Aluminum Zinc Oxide Thin Films Research Articles

Epitaxial growth of ZnO thin films on AlN substrates deposited at low temperature by magnetron sputtering

AbstractHexagonal aluminium nitride (AlN) and zinc oxide (ZnO) thin films have been deposited by DC and RF reactive magnetron sputtering at room temperature. For a first set of samples, sputtered AlN films were deposited on silicon ZnO substrate. For a second set, ZnO films were deposited on AlN substrate. X‐ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analysis of the synthesized AlN film on ZnO buffer layer have shown some amorphous zones close to the interface followed by a nanocrystalline layer exhibiting (10−10) and (0002) orientations of the hexagonal AlN crystalline phase. At the top of the film, a relatively well‐crystallized layer with a single (0002) orientation has been observed. We have related the relatively bad interface to the presence of oxygen coming from ZnO substrate. This behaviour was different for the growth of ZnO film when AlN was used as substrate. In fact, we have observed thanks to HRTEM images and selected area electron diffraction patterns, that the ZnO film deposited on AlN substrate exhibits an epitaxial growth which is strongly dependent on the crystalline quality of AlN film.

Effect of deposition temperature on the properties of nitrogen-doped AZO thin films grown on glass by rf reactive magnetron sputtering

Abstract Nitrogen-doped aluminum zinc oxide (NAZO) thin films were deposited on glass substrates at various deposition temperatures by rf reactive magnetron sputtering. The NAZO film deposited at 400 °C shows a strongly c -axis preferred orientation and n-type conduction with a resistivity of 2.1 × 10 −2 Ω cm, Hall mobility of 7.7 cm 2 V −1 s −1 , and electron concentration of 3.8 × 10 19 cm −3 . The optimum crystallographic structure occurs at a deposition temperature of 400 °C, where a considerable crystallinity enhancement of the films is observed. The band gap energies of the NAZO films, obtained by using Tauc model and parabolic bands, are found to significantly depend on the deposition temperature, along with the band gap narrowing at higher deposition temperature due to renormalization effects.

Nanoscale surface electrical properties of aluminum zinc oxide thin films investigated by scanning probe microscopy

Conducting atomic force microscopy and scanning surface potential microscopy were adopted to study the nanoscale surface electrical properties of aluminum zinc oxide (AZO) films that were prepared by pulsed laser deposition (PLD) at various substrate temperatures for use as anode materials in polymer light-emitting diodes (PLEDs). Experimental results indicate that when substrate temperatures exceed 100°C, the local conductivity and work function are positively correlated with the concentrations of Al dopant and O2− on AZO surface. When the substrate temperature is approximately 150°C, the percentage coverage of conducting regions of the AZO surface and the mean work function are 90.20% and 4.85eV, respectively. Additionally, both microcosmic uniformities meet the standard applied to PLEDs. This low-temperature condition for PLD significantly reduces the yield rate of impurities when AZO vacuum evaporation is performed on a plastic substrate, supporting various applications of AZO films.

ANNEALING EFFECTS ON CONTACT PROPERTIES OF ALUMINUM DOPED ZINC OXIDE THIN FILMS

Aluminum Zinc Oxide (AZO) thin films are grown on glass substrates by RF Magnetron Sputtering using a single target of zinc oxide (99 wt%) and aluminum oxide (1 wt%) with argon as the plasma. Photolithographic process is then performed on the films in order to obtain a Transmission Line Model structure (TLM) of the metal contact system, namely aluminum and gold. The specific contact resistivity, ρc, of these two metal-semiconductor systems, which will undergo different rapid thermal annealing (RTA) environment, are determined. X-Ray diffraction patterns for these samples are obtained to investigate phase formations or micro-structural changes so as to justify for the differences in specific contact resistivity obtained for these contact systems. The different RTA environment are simulated by purging either nitrogen or argon gas, with a pressure of 40 psi at a temperature of 400°C for 60 s; and annealing in vacuum (10-6 Torr) also at the same temperature and duration. One-dimensional TLM (1D-TLM) measurements are performed on the TLM structures to obtain the specific contact resistivity, ρc. Results show that aluminum contacts on AZO without RTA give the lowest ρc as compared to those in other environment, while gold contacts on AZO annealed in vacuum yield the lowest ρc. Adhesion of aluminum contacts on AZO is good even when subjected to ultrasonic bath test but not true for the case of gold contact, which adheres poorly on AZO films.

