D. Behr et al., EVIDENCE FOR COMPOSITIONAL INHOMOGENEITY IN LOW IN CONTENT (INGA)N OBTAINED BY RESONANT RAMAN-SCATTERING, Applied physics letters, 73(2), 1998, pp. 241-243
Resonant Raman scattering has been used to study hexagonal InxGa1-xN f
ilms with x approximate to 0.1, grown by metal-organic chemical vapor
deposition on sapphire substrates. To vary the energy difference betwe
en the fundamental gap energy of the (InGa)N and the photon energy of
the discrete laser emission lines used for recording the spectra, the
sample temperature was varied between 300 and 870 K. Raman scattering
by the (InGa)N A (1)(LO) phonon shows a clear resonance profile when t
he fundamental energy gap approaches the incident photon energy, with
a maximum enhancement in scattering efficiency of 10 measured relative
to the scattering strength of the E-2 phonon mode. The (InGa)N A (1)(
LO) phonon was found to shift to higher frequencies with respect to th
e E-2 mode when the experimental conditions were varied from excitatio
n below the fundamental energy gap of (InGa)N to above-band-gap excita
tion. This frequency shift is explained by the presence of composition
al inhomogeneity, which results in localized regions with higher In co
ntent, and thus, lower gap energy and phonon frequency, and regions wi
th lower In content, and consequently, higher gap energy and phonon fr
equency. (C) 1998 American Institute of Physics. [S0003-6951(98)03328-
2].