Fabrication of single layer MoS2 on smoothness-enhanced HfO2/Al2O3/HfO2 multilayer

Abstract

Recently, two-dimensional (2D) semiconducting transition metal dichalcogenide (TMD) such as molybdenum disulfide (MoS2) has received considerable attention due to its direct bandgap and unique structure as well as remarkable chemical and physical properties. And with wide-ranging potential applications in nanoelectronics, energy harvesting and optoelectonic devices. However, growth of high-quality and smoothness monolayer is still challenging, because parameters determining growth mechanism are not completely clear. Such as MoS2 is grown at high temperature on dielectric substrates such as HfO2 films, it is inevitable for the substrates layer to be crystallized and resulted in a rough surface. In order to solve this problem, in this test, the process of depositing HfO2 film is used by ALD. The material of Al2O3 was added to the middle of films to test whether or not the surface roughness can be reduced. The reason of ALD is used to deposit HfO2 and Al2O3 is that has a series of advantages such as large area deposition and can easily to controlled deposition thickness. The reason of MoS2 is deposited by CVD is that the deposited film has a series of advantages such as high quality and high density. After the preparation of the samples, a series of experimental analyzes were carried out on the variation of the layer number of MoS2 deposited with the change of HfO2 surface roughness. After the experimental analysis of AFM, XRD, Contact angle, XPS, Raman and TEM of HfO2, HAH and HAHAH, the following conclusions were drawn. With the increase of the HfO2 film thickness, the surface roughness of the film also increases, and the contact angle of the surface gradually increases, resulting in the gradual decrease of the surface energy, which eventually leads to the deposition of MoS2 on the surface of the HfO2 film. However, due to the addition of Al2O3 layer in the structure of HAH, the Al2O3 effectively prevented the film HfO2 crystallization occurs, resulting in its surface roughness has been greatly improved, and ultimately lead to the monolayer MoS2 can be deposited on the thicker HfO2 film.