Optical investigations of AlGaN on GaN epitaxial films

Abstract

We investigated coherently strained AlxGa1−xN/GaN heterostructures (0<x<0.22) grown by metalorganic vapor phase epitaxy on sapphire with photoluminescence (PL), reflexion and cathodoluminescence experiments. The energetic positions of the free A exciton as a function of the alloy compositions are deduced from temperature dependent PL and from reflexion measurements. We obtain a small bowing parameter and no evidence for a Stokes shift between absorption and emission. Compositional inhomogeneities are present, but the fluctuations are too small to be important for carrier localization. The broadening of the luminescence linewidth in the alloys can be described by statistical disorder of a random alloy.

Growth of AlxGa1−xN-layers on planar and patterned substrates

“…The PL FWHM was evaluated and fit by a model described in Ref. [8] based on alloy broadening. The FWHM data were fit quite well indicating that the optical quality is good and that alloy broadening is dominant in the Al x Ga 1Àx N-layers.…”

Aluminum incorporation in -layers and implications for growth optimization

“…We can compare the FWHM for these samples in PL since the PL line spectral positions are very close. That would not be possible if they would differ strongly: it is well known that for increasing Al concentration the alloy fluctuations [15] increase. On the other hand, we conclude that the usage of nitrogen or hydrogen will not dramatically change the Al composition.…”

Structural and optical properties of Zn(Mg,Cd)O alloy films grown by remote-plasma-enhanced MOCVD

“…The exciton in oxide semiconductor seems to be easily localized by the alloy fluctuation, because ZnO-based semiconductor has strong electronegativities and the small Bohr radius of exciton. The PL FHWM of various ternary alloy II-VI and III-V semiconductors on alloy content has been analyzed by theoretical model based on the statistical alloy fluctuation [28][29][30][31]. The localization of the exciton in oxide semiconductors seems to occur at the minima of the potential fluctuation caused by alloy fluctuation, showing larger PL FWHM compared with typical AlGaN-based system [31] and, however, there has been very few reports on just Mg y Zn 1 À y O system [32] yet.…”