The following are a few brief areas of research that our lab is interested in and is currently pursuing.
Integration of complex oxides with semiconductors
The combination of the rich functionality and emergent phenomena in complex oxide materials and their heterostructures is very attractive for making new types of device applications. However, it is important that one is able to deposit these functional oxides on semiconductor substrates, particularly silicon, in order for these materials to be technologically useful. We are working on developing processes for combining functional oxides directly on semiconductors for various applications. We work with ferroelectric BaTiO3 or (SrxBa1-x)1Nb2O6, photocatalytic TiO2, high-k LaAlO3, and ferromagnetic LaCoO3 and Sr(Co,Ti)O3 and integrating them on both silicon and germanium substrates, using a combination of both MBE, ALD, and sputtering growth methods.
All-oxide quantum wells and superlattices
The growth of oxide superlattices is now at a level approaching those of the III-V semiconductors. Such quantum wells based on oxides can enable similar optical and resonant tunneling effects that have been observed in semiconductors but with potentially larger/stronger effects. We have recently started looking into the design of all-oxide artificial superlattice tailored to produce specific optical/transport effects.
Strain tuning of electronic properties
By growing highly correlated electron materials on carefully chosen substrates or pseudosubstrates, one can tune the strain in these materials and control the ground state. We have shown that LaCoO3 can be induced to become ferromagnetic when biaxially tensile strained and that there is a spin state disproportionation in the system. In addition to the cobaltates, we are also looking into strain tuning of the magnetic and metal-insulator transition in (La,Eu)NiO3 where it is expected that a similar disproportionation of an electronic degree of freedom will also occur. We are also investigating the effect of strain on the f-electron ferromagnetic semiconductor EuO.
Oxidation and growth mechanisms of oxides on semiconductors
Our ability to have submonolayer control of the deposition process using both physical (MBE) and chemical (ALD) processes, and our ability to dose oxygen with high precision, in combination with in situ RHEED and ARXPS allows us to follow the growth of an oxide, particularly on semiconductor substrates, from initial deposition to post-annealing (with or without oxygen). We can follow the evolution of the chemical state of the various elements and the extent of oxygen diffusion across different layers as the growth or annealing process proceeds. This information can then be used to optimize the growth of specific oxide systems for certain applications, for example by tuning band offsets between oxides.