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We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and AlxGa1-xN (x<0.3) layers were grown by molecular beam epitaxy on GaAs and Si(111) substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The properties of Co–Si thin films grown by the thermal sintering of Co and Si layers are studied. Co and Si layers are produced by chemical vapor deposition. To form cobalt silicide, the obtained two-layer structure is annealed at a temperature of 760 K for 12 h. The thermoelectric properties of the film structure are studied in the temperature range of 300–800 K. The temperature dependences of the thermoelectric power and resistivity, as well as structural data, indicate the formation of a multilayer structure containing layers with excess silicon and cobalt. [ABSTRACT FROM AUTHOR]

In this letter, we study the optical properties of GaN1-xSbx thin films. Films with an Sb fraction up to 42% were synthesized by alternating GaN-GaSb layers at a constant temperature of 325 °C. The measured optical absorption data of the films are interpreted using a modified band anticrossing model that is applicable to highly mismatched alloys such as GaN1-xSbx in the entire composition range. The presented model allows us to more accurately determine the band gap as well as the band edges over the entire composition range thereby providing means for determining the composition for, e.g., efficient spontaneous photoelectrochemical cell applications. [ABSTRACT FROM AUTHOR]

Summary Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light-emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality. In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1° towards [1010]GaN ), where the tilt is due to the inclination of the sapphire substrate (cut off-axis by 10° from (0001)sapphire towards (1010)sapphire ). We compare EBSD patterns obtained from As-doped GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) with low and high As4 flux, respectively. Higher As4 flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled. [ABSTRACT FROM AUTHOR]

Amorphous GaN1-xAsx layers with As content in the range of x=0.1 to 0.6 were grown by molecular beam epitaxy on Pyrex glass substrate. These alloys exhibit a wide range of band gap values from 2.2 to 1.3 eV. We found that the density of the amorphous films is ∼0.8–0.85 of their corresponding crystalline value. These amorphous films have smooth morphology, homogeneous composition, and sharp well defined optical absorption edges. The measured band gap values for the crystalline and amorphous GaN1-xAsx alloys are in excellent agreement with the predictions of the band anticrossing model. The high absorption coefficient of ∼105 cm-1 for the amorphous GaN1-xAsx films suggests that relatively thin films (on the order of 1 μm) are necessary for photovoltaic application. [ABSTRACT FROM AUTHOR]

The electrical properties of p-type cubic (Ga,Mn)N films are reported. Hole concentrations above 1018 cm-3 at room temperature are observed. Activated behavior is observed down to 150 K, with an acceptor ionization energy of around 45–60 meV. The dependence of hole concentration and ionization energy on Mn concentration indicates that the shallow acceptor level is not simply due to unintentional codoping. Thermopower measurements on freestanding films, capacitance–voltage profilometry, and the dependence of conductivity on thickness and growth temperature, all show that this is not due to diffusion into the substrate. We therefore associate the p-type conductivity with the presence of the Mn in the cubic GaN films. [ABSTRACT FROM AUTHOR]