T.L. Tansley

Optical band gap of indium nitride

Room‐temperature optical absorption data in the 1.5–2.5‐eV range are reported for indium nitride thin films prepared by reactive radio‐frequency sputtering. The fundamental absorption edge in high‐purity material is located at 1.89±0.01 eV and corresponds to a direct transition at k=0, in agreement with band‐structure calculations. A significant Moss‐Burstein shift is noted for carrier concentrations in excess of 1019 cm−3 and obeys the empirical relationship EG =1.89+2.1×10−8 n1/3 eV.

Electron mobilities in gallium, indium, and aluminum nitrides

Electron mobilities in GaN and InN are calculated, by variational principle, as a function of temperature for carrier concentrations of 1016, 1017, and 1018 cm−3 with compensation ratio as a parameter. Both GaN and InN have maximum mobilities between 100 and 200 K, depending on the electron density and compensation ratio, with lower electron density peaking at lower temperature. This is due to the interplay of piezoelectric acoustic phonon scattering at low carrier concentrations and ionized impurity scattering at higher carrier concentrations. Above 200 K, polar mode optical phonon scattering is the mobility limiting process. The 300 and 77 K electron and Hall mobilities as functions of carrier concentration in the range of 1016–1020 cm−3 and compensation ratio are also calculated. The theoretical maximum mobilities in GaN and InN at 300 K are about 1000 and 4400 cm2 V−1 s−1, respectively, while at 77 K the limits are beyond 6000 and 30 000 cm2 V−1 s−1, respectively. We compare the results with experimen...

Variable range hopping in polypyrrole films of a range of conductivities and preparation methods

The electronic transport mechanism in polypyrrole is discussed in terms of Mott variable range hopping (VRH) in samples with a wide range of conductivities and which have been formed using different doping techniques. Samples were synthesized in both aqueous and organic media and samples were either doped during polymerization or dedoped afterwards giving a three order of magnitude range of conductivities at 300 K and a range of sample morphologies. No difference in behavior is observed for materials with different morphologies, suggesting that transport predominantly involves monomer units and occurs independent of structure. The various transport parameters obtained appear reasonable with the exception of the apparent ‘‘hopping attempt frequency,’’ related to the phonon frequency in VRH, some values of which are anomalously high. The density of states at the Fermi level was found to be between 5×1018 and 1×1022 eV−1 cm−3 for a range of samples and the mean hopping distances ranged between 2 and 34 monom...

Nitrogen-rich indium nitride

K.S.A.B. would like to acknowledge the support of an Australian Research Council Fellowship. We would also like to acknowledge the support of the Australian Research Council through a Large grant and a Discovery grant; the support of a Macquarie University Research Development Grant, and the Australian Institute of Nuclear Science and Engineering for SIMS access.

Laser‐induced chemical vapor deposition of AlN films

AlN intended for metal‐insulator‐semiconductor applications has been prepared by laser activated chemical vapor deposition from ammonia and trimethylaluminum precursors. The films are high‐density polycrystalline with 〈100〉 preferential orientation, and there is no evidence of the presence of Al2O3. A consistent band gap of 6.00±0.03 eV is obtained for film thickness in the range 0.3–1.2 μm. Conductivity is below 5×10−14 Ω−1 cm−1 at room temperature and is thermally activated with a range of excitation energies between 0.6 and 0.8 eV. The breakdown electric field is about 3×106 V/cm, while the relative permittivity varies between 7.8 and 8.2 in the frequency range 100 Hz–13 MHz.

Structural studies of reactively sputtered carbon nitride thin films

The structure of reactively sputtered carbon nitride thin films has been investigated using infrared, Raman and X-ray photoelectron spectroscopies. The presence of infrared and Raman active C-N vibrational bands and the chemical shifts of the C ls and N ls photoelectron levels observed in our films reveal that the nitrogen atoms incorporated in the films are chemically bonded to the carbon atoms.

Elemental composition and microstructure of reactively sputtered carbon nitride thin films

Thin films of carbon nitride have been grown on various substrates using low power radio frequency reactive sputtering of graphite in pure nitrogen plasma. A quantitative composition analysis using Rutherford backscattering spectrometry shows that the film contains about 51 at. % C, 44 at. % N, and 5 at. % O. The study of the microstructure of the films using cross‐sectional scanning electron microscopy reveals highly oriented columnar structures.

X‐ray photoelectron spectroscopy characterization of radio frequency reactively sputtered carbon nitride thin films

Carbon nitride thin films prepared by radio frequency reactive sputtering of graphite in pure nitrogen plasma have been characterized by x‐ray photoelectron spectroscopy (XPS) for probing the chemical bonding in the films. The multiple binding energy values obtained for the C 1s and N 1s photoelectrons in the film suggest that both the C and N atoms exhibit at least three types of chemical states, manifestative of different types of the C–N bonding present in the material. The presence of theoretically predicted β‐C3N4 phase in our C–N films has been suggested on the basis of XPS and optical data.

Conductivity degradation in oxygen‐aged polypyrrole

The conductivity of doped polypyrrole, as high as 100 Scm−1 in freshly prepared samples, falls slowly with time on exposure to atmospheric oxygen. Typically, the fall in conductivity is fairly slow at room temperature, but the process can be accelerated by heating samples and measuring the decrease in conductivity as a function of time. Analysis of the kinetics of this process shows a preliminary, 120 min regime in which a surface adsorption‐diffusion mechanism with an activation energy of 0.41 eV appears to mediate. Once a degree of adsorbate saturation is attained subsequent behavior is well described by standard bulk diffusion considerations and is activated at 0.48 eV. We propose a mechanism whereby oxygen adsorption onto the surfaces of the polymer fibrils and diffusion into the interior are respective rate limiting steps in the incorporation of oxygen into the closely cross‐linked mesh, blocking conducting pathways.

Infrared absorption in indium nitride

The room‐temperature optical absorption spectra of indium nitride films in the subband‐gap energy range 40 meV to 2.0 eV are surveyed. The major features are two broad absorption bands: a band‐edge tail with a threshold energy of about 1 eV and a broad peak centered at about 0.3 eV. Both are strongly sample dependent and are identified with crystal defects associated with the observed electrical compensation of the shallow donor impurity. All samples show optical excitation of the 50–60‐meV shallow donor seen in thermal excitation measurements, while some exhibit an absorption doublet, whose nature is not understood, around 0.15 eV.