etching process and work out how it could be extended to other materials, including MgSe and ZnO.
Exploitation Route Using our understanding of the lift off process, with Nanovation we have started to explore the possibility that gallium nitride devices can be lifted from zinc oxide sacrificial layers.

However the technique is generic and can be applied to any circumstance where a semiconductor needs to be moved from one substrate to another, as long as good electrical contact is not required, examples are thin film optical coatings, filters and modulators. As a result of this work we have produced a wide v
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Energy

Description SUPA Industrial Placement
Amount £53,800 (GBP)
Funding ID B12R1029 
Organisation Heriot-Watt University 
Sector Academic/University
Country United Kingdom
Start 09/2013 
End 03/2014
Description SUPA Industrial Placement (2)
Amount £63,800 (GBP)
Funding ID B13R10454 
Organisation Heriot-Watt University 
Sector Academic/University
Country United Kingdom
Start 02/2014 
End 08/2014