Contact Information:
e-mail:
phone: (217) 333-4402
fax: (217) 333-5052
207 Roger Adams Lab
MC-712, Box C-3
600 S. Mathews Ave.
Urbana, IL 61801
Research in this group focuses on the control of defect behavior in semiconducting materials to make nanoscale devices of interest in energy, environmental, and microelectronics applications. Despite the harmful sound of “defect,” such species can actually be beneficial for semiconductor properties. For example, controlled substitution of dopant atoms for host atoms in a semiconductor (as “substitutional defects”) is absolutely essential for the operation of microelectronic devices. Our work aims primarily at controlling the behavior of substitutional, interstitial, and vacancy defects within semiconducting solids and on their surfaces. Indeed, “defect engineering” seeks to control the primary kinds of defects in semiconductors as well as their concentrations, spatial distribution, and mobility. We have discovered two new physical mechanisms to accomplish this control that work particularly well at the nanoscale. The mechanisms include saturation of dangling bonds at a surface and photostimulation. Our work employs both experiments and computations to develop this fundamental science base while simultaneously applying the findings to practical applications.
The principles of defect engineering operate in semiconductors such as metal oxides used in catalysts for energy applications. In fuel cells, for example, metals supported on semiconducting oxides such as Pt/Co2O3 and Pd/V2O5 are known to be among the best catalysts for cathodes and anodes, respectively. Noble metals on semiconducting oxides can be used for generating hydrogen from water using sunlight. Active metal particles are often very small – sometimes only a few nanometers in diameter. The activity can be strongly influenced by defects near the semiconductor surface. Thus, we view these systems as nanoscale semiconductor devices whose behavior can be tailored through control of the defects. This approach provides a new way to create novel catalyst structures with improved activity and selectivity. Defect engineering also finds use in environmental catalysis applications. For example, vanadia (V2O5) supported on titania (TiO2) is the best material for selective catalytic reduction of dangerous nitric oxides to nitrogen by ammonia in combustion exhausts. Titania has many existing and potential uses in water cleanup by photocatalysis, as well as in self-cleaning coatings. One factor that limits the efficiency of such catalysts is unwanted defects that destroy the useful photoelectrons. Defect engineering to remove the unwanted defects would permit higher efficiency.
We are also applying our approaches to the formation of pn junctions for advanced transistors in microelectronics. The junctions are created by ion implantation of dopants and subsequent heating. Heating gives the atoms in the structure enough energy to move around so that damage left over from implantation can be healed, and so that more dopant atoms can move into useful sites. The annealing is done with very powerful lamps. However, the annealing also makes the dopant sink deeper and adversely affect device performance. Since nearby surfaces as well as photostimulation are involved, we are employing our two methods of defect engineering to devise new ways to solve this problem.
R. Vaidyanathan, M.Y.L. Jung and E.G. Seebauer, "Mechanism and energetics of self-interstitial formation and diffusion in silicon," Physical Review B, 75, 195209 (2007).
S.H. Yeong, M.P. Srinivasan, B. Colombeau, L. Chan, R. Akkipeddi, C.T.M. Kwok, R. Vaidyanathan and E.G. Seebauer, "Defect engineering by surface chemical state in boron-doped preamorphized silicon," Applied Physics Letters, 91, 102112 (2007).
V. Subramanian, J.U. Choi, E.G. Seebauer and R.I. Masel, "TiO2-Al2O3 as a support for propane partial oxidation over Rh," Catalysis Letters, 113, 13-18 (2007).
X. Zhang, M. Yu, C.T.M. Kwok, R. Vaidyanathan, R.D. Braatz and E.G. Seebauer, "Precursor mechanism for interaction of bulk interstitial atoms with Si(100)," Physical Review B, 74, 235301 (2006).
R. Vaidyanathan, E.G. Seebauer, H. Graoui and M.A. Foad, "Influence of surface adsorption in improving ultrashallow junction formation," Applied Physics Letters, 89, 152114 (2006).
E. G. Seebauer, K.l Dev, M. Y. L. Jung, R. Vaidyanathan, C. T. M. Kwok, J. W. Ager, E. E. Haller, and R. D. Braatz, "Controlling defect concentrations in bulk semiconductors through surface adsorption," Phys. Rev. Lett., 97 055053 (2006).
E.G. Seebauer and M.C. Kratzer, "Charged point defects in semiconductors," Materials Science & Engineering Reviews, 55, 57-149 (2006).