DC reactive sputter deposition of ZnO:Al thin film on glass

Common semiconducting metal oxide thin films include ITO (indium–tin oxide) thin films, ATO (aluminum–tin oxide) thin films, and AZO (aluminum–zinc oxide) thin films. Recently, increasing research interest on the AZO thin films is not only due to the low resistivity, but also the optical characteristics. AZO thin film exhibits a sharp UV cut-off and a high refractive index in the IR range, and is transparent in the visible light. The objective of this study was then to investigate the electrical and optical properties of AZO as a function of various growth parameters, including target composition, O 2/Ar ratio, and applied power. The crystal structure was found to be insensitive to oxygen partial pressure but affected by the doping of Al. However, the values of resistivity depend on both the oxygen partial pressure and the Al doping level.

Synthesis and characterization of zinc aluminum oxide thin films by sol–gel technique

Crack free, and dense ZnAl 2 O 4 thin films have been prepared by a sol–gel method using aluminum sec -butoxide and zinc acetate. The complete single phase cubic structure of ZnAl 2 O 4 was formed on a silicon (1 0 0) substrate at an annealing temperature of 700°C for 5 h. As the annealing temperature increased from 700 to 800°C, we did not observe any kind of diffusion of Si in the formation of silicate phase at the interface of Si and ZnAl 2 O 4 phase as observed by grazing angle XRD. Structural, morphological and elemental evolution of these ZnAl 2 O 4 thin films produced by sol–gel synthesis were characterized by grazing incidence X-ray diffraction (GIXRD), tapping mode atomic force microscopy (TMAFM), and X-ray photoelectron spectroscopy (XPS), respectively.

Piezoelectric films for 100-MHz ultrasonic transducers

Piezoelectric aluminum nitride (AlN) and zinc oxide (ZnO) thin films were deposited by reactive magnetron sputtering for use in ultrasonic transducers in the 100- to 300-MHz regime. Pulse-echo ultrasonic transducers are being developed to image subsurface microstructure in metal and non-metal (ceramic) materials and components. A Krimholtz, Leedom, Matthaei (KLM) model was used to aid in the design of the ultrasonic transducer. Design criteria included piezoelectric material properties and thickness, electrode material and thickness, substrate dielectric properties, active area diameter and bandwidth and sensitivity requirements. The preliminary designs consisted of Ni/AlN/Ni and Ni/ZnO/Ni on BK-7 glass and fused silica substrates. AlN was chosen because of its a high longitudinal wave velocity of 10 700 m/s and high dielectric strength of 20 MV/cm. Strongly oriented (002) AlN and ZnO coatings, up to 50 μm thick, were deposited onto transducer substrates. Transducers with strongly oriented (002) crystal orientation displayed the highest longitudinal/shear (L/S) wave ratio of 19.6 dB. Crystalline structure was found to depend primarily on substrate temperature, substrate placement, and substrate material. Substrate temperatures ranged between 100 and 400°C. Strongly (002) oriented AlN films were deposited at substrate temperatures as low as 100°C. The L/S ratio decreased with the onset of the (103) and other crystal orientations, which resulted from off-normal adatom flux incidence during deposition. Near normal incidence flux angles were needed to obtain the (002) crystal orientation. Substoichiometric ZnO films were obtained at substrate temperatures below 300°C. The transducers operated at frequencies between 50 and 100 MHz, with performance very close to that of the design.

Influence of the doping and annealing atmosphere on zinc oxide thin films deposited by spray pyrolysis

Undoped and doped (indium and aluminium) zinc oxide (ZnO) thin films have been prepared by spray pyrolysis, and the effect of the doping and annealing atmosphere on the electrical, optical and structural properties of the produced films has been investigated. The deposited films have a high resistivity. Annealing the films in an argon atmosphere or under vacuum leads to a substantial reduction of the electrical resistivity of the films and to an increase on the degree of cristallinity of the deposited material. The most pronounced changes were observed in the films annealed in Argon. The results also indicate that doping highly influences the electrical and structural properties of the films, which is more pronounced in the films doped with Indium.