| AVS 61st International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuP |
| Session: | Electronic Materials and Processing Poster Session |
| Presenter: | Sang Choi, NASA Langley Research Center |
| Authors: | S.C. Choi, NASA Langley Research Center H.J.K. Kim, National Institute of Aerospace |
| Correspondent: | Click to Email |
Silicon-geranium (SiGe) is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors.[1] Semiconductor chipsets and devices require a single-crystalline phase of material without defects, while thermoelectric materials need granulated domains of poly crystalline structure with an interfacing boundary electrically connected but causing phonon scattering.[2] The structural formation between SiGe and substrate can be tailored for either single crystal or twin lattice structure.
Highly ordered single crystals with rhombohedral epitaxy using an atomic alignment of the [111] direction in cubic SiGe with the [0001] direction in the sapphire basal plane (c-plane) have been successfully grown at the NASA Langley Research Center. The changes in the growth temperature (from 820oC to 890oC) strongly influence the shape, size and density of the SiGe nuclei in the early growth stage and eventually the film morphology and defect density in the final growth stage. Annular bright field (ABF) and high angular dark field (HAADF) scanning transmission electron microscopy (STEM) were used to investigate the atomic structure and chemistry of SiGe and sapphire (Al2O3) interfaces, sapphire substrate reconstruction, and defects for studying the film growth mechanism. The best growth condition can be achieved by choosing the suitable substrate temperature and kinetic energy of impinging Si and Ge atomic flux. By controlling the kinetic energy of the surface atoms, either a dominant twin crystal or dominant single crystal was steadily formed. The kinetic energy of surface atoms is determined at the growth temperature between 820oC and 890oC.
[1] D. L. Harame and B. S. Meyerson, IEEE Transactions on Electron Device, 48 (11), 2555 (2001).
[2] C. Gui, M. Elwenspoek, N. Tas, and J. G. E. Gardeniers, J. Appl. Phys. 85 (10), 7448 (1999).