  Like silicon-based semiconductor devices, van der Waals heterostructures will
require integration with high-K oxides. This is needed to achieve suitable
voltage scaling, improved performance as well as allowing for added
functionalities. Unfortunately, commonly used high-k oxide deposition methods
are not directly compatible with 2D materials. Here we demonstrate a method to
embed a multi-functional few nm thick high-k oxide within van der Waals devices
without degrading the properties of the neighbouring 2D materials. This is
achieved by in-situ laser oxidation of embedded few layer HfS2 crystals. The
resultant oxide is found to be in the amorphous phase with a dielectric
constant of k~15 and break-down electric fields in the range of 0.5-0.6 V/nm.
This transformation allows for the creation of a variety of fundamental
nano-electronic and opto-electronic devices including, flexible Schottky
barrier field effect transistors, dual gated graphene transistors as well as
vertical light emitting and detecting tunnelling transistors. Furthermore, upon
dielectric break-down, electrically conductive filaments are formed. This
filamentation process can be used to electrically contact encapsulated
conductive materials. Careful control of the filamentation process also allows
for reversible switching between two resistance states. This allows for the
creation of resistive switching random access memories (ReRAMs). We believe
that this method of embedding a high-k oxide within complex van der Waals
heterostructures could play an important role in future flexible
multi-functional van der Waals devices.
