Aluminum Nitride (AlN) is a technologically important wide band gap semiconductor and a potential piezo-electric material for Biosensor application [1]. It is a clear candidate for the integration of surface acoustic wave (SAW) devices on chips with silicon-based electronics [2]. AlN may also prove to be useful for the integration of mechanical devices and also in the field of packaging of Bio-MEMS devices because of its superior thermal conductivity 130-140 (W/mK, room temp-100 deg C) and nontoxicity. In the current work an attempt has been made to determine the elastic modulus of AlN coated on Si-microcantilevers, employing the concept of symmetrically laminated beam theory for the first time at the micro level thus avoiding the coupling effects. So far the earlier studies have been done only using simple beam theory. Modal vibration frequencies for microcantilevers without and with the AlN coating were used, along with analytical models and knowledge of the Si modulus, to “back out” the modulus of AlN [3].

Pb1-x Srx TiO3 (x = 0 to 1.0) films of thickness ∼ 4 μ m have been prepared on sapphire and Pt substrates by metalorganic decomposition (MOD) method. X-ray diffraction results show that the films are polycrystalline with a perovskite tetragonal phase at room temperature for x < 0.5 and a cubic phase for x > 0.5. Room temperature Raman spectra show a systematic variation of lattice vibrational modes with x. The most notable changes in the Raman spectra with x are the decrease in the splitting of A1(3TO) and E(3TO) modes and the disappearance of E(3TO) mode at x ∼ 0.6. Although the x-ray diffraction peaks for films with x > 0.5 show a cubic phase at room temperature, the Raman spectra show the characteristic phonon modes of a tetragonal phase even at x = 0.7. The dielectric permittivity versus temperature measurements for films with x ≤ 0.7 show a broad dielectric anomaly corresponding to a diffuse ferroelectric to paraelectric phase transition. The phase transition temperature (Tc) values are consistently lower than the corresponding bulk ceramic alloys. Furthermore, Tc are also determined by monitoring the temperature dependence of the splitting between E(3TO) and A1(3TO) phonon modes in the Raman spectra of Pb1-x Srx TiO3 films for x ≤ 0.6. There has been good agreement between the two methods.

The optical and electrical properties of InN films with different levels of carrier concentrations have been investigated. Hall effect measurements at room temperature show that the InN films are n-type with carrier concentration, ne, ranging from ∼ 7 ×1017 cm-3 to ∼ 3 × 1020 cm-3 and corresponding mobility, //, of ∼ 1300 to 50 cm2V-1S-1. Optical absorption spectra of these films show a bandgap absorption edge ∼ 0.6 eV for the InN sample with the lowest ne, and 1.5 eV for the InN sample with the highest ne. However, after corrections for the degeneracy effects, all samples show an intrinsic Eg ∼ (0.60 ± 0.05) eV. Temperature dependent (5 – 600 K) electrical measurements show that ne is nearly independent of temperature below 300 K, perhaps due to the presence of donor energy levels resonating with the InN conduction band. However, all the samples show an exponential increase in ne above 300 K due to excitation of other shallow donor like sources. Mobility versus temperature graph shows a maximum ∼ 200 K for InN film with ne = 7 × 1017 cm-3 and moves towards lower temperature with increasing ne.

Polarization-graded ferroelectrics and their electrically active counterparts, graded ferroelectric devices (GFDs) and transpacitors has been achieved in a number ways, including a variation in the composition of the material, or impressing a temperature gradients across the structure. In this article, we report how these same devices can be formed from homogeneous ferroelectric films of lead strontium titanate by imposing stress gradients on the materials normal to their electrode surfaces. A qualitative description of asymmetric hysteresis behavior based on a modified Landau potential is provided.

