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HL: Halbleiterphysik

HL 9: Poster I

HL 9.12: Poster

Montag, 27. März 2006, 15:15–17:45, P3

Why does the level-repulsion model fail in the vicinity of the GaN_xP_1−x indirect gap? — •M. Güngerich¹, P.J. Klar¹, W. Heimbrodt¹, G. Weiser¹, J.F. Geisz², C. Harris³, A. Lindsay³, and E.P. O Reilly³ — ¹Dept. of Physics and Material Sciences Center, Philipps-University, Renthof 5, D-35032 Marburg, Germany — ²National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA — ³Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland

The character of the fundamental band gap of P-rich GaN_xP_1−x has been under controversial discussion during the last few years. By electromodulated absorption studies of MOVPE-grown GaN_xP_1−x with 0.0 ≤ x ≤ 0.029, we prove that a simple parametrization of the electronic structure in the energy range of the N localized levels according to a two-level repulsion-model fails in this material. The Γ character of electronic transitions in the range of the N levels is shown to be spread over several sharp transitions rather than concentrated in a single E₋ transition. Pressure-dependent photoluminescence indicates a purely impurity-like character of these transitions. For ordered structures containing well separated N atoms the applicability of the level-repulsion model is confirmed by tight-binding calculations. As soon as, due to statistical spatial N-distribution, N pairs and clusters are formed the model breaks down and needs to be replaced by the Linear Combination of Isolated Nitrogen States (LCINS) approach. Photocurrent measurements confirm the widely observed blue shift of the GaP-like E₊ band gap.