Research

The primary research focus of our lab is the growth and characterization of new semiconductor and nanocomposite materials with applications in energy conversion devices, electronics, and optoelectronics. A few of our research areas are briefly described here, but feel free to peruse our Publications or contact Prof. Zide for more detailed information.


Epitaxial Metal/Semiconductor Nanocomposites

Nanocomposites consisting of nanoparticles of rare-earth-group V materials (e.g. ErAs, TbAs) within III-V semiconductors (i.e. (In)GaAs) have properties unlike typical semiconductors; the nanoparticles appear to remain metallic even at this small size, and can drastically impact electrical conductivity, carrier lifetimes, optical absorption, and thermal conductivity of the composite. The rocksalt crystal structure of the rare-earth-group V materials provides a good epitaxial relationship with the zincblende structure of the III-V semiconductors, and allows interfaces which are not highly defective. These materials are useful for applications in tunnel junctions for multijunction solar cells, thermoelectrics, and photoconductive switches for terahertz sources and detectors.

 Work in our lab on the thermoelectric properties of these composites has been funded by Defense Advanced Research Projects Agency - Defense Sciences Office (in a collaboration led by Ali Shakouri at UCSC/Purdue), while efforts to improve our understanding of carrier dynamics in these materials by coupling nanoparticles in InAs quantum dots in collaboration with Matt Doty (UD-MSE) is supported by the National Science Foundation - Division of Materials Research.

In a program sponsored by the Department of Energy - Office of Science through the Early Career Research program, we focused on a scalable and flexible alternative synthesis technique for the exploration of these materials.

 

Dilute Bismuthide Semiconductors

Incorporating a small amount of bismuth into III-V semiconductors causes anomalously narrow bandgaps, which can be modeled using a valence band anticrossing model. We have identified optimized growth conditions for the MBE growth of InGaBiAs on InP platforms and demonstrated bandgap narrowing in good agreement with theoretical predictions. We have recently measured electrical and thermal transport properties in these materials, which are highly promising for applications in thermoelectrics, mid-infrared optoelectronics, terahertz devices, and other (opto)electronic devices.

Work on these materials, with a primary focus on thermoelectrics, has been supported by the Office of Naval Research, partially through the Young Investigator Program.


Thermodynamic Modeling of Doping in Nanoparticles

Nanoparticles, nanowires, and other nanoscale materials have become increasingly important for electronic and optoelectronic devices, but doping of nanoparticles remains a challenge. Previously, kinetics models have been applied to a small subset of these systems, but agreement with experiment is sometimes tenuous. We have developed a simple, thermodynamics-based model in which a minimization of the Gibbs free energy is used to determine (1) whether doping is energetically favorable, (2) whether dopants are likely to sit in the core of a nanoparticle or at the surface, and (3) the concentration of impurities that minimized the free energy of the system. A key strength of this model is that it is quite simple and can be applied to most systems with only a minimum of parameters. It is also easily extensible for more complex systems. We have found that this model, despite its simplicity, is in excellent qualitative agreement — and often good quantitative agreement — with experiment.




Thermoelectric Power Generation in Time Varying Environments

Thermoelectric power generation is valuable for waste heat recovery and energy harvesting, but like any heat engine, it requires a temperature gradient. There are applications where a device might be subjected to high temperatures, but where a spatial gradient is not readily available. By coupling a thermoelectric power generator to objects with drastically different thermal masses and surface areas, variations in temperature over time — whether cyclical or random fluctuations — can be converted to small amounts of electrical energy. This can be useful in applications where small amounts of power are needed over long periods of time, but other energy conversion technologies are not practical.

Work on theoretical modeling of these devices and proof of concept experiments in collaboration with Ajay Prasad (UD-ME) was supported by the University of Delaware Research Foundation through the Strategic Initatives program.