On the page 117407-3, left column, the text in the last paragraph should be written as follows. ''Such a small L m value means that the respective clusters are elongated along the electric field vector of the incident light, like the interface indium inclusions. In this case, the depolarization is small, and the resonance energy is the lowest among those possible [16]. This type of clusters determines the effective absorption edge in InN. The resonances of the clusters with L m 0:33 are higher in energy than the absorption edge in InN, so the prolate intercolumn inclusions do not affect the effective band edge.'' This correction affects the speculation concerning the type of the In clusters involved, but changes none of our main results.We thank T.

The refractive indices of several AlxGa1−xN alloys deposited on silicon are determined by ellipsometry and reflectivity experiments at room temperature. The AlGaN layers are grown on (111)Si substrate by molecular-beam epitaxy on top of an AlN/GaN/AlN buffer in order to reduce the strain of the alloy. The Al composition is deduced from energy dispersive x-ray spectroscopy and photoluminescence experiments. The refractive index n and the extinction coefficient k are determined in the 300–600 nm range. For the transparent region of AlxGa1−xN, the refractive index is given in form of a Sellmeier law.

Mie resonances due to scattering or absorption of light in InN-containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than the currently accepted 0.7 eV. Microcathodoluminescence studies complemented by the imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises in a close vicinity of In inclusions and is likely associated with surface states at the metal/InN interfaces.

In order to clarify the nature of the neutral Mn acceptor in GaP, we have carried out optical-absorption and electron-paramagnetic-resonance ͑EPR͒ experiments using both conventional and thermally detected EPR on semi-insulating GaP:Mn. In thermal equilibrium at low temperatures, all the manganese occurs in the charged acceptor state Mn Ga 2ϩ ͑A Ϫ ͒. By illumination with photon energies greater than 1.2 eV, it can be partially converted into the neutral charge state. The arising photostimulated EPR spectrum shows the characteristic of a tetragonally distorted center with an integer spin. The resonance lines are detectable only at temperatures below 7 K, and their linewidth of about 50 mT is due to the unresolved Mn-hyperfine splitting. We interpret the experimental data in terms of Mn Ga 3ϩ ions on strain-stabilized sites of tetragonal symmetry due to a strong T ⑀ Jahn-Teller coupling within the 5 T 2 ground state. Such a behavior is expected for a 3d 4 defect, as observed for the isoelectronic impurity Cr 2ϩ in GaAs, and other tetrahedrally coordinated semiconductors. The analysis of the EPR spectra thus verifies that, in GaP, the neutral charge state of the Mn acceptor is Mn Ga 3ϩ ͑A 0 ͒ in contrast to its behavior in GaAs and InP. ͓S0163-1829͑96͒06139-5͔