Structure Of Aluminum Nitride Research Articles

Room-temperature magnetism in Cr-doped AlN semiconductor films

Synthesis and characterization of magnetic semiconductors Al1−xCrxN, in which the atomic fraction of chromium x is up to 0.357, are reported. The films, grown by reactive co-sputtering on silicon, glass, and kapton substrates, have a crystal structure of aluminum nitride. Magnetic and transport properties were studied in the temperature range of 50 to 340 K. The materials are in the dielectric regime and have variable-range-hopping type of conductance. The films are ferromagnetic at temperatures over 340 K.

Distinct orientation of AlN thin films deposited on sapphire substrates by laser ablation

Crystalline, 50- 1200 nm thick aluminum nitride (AlN) films were deposited on sapphire by laser ablation of sintered AlN targets. On c-, r-, m-, and a-cut sapphire the AlN films were .00:1/, .11:0/, .10:0/ ,a nd.00:1/ oriented, respectively. X-ray diffraction goniometry revealed the in- plane orientation of AlN on c-, r-, and m-cut sapphire to be c: AlNT1000UjjAl2O3T2100U, r:AlNT2010UjjAl2O3T1000U ,a nd m: AlNT0100UjjAl2O3T0001U. TEM showed a smooth surface of AlN.11:0/ grown on r-cut sapphire in contrast to a rough surface and columnar structure of AlN.00:1/ films on c-cut sapphire. AFM revealed atomically flat films at initial stages of film growth independent of the substrate orientation. Thick AlN films on c-cut sapphire were rough whereas those on r-cut sapphire remained smooth up to 1 mm thickness with a rms-roughness as low as 1n m.

Electronic states at aluminum nitride (0001)-1×1 surfaces

We investigate the electronic structure of aluminum nitride (0001)-1×1 surfaces via direct and inverse photoemission spectroscopy. Bulk and surface sensitive measurements on clean surfaces and surfaces exposed to oxygen or cesium demonstrate the existence of filled and empty surface states which extend more than 1 eV beyond the valence- and conduction-band edges. The filled states are tentatively associated with Al dangling or back bonds. The measurement of the top of the valence band upon removal of the filled states leads to a determination of an electron affinity equal to 1.9±0.2 eV. The empty surface states are presumed to play a role in the pinning of the Fermi level in the upper part of the gap and are consistent with the anticipated metallicity of the surface.

Quantitative analysis of valence electron energy-loss spectra of aluminium nitride.

The optical properties and electronic structure of aluminium nitride are determined using valence electron energy-loss spectroscopy in a dedicated scanning transmission electron microscope. Quantitative analysis of the experimental valence electron energy-loss spectra to determine the electronic structure encompasses single scattering deconvolution of the valence electron energy-loss spectra to calculate the energy-loss function, Kramers-Kronig analysis of the energy-loss function to reveal the complex dielectric function, transformation of the dielectric function into the optical interband transition strength via optical property relations and finally critical-point analysis of the interband transition strength. The influence of both experimental and analytical parameters on the final result was studied systematically to define and improve the understanding of the methods. To check the reliability of this technique the interband transition strength determined was compared with results of vacuum ultraviolet spectroscopy. Good agreement was found if sample preparation was taken into account. The preparation of the specimen for the transmission electron microscopy has an effect on the electronic structure. Quantitative analysis of valence electron energy-loss spectroscopy, using the methods presented, is an important and capable method to determine the electronic structure of materials and it has the benefit of high spatial resolution.

The microstructure and properties of a buried AIN layer produced by nitrogen implantation into pure aluminum

A buried aluminum nitride (AIN) layer was formed by nitrogen ion implantation into pure aluminum with doses of 10, 18 and 28 × 10 17 N + cm −2 at 200 keV. In order to analyze the profile of the implanted nitrogen in aluminum, 3.5 MeV 4He + backscattering was used, in preference to 2.0 Mev 4He + backscattering. A rectangular-like profile of the implanted nitrogen was obtained from the Rutherford backscattering spectra after the dose of 10 × 10 17 N + cm −2. The nitrogen to aluminum ratio at the rectangular-like profile is about 0.9–1.0. The results of X-ray diffraction and transmission electron diffraction indicated that aluminum nitride structure is essentially the hexagonal crystal. Aluminum nitride with f.c.c. structure also appeared on nitrogen implantantion into aluminum. This is a transient structure. The resistivity of AIN formed by nitrogen implantation into aluminum is about (1.4−2.0) × 10 12 Ω cm.

Transmission Electron Microscopy Studies of (AIN-Si3N4) Codeposits Obtained by LPCVD

Several (Al,Si,N) compounds have been obtained by LPCVD in a vertical hot-wall reactor using aluminium trichloride, silicon tetrachloride and ammonia as source gases, with nitrogen as the carrier gas. In order to determine both their structure and local chemical composition, several deposits have been examined by analytical transmission electron microscopy combining electron diffraction (ED), high resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS). It has been confirmed that the chemical composition of the materials as well as the size of the nanocrystals observed in the deposits are strongly dependent on the temperature and the reactive gas flow. It has also been shown that for the range of temperature (1273 K-1373 K) used in this work these nanocrystals have the wurtzite structure of aluminium nitride.

