Regensburg 2004 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 43: III-V Halbleiter II

HL 43.1: Vortrag

Donnerstag, 11. März 2004, 15:15–15:30, H14

Raman spectroscopy of Ga(As,N) epitaxial layers under hydrostatic pressure — •M. Güngerich¹, P.J. Klar¹, W. Heimbrodt¹, J. Koch¹, W. Stolz¹, M.P. Halsall², and P. Harmer² — ¹FB Physik und WZMW, Philipps-Universität, Marburg, Germany — ²Dept. Physics, UMIST, Manchester, United Kingdom

Vibrational modes of GaAs_1−xN_x layers were studied by Raman spectroscopy at hydrostatic pressures up to 20 GPa. Lattice vibrations of Ga(As,N) show a two-mode behaviour typical of a system where the impurity atoms are considerably lighter than the host atoms. The N atoms vibrate independently of the GaAs-like phonons and give rise to a local vibrational mode (LVM) visible in the spectra for x>0.005. Pure GaAs is known to undergo a phase transition from the zincblende structure to an orthorhombic structure in the pressure range between 15 and 20 GPa. In the investigated GaAs_0.915N_0.085 sample the phase transition indicated by the disappearance of the GaAs-like phonons takes place at about 19 GPa. Up to that pressure, the pressure coefficients of the optical phonons are similar to those of GaAs. The LVM shifts to higher frequencies at a significantly higher rate. This behaviour can be understood assuming that the pressure induced changes of the bond lengths are the same as in pure GaAs. It can be shown that the anharmonicity of the Ga-N bonds in Ga(As,N) is smaller than in GaN.