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We report a firm evidence of luminescence from InN clusters in InGaN/GaN multiple quantum wells. Photoluminescence, photoluminescence excitation, and Raman scattering measurements have been employed to study the optical properties of InGaN/GaN multiple quantum wells. A careful examination of the low energy shoulders of the main peak luminescence reveals the fact that their separation is in good agreement with the longitudinal optical phonon energy of pure InN film measured by Raman scattering. A large Stokes-like shift between the emission peak energy and the absorption edge is found; it increases with increasing indium content. All these observations can be explained in a consistent way by the effect of localization due to self-organized InN clusters within InGaN layers. Our results thus strongly suggest that the emission mechanism of InGaN/GaN quantum wells originates from radiation recombination within the localized states of self-organized InN clusters. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the preparation and field emission properties of quasi-aligned silicon carbon nitride (SiCN) nanorods. The SiCN nanorods are formed by using a two-stage growth method wherein the first stage involves formation of a buffer layer containing high density of nanocrystals by electron cyclotron resonance plasma enhanced chemical vapor deposition and the second stage involves using microwave plasma enhanced chemical vapor deposition for high growth rate along a preferred orientation. It should be noted that growth of the SiCN nanorods is self-mediated without the addition of any metal catalyst. Scanning electron microscopy shows that the SiCN nanorods are six-side-rod-shaped single crystals of about 1-1.5 μm in length and about 20-50 nm in diameter. Energy dispersive x-ray spectrometry shows that the nanorod contains about 26 at. % of Si, 50 at. % of C, and 24 at. % of N. Characteristic current-voltage measurements indicate a low turn-on field of 10 V/μm. Field emission current density in excess of 4.5 mA/cm[sup 2] has been observed at 36.7 V/μm. Moreover, SiCN nanorods exhibited rather stable emission current under constant applied voltage. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Detailed piezoreflectance (PzR) measurements of quasialigned silicon carbon nitride nanorods in the temperature range between 15 and 400 K were performed. The direct band-to-band transition energies E[sub g][sup d] at various temperatures were determined accurately through line shape fit of the experimental PzR spectra. The temperature dependence of E[sub g][sup d] is analyzed by the Varshni equation [Y. P. Varshni, Physica, (Amsterdam) 34, 149 (1967)] and an expression containing the Bose-Einstein occupation factor for phonons proposed by L. Vin˜a, S. Logothetidis, and M. Cardona [Phys. Rev. B 30, 1979 (1984)]. The parameters that describe the temperature dependence of E[sub g][sup d] are evaluated and discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]