Properties Of AlN Thin Films Research Articles

Effects of argon/nitrogen sputtering gas on the microstructural, crystallographic and piezoelectric properties of AlN thin films

The growth of highly crystalline c-plane AlN ‹002› is extremely difficult, entailing high temperature and ultra-high vacuum condition. In sputtering technique, the addition of nitrogen into argon sputtering gas can significantly assist the formation of AlN ‹002› at low temperature. We incorporated purified nitrogen gas and observed the consistent formation of single crystal ‹002› AlN thin film layer sputter-deposited on Mo/Si substrate from the AlN ceramic target. Small presence of oxygen content within AlN crystal relates to the preferential growth of AlN ‹002›. High oxygen content in AlN thin film due to the use of unpurified nitrogen and argon only sputtering gas prefers the formation of AlN ‹100›. Different AlN crystal structure has shown distinct thin film properties and piezoelectric response. This work provides a method to control the crystal structure of the sputter-deposited AlN thin film layer, either c-plane AlN ‹002›, a-plane AlN ‹100› or polycrystalline AlN.

Effect of DC power on opto-thermal properties of AlN thin films

Effect of DC power on opto-thermal properties of AlN thin films

The Influence of Argon Cluster Ion Bombardment on the Characteristics of AlN Films on Glass-Ceramics and Si Substrates.

In this paper, the influence of surface modification on the characteristics and properties of AlN thin films on Si and glass-ceramics substrates is investigated. The surface modification was made at various parameters of argon cluster ions. By using XRD and Raman spectroscopy, it was shown that the obtained AlN films have a hexagonal structure with a characteristic direction of texturing along the c axis and slight deviations from it. A comparison of the AlN surface morphology obtained by atomic force microscopy before and after cluster processing was demonstrated. This demonstrated that the cluster ions with low energy per atom (E/N = 10 eV/atom) have a high efficiency of surface smoothing. A decrease in the intensity of the Raman peaks and an increase in their full-width after bombardment with cluster ions were found, which may be caused by a change in the physicochemical state of the surface. The optical properties, the quality of the boundaries, and the distribution map of the thickness of the functional layer of AlN were investigated by the methods of spectral and spatial resolution ellipsometry. By using the cross-sectional SEM, the direction of crystallite texturing was demonstrated. The influence of argon cluster ion bombardment on the stoichiometry of samples was analyzed by EDX spectroscopy. The results obtained demonstrate the efficiency of the cluster ion smoothing of polycrystalline thin films for microelectronics, particularly when creating surface acoustic wave resonators.

Effects of Argon/Nitrogen Sputtering Gas on the Microstructural, Crystallographic and Piezoelectric Properties of AlN Thin Films

Effects of Argon/Nitrogen Sputtering Gas on the Microstructural, Crystallographic and Piezoelectric Properties of AlN Thin Films

Optical and structural properties of AlN thin films deposited on different faces of sapphire substrates

We report the comprehensive spectroscopic results of AlN thin films deposited on the A-, R- and C-surfaces of sapphire substrates by radio frequency magnetron sputtering. The optical and structural properties of the epitaxial-grown AlN films were characterized using various techniques of high-resolution x-ray diffraction spectroscopy, x-ray photoelectron spectroscopy, Raman scattering spectroscopy, spectroscopic ellipsometry and associated analytical tools. Our large number of measurement results clearly show that sapphire substrates of different polarities have effects on the surface roughness, dislocation density, grain size, microstrain, and surface oxygen binding capacity of the film grown on its surface. The results obtained from Ellipsometry measurements show that the thickness, band gap and roughness of AlN films grown on C-plane sapphire are the smallest among the three samples. After careful analyses of the variable temperature Raman spectra, as the temperature rises from 80 K to 800 K, the AlN film has always exhibited tensile stress. In the same temperature range, the tensile stress of the AlN film grown on the C-plane sapphire has the greatest effect with temperature. The lifetime of E2 (high) phonons gradually decays with the increase of temperature.

