(1) Interface Structure and Properties
We are engaged in studies of interfaces that form between deposited metal oxides and various high-quality covalent
semiconductor crystals, including Si, Ge, InGaAs and GaN. Most of this work is motivated by the continued dimensional
scaling of field effect transistors, which prompts interest in new high permittivity dielectric materials and new
semiconductors for the transistor channel. Making interfaces with low areal densities of electronic carrier traps is
essential for efficient operation of such devices. Our group studies the role of deposition conditions, process
chemistry, post-deposition annealing on the stability of these oxide/semiconductor interfaces, and the defects they
form. We also investigate methods for protecting semiconductor surfaces during metal oxide deposition and for post-deposition
passivation of interface defects.
(2) Applications of Atomic Layer Deposition
Atomic layer deposition (ALD), a method of surface adsorption-limited chemical vapor deposition, is renowned for
its ability to deposit ultra-thin and pin-hole free films on a wide variety of substrates. We are investigating
applications of ALD in solid oxide fuel cell membranes (e.g. Y2O3-ZrO2 alloy films), ultra-high permittivity dielectrics
(e.g. SrTiO3 multi-cation oxides), and in protection of semiconductors from harsh electrochemical environments
(e.g. TiO2 on n-Si photoanodes for solar water splitting). An important theme in this work is to exploit and investigate
possible changes in the functional properties of these oxide layers as their thicknesses
reach nanoscopic dimensions.
(3) Nanoscale Crystal Growth
We are engaged in studies of nanoscale crystal growth, with particular attention give to Group IV nanowires (NWs), such as Ge NWs and Ge-core/Si-shell NWs.
These unique, molecular-scale structures exhibit fascinating electronic and photonic properties, and can be
synthesized under conditions that are compatible with silicon device fabrication. Our research focuses on deep
sub-eutectic vapor-liquid-solid (VLS) growth of Ge nanowires, the mechanisms and inhibition of misfit strain relaxation
in large-mismatch Ge-core/Si shell nanowires, and kinking during VLS growth of NWs. In collaboration with others,
we use photoluminescence and time-resolved reflectivity measurements to probe the effects of nanowire
diameter, strain and surface defect passivation on electronic structure.