Quasi Van der Waals Epitaxy of Cadmium Telluride on 2D Materials

Cadmium teluride is a key material for many technologies, such as energy production or infrared sensing, which makes the growth of free standing (strain free) layers of CdTe of particular interest. In 2017, Kim et al demonstrated that it is possible to guide the growth of a material through one or few monolayers of 2D material, given that the polarity of the substrate below the 2D material is strong enough. This technique, called “remote epitaxy”, has been applied successfully to a wide range of III-V / 2D systems, such as the epitaxial growth of GaN on hBN / GaN substrate, or GaAs on Graphene / GaAs substrate. Epitaxially grown layers are then easily transferred and the 2D coated substrate can be re-used for future growths. Despite this great success with III-V materials, remote epitaxy of II-VI semiconductors hasn’t been studied much. From a purely theoretical point of view, CdTe with its higher ionicity than GaAs or GaN should be a good candidate for remote epitaxy. However, a transfer step is required to obtain 2D coated substrates, with its lot of difficulties (polymeric contamination, degradation of the 2D surface, oxidation of the substrate…), whereas high quality surface and interface are required to perform remote epitaxy.<br/><br/>Another approach to bypass the need of 2D material transfer would be to perform epitaxy on a reconstructed passivated surface. It has been proven recently (Jovanovic et al, 2020) that sapphire could act as a quasi van der Waals substrate for such a growth of CdTe via the in-situ formation of a monolayer of tellurium at the interface. In such a case, the substrate surface, free from dangling bonds, allows for an easy transfer of the epitaxially grown CdTe membrane. But, unlike with “remote epitaxy”, growth is not seeded by the polar substrate, and one can ask what is the impact on the crystalline quality of the epilayer?<br/><br/>In this communication, we will present the results of MBE grown CdTe film on both sapphire and graphene wet-transferred onto CdZnTe. The crystalline quality of the grown CdTe film is discussed based on SEM, AFM and X-ray diffraction. Graphene quality is checked out prior and after epitaxy based upon Raman spectroscopy. Additional XPS analysis were performed to evaluate substrate oxidation and graphene cleanliness. Results of CdTe layer removal and manipulation will also be presented.