The effect of low energy helium implantation on the structural, vibrational, and piezoelectric properties of AlN thin films

Epitaxial AlN thin films were implanted with He at 8 keV along the c-axis growth direction with fluences ranging from 1015 to 1017 atoms/cm2. We find that the He implantation generated uniaxial tensile strain along the c-axis for all fluences that increased with fluence. There was an additional (002) X-ray diffraction peak for the highest He fluences of 5 × 1016 atoms/cm2 and 1017 atoms/cm2 that we interpret in terms of He bubble formation. He implantation leads to significant nitrogen (N) site disorder as evidenced by rapid broadening of the E2 (high) Raman mode with increasing fluence due to a reduction of the phonon mean free path. The piezoelectric coefficient, d33, reduces with increasing fluence, and is ~27% of the unimplanted d33 for the highest fluence. This result can be interpreted as implantation-induced nitrogen site disorder that randomises and reduces the Al–N dipoles. Thus, we show that while He implantation induces uniaxial strain, it decreases d33 due to implantation-induced N site disorder.

Effects of different divalent cations in mTi-based codopants (m = Mg or Zn) on the piezoelectric properties of AlN thin films

The understanding of the effects of different divalent cations in codopants for AlN is important for the design of high-performance AlN-based piezoelectric thin films. The addition of Mg-based codopants (e.g., MgTi) into AlN has been one of the most effective methods for the promotion of a higher piezoelectric response (d33). In this study, Mg was replaced by Zn as the divalent cation in a single dopant or codopant and the effects on the piezoelectric responses were investigated. The substitution of Mg with Zn in a single dopant or codopant affected the crystallinity, composition, and eventually d33 of the thin film.

The composition and interfacial properties of annealed AlN films deposited on 4H-SiC by atomic layer deposition

We have investigated and compared the influence of annealing temperature on composition and interfacial properties of AlN thin films deposited on 4H-SiC substrates by atomic layer deposition using trimethylaluminum (TMA) and ammonia as precursors at 400 °C. Those as-deposited films were annealed by rapid thermal annealing at 700 °C, 800 °C, 900 °C and 1000 °C for 1 min in N2 atmosphere, respectively. As the annealing temperature increased, the thickness of AlN films decreased and the refractive index increased due to the densification and compositional changes in the films. The roughness of films decreased as the films became denser after annealing. In addition, the deposited AlN film is not amorphous structure and the intensity of the (0002) diffraction of the AlN films enhanced in the annealed films. N-O-Al bond broke down and the intensity of Al-N bond increased with the increase of annealing temperature. Moreover, the interface between AlN and SiC was mainly a transition layer containing Al-O-Si, and the intensity of Al-O-Si was enhanced after annealing at 1000 °C. And the annealing process reduced the negative charge and the density of interface trap of the AlN annealed film in the MIS capacitor. These results provide a significant reference for AlN as a gate dielectric for SiC-based MOS devices in the future.

The effect of AlGaAs/GaAs laser heterostructure ionic surface cleaning on the structure and properties of AlN films deposited by the method of reactive ion-plasma sputtering

The paper presents studies of the structural and optical properties of AlN thin films grown on an AlGaAs/GaAs semiconductor laser heterostructure with the use of preliminary ionic surface cleaning and without it. After cleavage of the heterostructure, a natural surface oxide forms on the facet. In the paper, the ionic etching regime providing the removal of the surface oxide layer without significant defects in the semiconductor heterostructure is determined.

Properties of AlN Thin Films on p-Ge Deposited by Thermal Atomic Layer Deposition

The electrical and interfacial properties of atomic layer deposited AlN on p-Ge were investigated. A very large capacitance–voltage (C–V) hysteresis at 1 MHz was observed, resulted from the presence of high density of slow traps that is associated with the GeO volatilization. Nonetheless, well-behaved C–V characteristics with minimal frequency dispersion and the absence of bumps near the flat-band voltage were obtained except 1 MHz, implying that the AlN passivation occurred near the AlN/Ge interface. Parallel conductance values showed that both slow and fast states were located within a narrow energy range. X-ray photoelectron spectroscopy (XPS) spectra revealed that large amount of oxygen atoms are present near the AlN/Ge interface. Above the AlN critical thickness, the strong Al–Al bond in the Al 2p spectra was observed, which could be explained by the strain relaxation due to the lattice mismatch between AlN and Ge.

