Hamburg 2001 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 23: GaN I
HL 23.4: Vortrag
Dienstag, 27. März 2001, 16:15–16:30, S2
Adsorption and incorporation of Si at (0001)GaN surfaces: the interplay between bulk solubility and Si3N4 formation — •A.L. Rosa1, J. Neugebauer1, J.E. Northrup2, C.D. Lee3, and R.M. Feenstra3 — 1Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany — 2Xerox PARC, 3333 Coyote Hill Road, Palo Alto, 94304, USA — 3Department of Physics, Carnegie Mellon University, Pittsburgh, PA 5213, USA
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. Analyzing all the structures we identify two competing processes so far not observed for other impurities in GaN. On one side the most favorable structures consist of Si residing in subsurface sites, demonstrating efficient incorporation of Si. On the other hand, all Si-induced surface reconstructions are unstable against Si3N4 formation, i.e., formation of Si3N4 is a likely cause for the anti-surfactant behavior of Si on GaN.