L. Balakrishnan

Influence of oxygen partial pressure on ferromagnetic switching characteristics of ZnO:Cr heteroepitaxial films

The effect of oxygen partial pressure on Zn0.9Cr0.1O heteroepitaxial thin films grown by radio frequency sputtering has been investigated. The grown films on Si (100) substrates have been characterised by X-ray diffractometer (XRD), photoluminescence (PL), Hall effect measurements and vibrating sample magnetometer (VSM). The XRD pattern shows that the films are preferentially oriented along (002) diffraction plane. The Hall measurement shows that electron concentration of the films decreases with increase of oxygen partial pressure. The decrease in intensity of violet band emission and red shift in near-band-edge emission observed from room temperature PL measurement have been well consistent with our electrical measurements. The room temperature VSM measurements showed that the magnetic property of ZnO:Cr film have strong dependence on oxygen partial pressures and the film grown at low oxygen partial pressure exhibits better ferromagnetism.

Fabrication of p-ZnO:ZrN thin films by RF magnetron sputtering

An attempt has been made to fabricate p-ZnO thin films from the ZrN mixed ZnO targets by RF magnetron sputtering. The targets of different ZrN concentrations (0, 1, 2, and 4 mol%) have been prepared by solid-state reaction route. The ZrN-codoped ZnO films grown on semi-insulating Si (100) substrates have been characterized by X-ray diffraction (XRD), photoluminescence (PL), Hall effect measurement, time-of-flight secondary ion mass spectrometer (ToF-SIMS), and atomic force microscopy (AFM). XRD studies reveal that all films are oriented along (002) plane. The Hall measurements showed p-conductivity for 1 and 2 mol% ZrN-codoped ZnO films. Further, it has been found that 1 mol% ZrN-codoped film has low resistivity (7.5 × 10−2 Ω cm) and considerable hole concentration (8.2 × 1018 cm−3) by optimum incorporation of nitrogen due to best codoping. The red shift in near-band-edge emission observed from PL well acknowledged the p-conduction in 1 and 2 mol% ZrN-codoped ZnO film. The incorporation of N and Zr atoms in the ZnO matrix has been confirmed by ToF-SIMS analysis. The increase in peak to valley roughness (R pv) with increase of doping concentration has been observed from AFM analysis. ZnO homojunction has also been fabricated with the best codoped p-ZnO film and it showed typical rectification behavior of a diode. The junction parameters have also been determined for the fabricated homojunction.

Realization of low resistive p-ZnO thin film by Al-As codoping

Al-As codoping into ZnO has been proposed to realize low resistive and stable p-ZnO thin film by RF magnetron sputtering. Al-As codoping has been achieved by As back diffusion from GaAs substrate and sputtering Al doped ZnO target. Hall measurements showed that the hole concentration increases with the increase of Al concentration from 1015 to 1020 cm−3. Among the grown films, 1 at% Al doped ZnO: As showed low resistivity (3.5×10−2Ωcm) with high hole concentration. X-ray diffraction shows that all the films are crystallized in wurtzite structure with (002) preferential orientation. The diffusion of As atoms from the substrate and the presence of dopants in the film have been confirmed by Rutherford ford back scattering and energy dispersive spectroscopy analysis, respectively.

Optimization of Anodic Layer and Fabrication of Organic Light Emitting Diode

Ga doped ZnO (GZO) films of different concentrations (1, 2 and 4 mol%) have been deposited on glass substrates by RF magnetron sputtering. The grown layers at room temperature have been subjected to structural, optical and electrical characterization. It has been found that 2 mol% Ga doped ZnO has best structural, optical and electrical properties which has been used as anode layer for the fabrication of Organic Light Emitting Diode (OLED). The Zn0.98Ga0.02O film was then deposited at a lower working pressure of 0.015 mbar to obtain a good carrier concentration. The OLED structure has been fabricated with best GZO as anode layer, [N, N*-Diphenyl N, N*-Di-p-Tolylbenzene-1] as hole emitting layer and (Alq3) as electron transport layer. The fabricated OLED device has been subjected to current-voltage characteristics.

Realization of n-ZnO:Ga / p-ZnO:GaP homojunction by RF magnetron sputtering

ZnO based LEDs are received great attention as it has wide band gap (∼3.36 eV) and large exciton binding energy (∼60 meV) at room temperature [1]. It is known that the basic components for LEDs are high quality p-type and n-type layers. The undoped ZnO exhibits intrinsic n-type conductivity and doping with III group elements such as B, In, Al, and Ga will enhance the electrical properties. But, it is too difficult to produce high quality p-type ZnO layers due to compensation of native defects, formation of deep acceptor and low solubility of dopants.

Fabrication of ZnO homojunction by Al-As-N tridoping

In recent years, ZnO has received great attention for optoelectronic applications (UV LEDs and LDs) because of its splendor properties such as high excitonic binding energy, high optical gain, and high radiation & temperature stability. In order to develop these ZnO based optoelectronic devices, the first step is the fabrication of high quality n- and p-type ZnO thin films. It is easy to grow low resistive and stable n-ZnO films because of the presence of native donor defects (VO and Zni). But, the p-conductivity can be realized only by suppressing these defects with suitable dopants. Different doping methods such as monodoping, codoping and cluster doping have been tried to realize low resistive p-ZnO but only few of them have succeeded despite the stability of p-conduction remains to be answered [1].