Surface, structural and optical properties of AlN thin films grown on different face sapphire substrates by metalorganic chemical vapor deposition

AlN thin films grown on different face sapphire substrates by metalorganic chemical vapor deposition were studied comprehensively by a variety of techniques including high resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS) and theoretical calculations. Our results showed that substrate orientation has a drastic effect on the initial growth of AlN. The AlN films showed dominant semipolar (101) orientation but with slightly weaker individual features. Optical reflectance measurements confirmed that AlN films grown on different surface orientation sapphire substrates at the same time possessed different film thicknesses. It was found that the surface orientation also has a major influence on the dislocation density, crystallite size, and surface oxygen incorporation. Raman line width exhibited good correlation with XPS measurements. The combined analyses led to a better understanding of the variation in the quality of the AlN films grown on different faces of sapphires.

RETRACTED: Cross- and in-plane thermal conductivity of AlN thin films measured using differential 3-omega method

Thickness dependency and interfacial structure effects on thermal properties of AlN thin films were systematically investigated by characterizing cross-plane and in-plane thermal conductivities, crystal structures, chemical compositions, surface morphologies and interfacial structures using an extended differential 3ω method, X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy. AlN thin films with various thicknesses from 100 to 1000 nm were deposited on p-type doped silicon substrates using a radio frequency reactive magnetron sputtering process. Results revealed that both the cross- and in-plane thermal conductivities of the AlN thin films were significantly smaller than those of the AlN in a bulk form. The thermal conductivities of the AlN thin films were strongly dependent on the film thickness, in both the cross- and in-plane directions. Both the XRD and AFM results indicated that the grain size significantly affected the thermal conductivity of the films due to the scattering effects from the grain boundary.

Temperature-dependent Optical Properties of AlN Thin Films by Spectroscopy Ellipsometry

In this work, temperature-dependent optical properties of a series of AlN thin films with different thickness are studied by spectroscopic ellipsometry (SE) ranging from 300 to 825K. The fitted refractive index at 300K is in good agreement with the reported by others, which confirms the high accuracy of the optical model used in this work. The degradation of the absorption properties and the decrease of the bandgap become more pronounced with temperature increases above 475K. A larger change of bandgap at elevated temperature is observed for the thinner AlN epi-layer (300nm) than the thicker ones (404nm). This can be attributed to the poor surface morphologies and crystal qualities in the thinner AlN epi-layer.

Theoretical investigation of the electronic and structural properties of AlN thin films

Studying the electronic and structural properties of AlN thin films is an important problem because such films are widely used as a buffer layer when growing GaN-based semiconductor heterostructures on Si substrates. In this paper, we carry out a theoretical investigation of the properties of an Al-terminated AlN(0001) surface in the framework of the density functional theory. Ab initio calculations allow us to analyze the effect of the in-plane lattice strain on the energy of this surface. It is shown that compressive strain causes a decrease in the AlN(0001) surface energy, while tensile strain leads to its increase. Knowing the surface energy values allows us to evaluate the stress of the surface under investigation. In addition, the curvature of the AlN surface is calculated for various AlN film thicknesses in the case of free growth. The obtained values of the surface curvature are in close agreement with the known experimental results.

Properties of AlN thin films deposited by means of magnetron sputtering for ISFET applications

AbstractThis work presents the investigations of AlN thin films deposited on Si substrates by means of magnetron sputtering. Nine different sputtering processes were performed. Based on obtained results, the tenth process was prepared and performed (for future ISFET structures manufacturing). Round aluminum (Al) electrodes were evaporated on the top of deposited layers. The MIS capacitor structures enabled a subsequent electrical characterization of the AlN films by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements. Based on these results, the main parameters of investigated layers were obtained. Moreover, the paper describes the technology of fabrication and electrical characterization of ISFET transistors and possibility of their application as ion sensors.

Research on the Piezoelectric Properties of AlN Thin Films for MEMS Applications

In this paper, the piezoelectric coefficient d33 of AlN thin films for MEMS applications was studied by the piezoresponse force microscopy (PFM) measurement and finite element method (FEM) simulation. Both the sample without a top electrode and another with a top electrode were measured by PFM to characterize the piezoelectric property effectively. To obtain the numerical solution, an equivalent model of the PFM measurement system was established based on theoretical analysis. The simulation results for two samples revealed the effective measurement value d33-test should be smaller than the intrinsic value d33 due to the clamping effect of the substrate and non-ideal electric field distribution. Their influences to the measurement results were studied systematically. By comparing the experimental results with the simulation results, an experimental model linking the actual piezoelectric coefficient d33 with the measurement results d33-test was given under this testing configuration. A novel and effective approach was presented to eliminate the influences of substrate clamping and non-ideal electric field distribution and extract the actual value d33 of AlN thin films.

