Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 7: Semiconductor substrates
O 7.1: Vortrag
Montag, 23. März 2009, 11:15–11:30, SCH A315
Electronic structure of the cleaved non-polar GaN(1100) surface — •P. Löptien1, M. Bertelli1, M. Wenderoth1, R.G. Ulbrich1, A. Rizzi1, J. Malindretos1, M.C. Righi2, A. Catellani3, A. Ferretti2, and L.C. Samos2 — 1IV. Phys. Inst., Univ. Göttingen, Germany — 2Dip. Fisica, Modena, Italy — 3CNR, Parma, Italy
The non-polar GaN(1100) surface (m-plane) has recently gained importance due to the demonstration of high-efficiency LEDs and LDs. A thorough microscopic understanding of this surface is therefore of great interest. Up to now the existence of surface states within the bandgap at the Γ point of the Brillouin zone is an open question. We performed cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS) and ab initio DFT-LDA simulations of this surface. Our calculations suggest an unreconstructed surface and no surface state bands inside the gap at Γ. The Ga derived empty surface state band is found to be degenerate with the CB minimum. In experiment, the unintentionally n-doped GaN(0001) samples grown by HVPE were thinned to ∼100 µm. They were cleaved in UHV along the m-plane and measured in-situ at room temperature. The experiments confirmed clearly the unreconstructed surface. The current measured by STS at different voltages can be explained with tip-induced band bending (TIBB). Conduction band states are addressed both at positive and negative bias voltages. This is confirmed by a simulation with a one-dimensional Poisson equation solver. We conclude that the Fermi-level is not pinned on clean cleaved surfaces. It follows that the bandgap has no intrinsic surface states at the Γ point of the BZ.