Oxygen incorporation in aluminum nitride via extended defects: Part I. Refinement of the structural model for the planar inversion domain boundary

The model proposed by Harris et al. [J. Mater. Res. 5, 1763–1773 (1990)], describing planar inversion domain boundaries in aluminum nitride, consists of a basal plane of aluminum atoms octahedrally coordinated with respect to oxygen, and with a translation of R = 1/3〈1011〉. This thin sandwich is inserted onto the basal plane of the wurtzite structure of aluminum nitride. This model does not take into consideration any interfacial relaxation phenomena, and is arguably electrically unstable. Therefore, this paper presents a refinement of the model of Harris et al., by incorporating the structural relaxations arising from modifications in local chemistry. The interfacial structure was investigated through the use of conventional transmission electron microscopy, convergent electron diffraction, high resolution transmission electron microscopy, analytical electron microscopy, and atomistic computer simulations. The refined planar inversion domain boundary model is closely based on the original model of Harris et al.; however, the local chemistry is changed, with every fourth oxygen being replaced by a nitrogen. Atomistic computer simulation of these defects, using a classical Born model of ionic solids, verified the stability of these defects as arising from the adjustment in the local chemistry. The resulting structural relaxations take the form of a 0.3 mrad twist parallel to the interface, a contraction of the basal planes adjacent to the planar inversion domain boundary, and an expansion of the c-axis component of the displacement vector; the new displacement vector across the interface is R = 1.3〈1010〉 + ∊〈0001〉, where ∊meas = 0.387 and ∊calc = 0.394.

Morphology and orientation of nanocrystalline AlN thin films

This paper describes the surface morphology, composition, and structure of aluminum nitride (AlN) thin films formed by single ion-beam sputtering of Al. Either pure N 2 or a N 2 (75%) + H 2 (25%) gas mixture was used as the feed gas for the ion gun. The films formed from the hydrogen containing feed gas were deposited on substrates either at room temperature or at 200°C. The film surface was extremely smooth for films grown under all the deposition conditions: scanning force microscopy indicated ⩽ 1 nm average roughness over a 500 × 500 nm 2 area. Transmission electron microscopy examination of the films showed that they were highly textured: the c axis of the AlN grains is preferentially oriented perpendicular to the film/substrate interface. The films grown with pure N 2 consisted of grains in the order of 100 nm in diameter whereas films formed with a hydrogen containing feed gas had at least an order of magnitude smaller grain size.

Structure of aluminium nitride with additions of titanium nitride oxide and carbide: S.A. Satanin et al Poroshkovaya Metallurgiya, No 9, 1992, 69–74 (In Russian)

Structure of aluminium nitride with additions of titanium nitride oxide and carbide: S.A. Satanin et al Poroshkovaya Metallurgiya, No 9, 1992, 69–74 (In Russian)

Electronic structure of aluminum nitride: Theory and experiment

We report the results of a vacuum ultraviolet (VUV) study of single crystal and polycrystalline AlN over the range 4–40 eV and compare these with theoretical optical properties calculated from first principles using an orthogonalized linear combination of atomic orbitals in the local density approximation. The electronic structure of AlN has a two-dimensional (2D) character indicated by logarithmic divergences at 8.7 and 14 eV. These mark the centers of two sets of 2D critical points which are associated with N 2p→Al 3s transitions and Al=N→Al 3p transitions, respectively. A third feature is centered at 33 eV and associated with N 2s→Al 3d transitions.

Electronic structure of high pressure phase of AlN

Results of ab initio Hartree–Fock calculations for the electronic structure of aluminum nitride in the (high-pressure) rocksalt phase are reported. In the rocksalt phase, the calculated lattice constant is 3.982 Å with the bulk modulus of 329 GPa. The band structure is predicted to be indirect at the X point with a gap of 8.9 eV. In this phase, the bonding is shown to be essentially ionic between Al and N. The direct gap shows a stronger linear dependence on pressure with a pressure derivative of 68 meV/GPa compared to that of the indirect gap with a pressure derivative of 31.7 meV/GPa.

Deposition of AlN films onto Fe-Al-Mn alloys by reactive r.f. magnetron sputtering

Aluminum nitride (AlN) thin films were deposited onto austenitic Fe-Al-Mn alloys by reactive r.f. magnetron sputtering with a mixture of argon and nitrogen. Various N 2 contents and deposition times were employed to carry out the deposition. The deposition rate decreases as the N 2 content is increased and the deposition thickness increases linearly with deposition time for a fixed N 2 content. The structure, morphology and elemental distribution were analyzed using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and electron probe microanalysis. The growth habits of AlN films are strongly dependent on the deposition rate. Transmission electron diffraction patterns reveal that a polycrystalline h.c.p. AlN structure is present.