Role of oxygen contaminant on the physical properties of sputtered AlN thin films

The paper deals with the role of the oxygen contamination, coming from residual gas atmosphere in the deposition chamber, on the physical properties of AlN thin films, sputtered in Ar + N2 working gas, at different values of nitrogen flux percentages, and without substrate heating. Contaminant concentration varies with the nitrogen partial pressure in the working gas mixture. Oxygen atoms are incorporated into the growing films due to their higher affinity towards Al atoms compared to N atoms. Oxygen inclusion produces important modifications in the structural, chemical, optical and electrical properties of the AlN thin films. Therefore, contamination can play a crucial role for the tuning of the physical characteristics of sputtered materials.

Electric and pyroelectric properties of AlN thin films deposited by reactive magnetron sputtering on Si substrate

Electric and pyroelectric properties of AlN layers deposited on Si substrates with different resistivities were investigated. The dielectric constant was found to be around 12, while the conductance determined from dc current measurements was found to be in the 10−9 to 10−10S range. The pyroelectric measurements were performed in voltage mode using two types of IR sources: a laser diode with 800nm wavelength and a black body at 700°C. A peculiar behavior was observed for the signal recorded when the laser diode was used as IR source. It was found that the Si substrate is introducing a signal component, due to the photogenerated carriers, which is adding to the pyroelectric signal generated by the AlN layer. This component is strongly dependent on the resistivity of the Si substrate. For strongly doped Si (Si++) the signal generated into the substrate represents only 10% of the recorded pyroelectric voltage. For electronic grade Si the signal generated into the substrate is about 100 times larger than the pyroelectric signal generated in the AlN layer. This effect can be used as an optical amplification of the pyroelectric signal. The frequency dependence observed for the pyroelectric signal recorded when the black body is used as IR source is typical for a pyroelectric detector. A value as large as 12.4μCm−2K−1 was obtained for the pyroelectric coefficient using for estimation the constant signal at low modulation frequencies of the IR beam. However, the value of the pyroelectric coefficient is strongly affected by the electrical conductance of the AlN layer. As the conductance is frequency dependent it results that the value of the pyroelectric coefficient is frequency dependent, the value from above being valid only for very small frequencies of the temperature variation. It was also found that the electric and pyroelectric properties are dependent on the crystalline quality of the AlN layer.

Theoretical Investigation of Electronic and Structural Properties of AlN Thin Films

Study of the electronic and structural properties of AlN thin films is an important problem because these films are widely used as buffer layers for GaN − based semiconductor heterostructures growth on Si substrates. In this paper we performed a theoretical investigation of the properties of Al − terminated AlN(0001) surface in the framework of density functional theory. Ab initio calculations allowed us to study the impact of in − plane lattice strain on the surface energy of this surface. We show that the presence of the compressive strain leads to a decrease of the AlN(0001) surface energy while tensile strain increases the surface energy of this surface. Surface energy values allowed us to calculate the stress value of the surface under investigation. Also we calculated the curvature of the AlN surface as a function of film thickness for free growth. The resultant curvature values are in a good agreement with known experimental results.

Effect of annealing on the structural properties of AlN thin films containing Co particles

This paper describes a new approach for preparing AlN thin films containing various Co contents by using a two-facing targets type sputtering system. The as-deposited films exhibited a variable nature expected from the AlN-rich phase, as well as an amorphous-like phase, depending on the Co content in the films. The films were annealed isothermally at different temperatures and their microstructure, magnetic properties and resistivity were examined. The saturation magnetization of the as-deposited films was quite small and almost constant, irrespective of the Co content in the films, because Co was not in the crystalline state. At elevated annealing temperatures, the as-deposited AlN-Co amorphous films crystallized into two phases of AlN and Co. The saturation magnetization and resistivity of the films increased with increasing annealing time and temperature. The coercivity of the films was independent of the annealing time, but it increased with increasing annealing temperature due to the increase in grain size. A saturation magnetization, coercivity and resistivity of 360 emu/cm3, ∼25 Oe and 2200 μΩ-cm, respectively, were obtained. Further improvement in the soft magnetic properties might lead to this material being applied as a high density magnetic recording head material.