Research Goal: We seek to measure and understand both self- and dopant diffusion in strained, relaxed, and ion implanted Ge and SiGe, utilizing isotopically-controlled structures grown by molecular beam epitaxy (MBE). Diffusion coefficients and mechanisms are determined by continuum theory modeling. Background: Diffusion is a fundamental physical phenomenon resulting from the random motion of atoms. Diffusion of impurities in semiconductor materials is mostly assisted by the presence of vacancies and/or self-interstitials and occurs at rather high temperatures. Studying diffusion is often the most direct way to understand point defects at high temperature. Although much is known about interactions between impurities and point defects in silicon, such knowledge is very limited for SiGe and Ge. Diffusion in Isotopically Controlled Silicon-Germanium Alloys Eugene E. Haller, University of California, Berkeley, DMR Si substrate Cap layer 100 nm natural Si layer Above: Secondary Ion Mass Spectroscopy has been used to determine the diffusion profiles of Si and Ge isotopes as well as arsenic in Si 0.95 Ge The arsenic diffusion profile in Si, annealed under the same conditions as in Si 0.95 Ge 0.05 (13 hrs at 1000 o C), is also included for comparison. As can be observed, arsenic diffuses slightly faster in SiGe than in Si, a typical behavior among common dopants. Careful modeling of the profiles of Si and Ge isotopes will yield important information regarding diffusion mechanisms of arsenic in SiGe. Left: As diffusion coefficients as a function of inverse temperature in an Arrhenius plot for Si and SiGe (5% Ge). As diffusion is found to be faster in SiGe than in Si. As diffusion coef. (cms -2 )

Diffusion in Isotopically Controlled Silicon-Germanium Alloys Eugene E. Haller, University of California, Berkeley, DMR Education: A graduate student, Chris Liao, performs Ge and SiGe diffusion research. This past summer, he has spent two months working in the group of Professor H. Bracht, one of our international collaborators at the University of Münster in Germany. Broader impact: The ever-increasing demands for improving the performance of modern microelectronic devices has lead to diminishing device dimensions and deployment of advanced materials such as SiGe and Ge. Thus, precise control of the motion of dopants in these advanced materials becomes essential for high performance devices. However, fundamental scientific knowledge of atomic-scale diffusion mechanisms in these materials is mostly unknown. Therefore, determination of these diffusion properties through the research presented here will enable optimal processing of new generation of devices down to the nanometer scale. Since such data are essential to industrial manufacturers and scientists alike, our research group is an active member of a university- semiconductor industry collaboration. Above: Schematic of the isotopically engineered Si 1-x Ge x heterostructure used for simultaneous determination of self- and dopant diffusion. The effect of strain can also be studied by varying x and y. These experiments provide a means to determine complete, atomic-level diffusion mechanisms and defect energy levels in this advanced materials system. Si substrate SiGe graded buffer layer 100 nm nat. Si 1-y Ge y 200 nm 28 Si 1-x 70 Ge x