Combinatorial Pulsed Laser Deposition Technique Research Articles

Combinatorial tuning of structure and optoelectronic properties of Zn-Ga-O thin films for deep ultraviolet photodetection

Ternary complex oxides exhibit strong compositional dependence on their structure and functionalities. While the profound impact of the cation stoichiometry on the physical properties of ZnGa2O4 is widely recognized, how it affects the ultraviolet photodetection behavior remains not clear. Here we apply a combinatorial pulsed laser deposition technique to establish graded composition in ZnxGa1-xO (0 ≤ x ≤ 1) across a 2-inch sapphire substrate. In combination with structural and optical characterizations, a systematic investigation of the compositional effect on the phase, crystallinity and bandgap for the ZnxGa1-xO system is performed, and their further impact on the photodetection performance is compared by fabricating multiple metal–semiconductor-metal (MSM) photodetectors based on the graded ZnxGa1-xO films. Decent photodetection behavior is seen for the photodetectors with x ≤ 0.33, above which the performance is largely limited by the conductive phase formation. An optimized compositional range of x = 0.18–0.27 is identified to deliver the best device performance, which includes a responsivity of 12.88 A/W and a photo-to-dark current ratio of 2.8 × 108. This slight zinc deficiency is considered beneficial for the formation of moderate level of oxygen vacancies or antisite defects that boosts carrier transport. This study sheds light on the composition-dependent evolution of structure and properties in ternary ultrawide-bandgap semiconductors for high-performance ultraviolet photodetection.

Quantitative analysis of amorphous indium zinc oxide thin films synthesized by Combinatorial Pulsed Laser Deposition

The use of amorphous and transparent oxides is a key for the development of new thin film transistors and displays. Recently, indium zinc oxide (IZO) was shown to exhibit high transparency in the visible range, low resistivity, and high mobility. Since the properties and the cost of these films depend on the In/(In + Zn) values, the measurement of this ratio is paramount for future developments and applications. We report on accurate analysis of the elemental composition of IZO thin films synthesized using a Combinatorial Pulsed Laser Deposition technique. The monitoring of the thin films elemental composition by Laser-Induced Breakdown Spectroscopy was chosen in view of further in situ and real-time technological developments and process control during IZO fabrication. Our analytical approach is based on plasma modeling, the recorded spectra being then compared to the spectral radiance computed for plasmas in local thermal equilibrium. The cation fractions measured were compared to values obtained by complementary measurements using energy dispersive X-ray spectroscopy and Rutherford backscattering spectrometry. Spectroscopic ellipsometry assisted the scientific discussion. A good agreement between methods was found, independently of the relative fraction of indium and zinc that varied from about 65 to 90 and 35 to 10 at%, respectively, and the measurement uncertainties associated to each analytical method.

Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0)Si and quartz substrates that were heated at temperatures from 300 to 500 °C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture.

Microstructural Investigations of Hafnium Aluminum Oxide Films

ABSTRACTThe crystalline structure, composition, chemical bonding and thermal stability of HfO2-Al2O3 mixtures deposited on Si using a combinatorial pulsed laser deposition technique were investigated. After deposition some films were annealed at temperatures from 850 to 950 °C for 6 or 12 minutes. Grazing incidence x-ray diffraction investigations were performed to asses the crystallinity and thermal stability of the annealed layers. Measurements of the Al to Hf ratios were performed using energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. From simulations of the x-ray reflectivity and spectroscopic ellipsometry spectra the phase composition and thickness of the films was calculated and then the Al to Hf ratios. Al/Hf values of 1 and 8 were found to be necessary to block the crystallization of the films after anneals at 850 and 950 °C, respectively.

Comparative studies of transparent conductive Ti-, Zr-, and Sn-doped In2O3 using a combinatorial approach

We report on comparative studies of transparent conductive Ti-, Zr-, and Sn-doped In2O3 using a combinatorial approach. In2−2xMe2xO3 (Me:Ti, Zr, Sn) composition-spread epilayers (0≤x≤0.1) were fabricated on yttria-stabilized zirconia substrates using the combinatorial pulsed laser deposition technique, and structural, optical, and electrical properties for each composition were systematically investigated. In2−2xTi2xO3 (0.003≤x<0.01) and In2−2xZr2xO3 (0.003≤x<0.05) exhibited superior transparency in the near infrared wavelength region compared to In2−2xSn2xO3 without compromising the conductivity. The results are discussed in terms of scattering centers of electrons from temperature dependence of Hall mobility and the relationship between the values of the room temperature Hall mobility and carrier concentration.

Combinatorial synthesis of Li-doped NiO thin films and their transparent conducting properties

Transparent and conductive oxide (TCO) thin films of Li-doped NiO were prepared by combinatorial pulsed laser deposition technique. Composition spread approach was applied to optimize the Li concentration for achieving high conductivity and transparency in the film. Conductivity of the composition spread film was found to increase almost linearly from nearly insulating to as high as 1.41 Ω −1 cm −1 with increasing Li content along a 9 mm long film. Optical transparency was found to decrease in an equal proportion across the 40 nm thick film with a slight shift in the absorption edge.

Combinatorial screening of ternary NiO–Mn2O3–CuO composition spreads

We describe the screening of large combinatorial oxide libraries for their electric transport characteristics. Complete ternary composition spreads of NiO–Mn2O3–CuO oxide alloys were deposited onto conducting Nb-doped SrTiO3 substrates using the combinatorial pulsed laser deposition technique. Resistance-temperature relations for each composition in the spread were determined using a custom-designed scanning probe. Ternary and binary electrically conducting alloys are located around Ni0.45Cu0.75Mn1.65O4 (the lowest resistance point) and CuMn2O4 compositions, respectively. The temperature sensitivities of the compositions Ni0.3Cu0.3Mn2.4O4,Cu0.84Mn2.16O4, and Cu1.35Mn1.65O4 were 5.0%/°C, 3.5%/°C, and 3.0%/°C, respectively. From this screening we propose compounds for thin-film negative temperature coefficient thermistors with standardized characteristics.

Quick optimization of Y-type magnetoplumbite thin films growth by combinatorial pulsed laser deposition technique

Quick growth optimization of complex oxide, Y-type magnetoplumbite (Ba 2Co 2Fe 12O 22 (Co 2Y)) thin films is demonstrated by using combinatorial thin film technology. Planning a CoO buffer layer on MgAl 2O 4(1 1 1) substrate was found to be very effective for preventing the phase separation of Co deficient impurity (BaFe 2O 4) and forming the desired Co 2Y phase. The combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction facilitate the production of Y-type magnetoplumbite thin film in a single phase.

Characterization of Magnetic and Dielectric Properties on Y-Type Magnetoplumbite Epitaxial thin Films for High Frequency Application

AbstractMagnetic films for miniaturization of planar inductors operating at GHz frequencies require high resistivity and high ferro-magnetic resonance frequency. Y type magnetoplumbite Ba2Co2Fe12O22(Co2Y) is a candidate material to meet such requirements because it has about 10 &m resistivity and resonance frequency higher than 2 GHz. Recently we succeeded in the fabrication of Co2Y epitaxial thin film on MgAl2O4 substrate by combinatorial pulsed laser deposition technique [3]. Here, we report on the magnetic and dielectric properties of this film. The DC resistivity of the film was 7.5 &m. The dielectric constant at 1.25 GHz was measured by a microwave microscope to be 11.0. An easy axis coercive force and saturation magnetization were about 145 Oe and 2000 Gauss respectively, being close to those of bulk sample. Furthermore, the magnetic micro domain structures of Co2Y epitaxial thin films were observed by a scanning SQUID microscope.