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HL: Halbleiterphysik

HL 42: Elektronentheorie

HL 42.7: Talk

Friday, March 31, 2000, 12:00–12:15, H14

Polar GaN surfaces: comparison between LDA and GGA — •Andreia Rosa, Martin Fuchs, and Jörg Neugebauer — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

Polar GaN surfaces are relevant for epitaxial growth of GaN and have been experimentally^[1] and theoretically well studied. Theoretically, most of the studies employed density-functional theory within LDA.^[2] In order to improve the calculations in a systematic way we have studied the effect of the exchange-correlation functional on the electronic structure, atomic geometry and energetics of GaN surfaces. Specifically we have considered several reconstructed GaN(0001) surfaces. We find that the PBE-GGA leads to a somewhat enlarged lattice constant. The relative atomic coordinates of the reconstructed surfaces remain however virtually unchanged. Further, PBE-GGA gives a smaller fundamental band gap compared to the LDA calculation. Our analysis showed that this is solely due to the larger lattice constant; at the same lattice constant LDA and PBE-GGA give exactly the same band gap and surface bands. Finally, a different qualitative behaviour for the surface energies is found. While the N (2×2) adatom structure is found to be the most stable for N-rich conditions employing LDA, this behaviour is not observed for the PBE-GGA. The origin is that PBE-GGA severely underestimates the thermodynamically allowed range of chemical potentials.

[1] A. R. Smith et al, Surface Science 423, 70 (1999).

[2] T. Zywietz, J. Neugebauer, and M. Scheffler, Appl. Phys. Lett. 73, 487 (1998).