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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology



Friday, 22 November 2002
(at 11:00 in room MPIPKS-SR3)
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Understanding adsorption of Si at GaN (0001) surfaces using first-principles calculations

Andreia Luisa da Rosa

Theorie
Fritz-Haber-Institut der Max-Planck Gesellschaft
Berlin    






Silicon is the most common impurity used as n-type dopant in GaN. While the properties of Si in bulk GaN are well established little is known regarding its effect on surfaces or its incorporation mechanism. Recent growth experiments indicate that Si significantly affects the growth morphology and may even act as an anti-surfactant. We have therefore performed a systematic study of Si adsorption at (0001) GaN surfaces combining first-principles calculations and scanning tunneling microscopy (STM). Calculating the surface energy of a large number of structures with various Si concentrations and various III-V ratios we derive a phase diagram showing the energetically most stable surfaces as a function of the Si and N chemical potentials. Based on these results we identify the equilibrium surfaces and explain the structures seen in the STM study. The most favorable structures consist of Si residing at subsurface sites, demonstrating efficient incorporation of Si. It is in contrast to all other previously studied impurities, like for example O, In, and Mg, where the most stable configurations consist of impurities on the surface, instead of incorporation in the bulk region. Under Ga-rich/Si-rich conditions Si is buried at subsurface sites, while under N-rich/Si-rich conditions, we found that adsorption of Si leads to the inversion polarity of the GaN (0001) surfaces. Consequences for Si-doping and growth morphology will be discussed.

Invited by G. Cuniberti (MC seminar)

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