Anatase (A), rutile (R) and amorphous phase TiO2 thin films have been prepared by RF magnetron sputtering on unheated glass substrates by controlling the total pressure of sputtering gases (Ar + O2) and the substrate bias. The crystal structures of the films were confirmed by x-ray diffraction and Raman scattering. The analysis of optical absorption data for A- TiO2 film shows an energy bandgap (Eg) of 3.2 eV (indirect extrapolation) and ∼ 3.5 eV (direct extrapolation). On the other hand, R-TiO2 film shows Eg ∼ 2.9 eV (indirect) and 3.2 eV (direct). The latter film also shows the presence of amorphous regions with Eg ∼ 3.0 eV (indirect) and 3.8 eV (direct). The bandgap of both the films, obtained using indirect extrapolation, has a value range consistent with the previous measurements.

The optical properties of InN thin films (0.5 μm thick) grown on sapphire substrates by plasma source molecular beam epitaxy deposition have been measured in order to study the effect of electron degeneracy on the band gap measurement. X-ray diffraction measurements show that the films are wurtzite polycrystalline at a growth temperature of 325 °C, whereas a completely c-axis textured growth at a temperature of 475°C. The Raman bands A1 (LO) and E2 are rather broad indicating the presence of a large number of structural defects. Hall effect measurements show that both the films are n-type with carrier concentrations of (8.0 ± 1.6) × 1020 cm−3 and (3 ± 0.6) × 1020cm−3, respectively. The optical absorption data on these samples show n dependent band gap edge and a peak corresponding to plasmon due to strong electron degeneracy. The band gap absorption data were analyzed assuming a direct band gap and incorporating the Moss-Burstein shift effect. By taking into account the non-parabolic dispersion and the band-renormalization effects for the conduction band of InN, the calculated true band gap (0.7 eV) agrees with other recent measurements on high quality InN films.

Infrared (IR) spectroscopy and ultraviolet near-resonance enhanced Raman scattering have been used as alternative techniques to characterize the AlN films grown on Si(111). Epitaxial AlN films have been prepared by plasma source molecular beam epitaxy (PSMBE) at growth temperatures of 400 and 650 oC. The AlN/Si grown at 650°C shows distinct reflection high-energy electron diffraction (RHEED) patterns with the following epitaxial relations: AlN [0001] ‖ Si [111], and AlN < 011 0 > ‖ Si < 112 >. This is in sharp contrast with the observation of a spotty RHEED pattern for AlN/Si sample grown at 400°C, which appeared the same when viewed along any Si azimuth. Furthermore, the X-ray diffraction (XRD) rocking curve width showed a significant reduction from 5.7ofor sample grown at 400°C to 2° for the one grown at 650°C. The observation of Raman active A1(LO) and E2, and IR active E1(TO) zone center phonons, in both the films, is in accordance with the c-axis orientation of the films. However, the observed phonon mode frequencies and line widths indicate that the AlN samples grown at 400°C have less strain but more disorder compared to the ones grown at 650°C in agreement with RHEED and XRD data.

An alternate array of Pd/AlN/Si and Al/AlN/Si metal-insulator-semiconductor (MIS) devices has been developed using plasma source molecular beam epitaxy (PSMBE) method for deposition of AlN on Si and magnetron sputtering for deposition of Pd and Al electrodes (via mask) on AlN. Both devices show essentially identical capacitance (C) versus voltage (V) characteristics of the typical MIS capacitor. However, the C-V characteristic of a Pd-device shows a clear shift in the presence hydrogen, while that of an Al-device shows no shift. These sensors were characterized using C(V) and C(time) measurements under varying hydrogen concentration. The effects of oxygen and hydrocarbon gases on the sensors were also studied. The Pd-device responds selectively to hydrogen. These results suggest the possibility of fabricating a balanced sensor structure, which might have significant practical importance, as it would cancel all thermal and material sources of drift in the electrical component of the sensor response.

