M. K. Jayaraj

Transparent p-type conducting CuScO2+x films

Transparent films of CuScO2+x have been prepared which show p-type electrical conductivity. The temperature dependence of the conductivity indicates semiconducting behavior with an apparent room temperature activation energy of 0.11 eV. The highest room temperature conductivity observed was 30 S cm−1. Films 110 nm thick show 40% transparency in most of the visible spectrum and become much more transparent in the infrared spectrum. The p-type behavior was confirmed by the Seebeck effect.Transparent films of CuScO2+x have been prepared which show p-type electrical conductivity. The temperature dependence of the conductivity indicates semiconducting behavior with an apparent room temperature activation energy of 0.11 eV. The highest room temperature conductivity observed was 30 S cm−1. Films 110 nm thick show 40% transparency in most of the visible spectrum and become much more transparent in the infrared spectrum. The p-type behavior was confirmed by the Seebeck effect.

p-Type oxides for use in transparent diodes

Several p-type oxides of the delafossite structure have been investigated in the hope that the conductivity and transparency will be high enough to render them useful in the manufacture of transparent p–n junction diodes and other transparent devices. The highest conductivity achieved to date has been 220 S/cm in CuCr1−xMgxO2 thin films. Oxygen intercalation in CuSc1−xMgxO2+y films improves the conductivity at the expense of optical transparency. We have improved the conductivity of CuGaO2-based films from 0.02 to 1 S/cm by substitution of Fe for Ga. p-Type conductivity has been demonstrated in an Ag-based delafossite film. A sputter-deposited AgCoO2 film has a conductivity of 0.2 S/cm, a Seebeck coefficient of 230 μV/K and a band gap of 4.1 eV at room temperature. CuNi2/3Sb1/3O2 films have been produced that are p-type conductors when doped with Sn.

Transparent conducting zinc oxide thin film prepared by off-axis rf magnetron sputtering

Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm-1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.

Optical and electrical properties of amorphous zinc tin oxide thin films examined for thin film transistor application

Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure (PO2) used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films [Chiang et al., Appl. Phys. Lett. 86, 013503 (2005)], the PLD-deposited films crystallized at a lower temperature <450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps (Tauc gaps) were 2.80−2.85 eV and almost independent of oxygen PO2, which are smaller than those of the corresponding crystals (3.35−3.89 eV). Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low PO2<2 Pa ...

Electrical characterization of transparent p - i - n heterojunction diodes

Transparent p–i–n heterojunction diodes are fabricated using heavily doped, p-type CuYO2 and semi-insulating i-ZnO thin films deposited onto a glass substrate coated with n-type indium tin oxide. Rectification is observed, with a ratio of forward-to-reverse current as high as 60 in the range −4–4 V. The forward-bias current–voltage characteristics are dominated by the flow of space-charge-limited current, which is ascribed to single-carrier injection into the i-ZnO layer. Capacitance measurements show strong frequency dispersion, which is attributed to i-ZnO traps. The diode structure has a total thickness of 0.75 μm and an optical transmission of ∼35%–65% in the visible region.

Synthesis of ZnO nanoparticles by hydrothermal method

Stable, OH free zinc oxide (ZnO) nanoparticles were synthesized by hydrothermal method by varying the growth temperature and concentration of the precursors. The formation of ZnO nanoparticles were confirmed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The average particle size have been found to be about 7-24 nm and the compositional analysis is done with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Diffuse reflectance spectroscopy (DRS) results shows that the band gap of ZnO nanoparticles is blue shifted with decrease in particle size. Photoluminescence properties of ZnO nanoparticles at room temperature were studied and the green photoluminescent emission from ZnO nanoparticles can originate from the oxygen vacancy or ZnO interstitial related defects.

Optical and Carrier Transport Properties of Cosputtered Zn–In–Sn–O Films and Their Applications to TFTs

The optical and carrier transport properties of amorphous transparent zinc indium tin oxide ZITOa-ZITO thin films and the characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films were very conductive and showed clear free carrier absorption FCA. The analysis of the FCA gave the effective mass value of 0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing the Zn content, while large on‐off current ratios 10 7 ‐10 8 were kept for all the Zn contents. The field effect mobilities ranged from 12.4 to 3.4 cm 2 V

Host Sensitized White Luminescence from ZnGa2O4 : Dy3 + Phosphor

Dysprosium-doped zinc gallate phosphors with the nominal formulas ZnGa 2(1-x) O 4 :Dy 2x were prepared by the high-temperature conventional solid-state reaction technique, the dopant concentration being varied in the range 0 ≤ x ≤ 0.025. Zn 1-x Ga 2 O 4 :Dy x and Ga 2(1-x) O 3 :Dy 2x samples were also prepared for comparison for a dopant concentration of x = 0.02. Only the intrinsic self-activated emission of the ZnGa 2 O 4 host is observed in the photoluminescence emission spectra of Zn 0.98 Ga 2 O 4 :Dy 0.02, while both the host emission band and characteristic emission lines ( 4 F 9/2 → 6 H J ) of Dy 3+ are observed for ZnGa 2(1-x) O 4 :Dy 2x and Ga 1.98 O 3 :Dy 0.04 phosphors. The luminescent intensity differs in the phosphors due to the different energy-transfer rates from the respective hosts to the luminescent centers. Photoluminescent studies reveal the fact that Dy 3+ ions replace Ga 3+ ions in the host lattice at their octahedral sites. The source of white luminescence in the doped samples is the nonradiative resonant energy transfer via exchange interaction between the host and the activator. The CIE coordinates of the 2.5 atom % Dy 3+ -doped sample (0.32, 0.33) matches well with achromatic white (0.33, 0.33) on the chromaticity diagram.

Effect of substrate roughness on photoluminescence spectra of silicon nanocrystals grown by off axis pulsed laser deposition

Silicon nanoparticles were prepared by off axis pulsed laser deposition (PLD) technique. The optical properties of Si nanoparticles grown on quartz substrate have been characterized by optical absorption, photoluminescence, Raman, and transmission electron microscopy. TEM has demonstrated that the radius of nanocrystals decreases from 4to0.8nm as the off axis target to substrate distance increases. A blueshift up to 4.2eV is observed in the optical absorption spectra of the Si quantum dots. The slope of log(hν) vs log(α) graph shows that the optical transitions in Si quantum dots are allowed direct, allowed indirect, and direct forbidden transitions which depend on the nature of the substrate used for the growth of silicon. Relaxation of k selection rule is observed in these samples. Photoluminescence (PL) emission consists of an intense broad emission extending over visible to ultraviolet region. The photoluminescence peak energy and intensity are found to be sensitive to the nature of substrate. Possibl...

DIELECTRIC AND OPTICAL PROPERTIES OF EUROPIUM OXIDE FILMS

The dielectric properties of vacuum-deposited europium oxide films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300–543 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 A. Films deposited at higher substrate temperatures (above 423 K) exhibit improved dielectric properties owing to the recovery of stoichiometry. The frequency variation of the loss factor exhibits a minimum which increases with rise in temperature. The breakdown field strength (about 106V cm-1) is found to be thickness dependent and it varies in accordance with the Forlani-Minnaja relation. The films exhibit ohmic conduction with an activation energy of 0.86 eV at low electric fields but at higher fields the conductivity becomes space charge limited. X-ray studies show that the films are amorphous in nature. The a.c. conductivity is proportional to ω at low frequency, whereas a square law dependence is observed at higher frequencies. The optical constants n, α and k and optical band gap are calculated from the UV-visible-near-IR spectra.