Thermoelectric figure of merit (ZT) depends on three material properties; electrical conductivity, thermal conductivity,
and Seebeck coefficient. Maximizing ZT simply requires that electrical conductivity and Seebeck coefficient be high to
reduce Joule heating and to increase energy conversion efficiency while thermal conductivity needs to be low to
maintain temperature gradient across a thermoelectric material. Unfortunately these three material properties are closely
correlated each other in homogeneous bulk semiconductors. Recent demonstrations that employ various semiconductor
materials tuned at the nanometer-scale (nanomaterials) have shown great promise in advancing thermoelectrics. Among
a wide range of nanomaterials, we focus on "nanocomposites" in which semimetallic nanostructures are epitaxially
embedded in a ternary compound semiconductor matrix to attempt tuning the three material properties independently.
We demonstrated co-deposition of erbium monoantimonide (ErSb) and In1-xGaxSb or InSb1-yAsy ternary alloy to form
nanometer-scale semimetallic ErSb structures within these ternary alloys "nanocomposite" using low-pressure metal
organic chemical vapor deposition. The grown nanocomposites were structurally and thermoelectrically analyzed to
assess their potential for advanced thermoelectric power generation.
Efficiency of thermoelectric materials is generally discussed in terms of the dimensionless figure-of-merit, ZT
= S2σT/κ, Many researchers have found that it is possible to reduce the lattice thermal conductivity by
incorporating nanostructures (i.e. nanoparticles or heterobarriers) into materials, thereby scattering phonons.
At the same time, it has been theoretically predicted and experimentally demonstrated that barriers can be
used to "filter" the distribution of carriers which contribute to conduction. By doing so, it is possible to
significantly increase the Seebeck coefficient while only modestly decreasing the electrical conductivity. As a
result of this energy-dependent scattering of carriers, the thermoelectric power factor is increased. We present
theoretical and experimental results for metal/semiconductor nanocomposites consisting of metallic rareearth-
group V nanoparticles within III-V semiconductors (e.g. ErAs:InGaAlAs) demonstrating both an
increase in thermoelectric power factor and a decrease in thermal conductivity, resulting in a large figure of
merit. We also discuss metal/semiconductor superlattices made of lattice-matched nitride materials for
electron filtering and the prospects of these materials for efficient thermoelectrics, especially at high
temperatures. Finally, we will discuss both various synthesis techniques for these materials, including the
prospects for bulk growth, and also devices fabricated from these materials.
InP nanowires were grown by metalorganic chemical vapor deposition (MOCVD) on a quartz substrate that was covered
with a layer (100 nm) of non-single crystal hydrogenated silicon (Si:H) demonstrating that single crystalline platforms
are not a requirement for single crystal semiconductor nanowire growth. Scanning electron microscopy (SEM), X-ray
diffraction (XRD), photoluminescence (PL), Raman spectroscopy and Cathode luminescence (CL) were used to
characterize the structural and optical properties of the nanowires. The nanowires grew in random directions with
uniform size distribution and with high density. Two different crystallographic habits were found to grow as has been
reported previously and the suggestion that the differing crystallographic habits are due to distinct wurtzite and zincblende
crystal structures1 is further substantiated by the XRD profile presented in this paper. The XRD profile suggests
that nanowires either having hexagonal-close-packed or face-centered cubic lattice are present. The Raman spectrum
shows peaks associated with transverse optical (TO) and longitudinal optical (LO) branches of InP. The Raman peaks
closely match those of bulk InP. CL of a single InP nanowire was to study the variations in luminescence along the long
axis of the tapered nanowire from the base (~250 nm in diameter) to the tip (~10 nm in diameter), however no
substantial variation in luminescence was observed along the long axis of the nanowires. Microscopic carrier
recombination dynamics of the nanowires will be discussed with the view towards nanowire-based optical sensors.