An AlN (insulator) MIS Hydrogen Sensor was created using plasma source molecular beam epitaxy (PSMBE) deposition on Si (111) and 6H-SiC. A Pd layer was deposited on top of the AlN film via magnetron sputtering technique utilizing a hard mask. Pd was chosen since H2 readily diffuses within its bulk, thus Pd acts not only as a metal electrode of the MIS structure, but also as a catalyst for hydrogen dissociation. To optimize the design structure several sensors with different AlN and Pd thickness have been developed. RHEED and XRD measurements show that AlN film is epitaxial on both Si (111) and 6H-SiC substrates. The sensors were characterized using capacitance versus voltage C(V) and I(V) measurements, at different frequencies ranging from 1kHz to 1 MHz. Shifts in the C-V and I-V curves occurred with the introduction of hydrogen in the chamber. The temperature, hydrogen partial pressure, effects of oxygen and hydrocarbon gases, insulator and metal thicknesses on sensor response were analyzed.

Epitaxial Al1−xInxN films (thickness ∼150 nm) with 0 ≤ × ≤ 1 have been grown by Plasma Source Molecular Beam Epitaxy on Sapphire (0001) at a low substrate temperature of 375°C and were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), and atomic force microscopy (AFM). Both RHEED and XRD measurements confirm the c-plane growth of Al1-xInxN films on sapphire (0001) with the following epitaxial relations: Nitride [0001] ∥ Sapphire [0001] and Nitride < 0110 > ∥ Sapphire <2110>. The films do not show any alloy segregation. However, the degree of crystalline mosaicity and the compositional fluctuation increases with increasing In concentration. Further, AFM measurements show an increased surface roughness with increasing In concentration in the alloy films.

A series of epitaxial InxAl1−xN alloy films (thickness ~ 150 nm) with 0 ≤ × ≤ 1.0 were grown by Plasma Source Molecular Beam Epitaxy (PSMBE) on sapphire (0001) at a low substrate temperature of 375 °C. X-ray diffraction (XRD) measurements confirm a c-axis oriented epitaxial growth of alloy films without any alloy segregation. However, the degree of crystalline mosaicity, compositional fluctuation and surface roughness, all increase with increasing x. The direct energy band gap of alloy films were determined using optical (UV-VIS) transmission and reflection measurements. The observed bowing of the direct gap versus x plot, when compared to the theoretical prediction, is less pronounced than seen in earlier studies reported in literature. Electrical resistivity and Hall effect measurements show n-type electrical conductivity in these alloys with carrier concentrations ~1019-1020 cm−3 for x > 0.5.

AIN/SiC structures are of current importance for the development of high temperature electronic devices. A systematic study of the growth and structure of AIN on Lely grown 6H-SiC was performed. The SiC substrates were chemically etched followed by thermal desorption at 875 °C under UHV conditions. AFM and RHEED images show the relative improvement in surface morphology following the cleaning procedure. AIN films were grown on 6H-SiC substrates using plasma source molecular beam epitaxy (PSMBE). Substrate temperatures were varied from 400 °C to 800 °C and deposition energies from 1 eV to 25 eV during AIN growth. The AIN crystal structure and topology were analyzed by RHEED and AFM. The AIN/SiC film microstructure are correlated with the quality of the SiC surface and the parameters of the AIN deposition process. Epitaxial growth of AIN(0002) was strongly dependent on the SiC surface quality and deposition energy. The highest quality AIN was achieved at growth temperatures of approximately 600 °C and 15 eV ion energy. Higher ion energy resulted in amorphous film growth.

AIN films were grown on Si (111) substrates using a PSMBE deposition system. Two types of growth methods were used: (i) a continuous growth at one temperature and (ii) a two stage growth where a buffer layer at low temperature is followed by deposition at higher temperature. The structure and morphology of the films grown at different temperatures are compared. The evolution of surface structure and morphology of the film during the growth were studied using in-situ RHEED, X-ray diffraction, and AFM.

Reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD) studies on Ag and Au films grown on hydrogen terminated Si(111) substrates at room temperature indicate a <111> oriented growth. Atomic force microscopy (AFM) data reveal a smooth surface morphology for both Ag and Au films after annealing at 275°C and 175°C for 1 hour, as compared to films without annealing. High resolution transmission electron microscopy (HREM) was employed to examine the annealed samples. HREM studies show a highly uniform film with abrupt interface for Ag/Si(111). On the other hand, Au/Si(111) shows several twin formations both at the interface and in the bulk of the film.