nan Dhananjay

Low threshold voltage ZnO thin film transistor with a Zn0.7Mg0.3O gate dielectric for transparent electronics

A highly transparent all ZnO thin film transistor (ZnO-TFT) with a transmittance of above 80% in the visible part of the spectrum, was fabricated by direct current magnetron sputtering, with a bottom gate configuration. The ZnO-TFT with undoped ZnO channel layers deposited on 300 nm Zn0.7Mg0.3O gate dielectric layers attains an on/off ratio of 104 and mobility of 20 cm2∕V s. The capacitance-voltage (C−V) characteristics of the ZnO-TFT exhibited a transition from depletion to accumulation with a small hysteresis indicating the presence of oxide traps. The trap density was also computed from the Levinson’s plot. The use of Zn0.7Mg0.3O as a dielectric layer adds additional dimension to its applications. The room temperature processing of the device depicts the possibility of the use of flexible substrates such as polymer substrates. The results provide the realization of transparent electronics for next-generation optoelectronics.

Effect of Li substitution on dielectric and ferroelectric properties of ZnO thin films grown by pulsed-laser ablation

Li-doped ZnO thin films (Zn1−xLixO, x=0.05–0.15) were grown by pulsed-laser ablation technique. Highly c-axis-oriented films were obtained at a growth temperature of 500 °C. Ferroelectricity in Zn1−xLixO was found from the temperature-dependent dielectric constant and from the polarization hysteresis loop. The transition temperature (Tc) varied from 290 to 330 K as the Li concentration increased from 0.05 to 0.15. It was found that the maximum value of the dielectric constant at Tc is a function of Li concentration. A symmetric increase in memory window with the applied gate voltage is observed for the ferroelectric thin films on a p-type Si substrate. A ferroelectric P-E hysteresis loop was observed for all the compositions. The spontaneous polarization (Ps) and coercive field (Ec) of 0.6μC∕cm2 and 45kV∕cm were obtained for Zn0.85Li0.15O thin films. These observations reveal that partial replacement of host Zn by Li ions induces a ferroelectric phase in the wurtzite-ZnO semiconductor. The dc transport st...

Off-centered polarization and ferroelectric phase transition in Li-doped ZnO thin films grown by pulsed-laser ablation

Li-doped ZnO (Zn1−xLixO, x=0.15) thin films have been grown on platinum-coated silicon substrates via pulsed-laser ablation. The films were grown at fixed substrate temperature of 500 °C and different partial pressure of oxygen (PO2∼100–300 mTorr). The films showed (002) preferred orientation. The doping concentration and built-in potential were estimated from the capacitance-voltage characteristics. In order to investigate the phase transition behavior of the films, dc conductivity and dielectric measurements were conducted. The phase transition temperature was found to be 330 K. The activation energy (dc) has been found to be 0.05 and 0.28 eV in ferroelectric and paraelectric phases, respectively. The Zn0.85Li015O thin films exhibited well-defined polarization hysteresis loop, with a remanent polarization of 0.2 μC∕cm2 and coercive field of 25 kV/cm, at room temperature. The conduction mechanism of the laser ablated Zn0.85Li015O films was analyzed in the light of impedance spectroscopy.

Structural and optical properties of CuIn1-xAlxSe2 thin films prepared by four-source elemental evaporation

CuIn1 2 xAlxSe2 (CIASe) thin films with x ¼ 0:25; 0.5 and 0.65 were prepared by four-source elemental evaporation. The structural and optical properties were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive analysis, and optical transmission. The results showed that these films contain chalcopyrite structure with preferred orientation along (112) direction. The morphology, grain distribution and composition of CIASe films were studied and compared for different Al content. The optical studies revealed that the films were highly absorbing and the energy band gap calculated from transmission spectra for x ¼ 0:25; 0.5 and 0.65 were 1.2, 1.51 and 1.73 eV, respectively. The variation of Al content in the CIASe composition offered a very effective change in the optical band gap.

Investigations on multimagnetron sputtered Zn1−xMgxO thin films through metal-ferroelectric-semiconductor configuration

The effect of Mg doping in ZnO is investigated through structural, electrical, and optical properties. Zn1−xMgxO (0<×<0.3) thin films were deposited on Si (100) and corning glass substrates using multimagnetron sputtering. Investigations on the structural properties of the films revealed that the increase in Mg concentration resulted in phase evolution from hexagonal to cubic phase. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110 °C. The Zn0.7Mg0.3O thin films exhibited a well-defined polarization hysteresis loop with a remnant polarization of 0.2 μC/cm2 and coercive field of 8 kV/cm at room temperature. An increase in the band gap with an increase in Mg content was observed in the range of 3.3–3.8 eV for x=0–0.3. The average transmittance of the films was higher than 90% in the wavelength region λ=400–900 nm.