Tushar Ghosh

Enhanced Photoluminescence and Photoconductivity of ZnO Nanowires with Sputtered Zn

We have sputtered Zn onto quasi-one-dimensional ZnO nanowires (NWs) in order to investigate the effect of Zn diffusion on the photoluminescence and photoconduction properties of ZnO NWs. Elemental mapping clearly indicates higher Zn concentration in the NWs due to diffusion of Zn. The Zn-sputtered NWs show an enhanced ultraviolet emission with 7 nm red shift. Since the ionization energy of Zni is 51 meV, the enhanced PL emission with a red shift is correlated to the coupling between free exciton and zinc interstitials (Zni) defects. The photocurrent transients show almost 20 times more photocurrent generation in Zn/ZnO NWs compared to the as-grown NWs. In contrast, the thin film shows no significant change in the photoluminescence and photoconductivity. Based on the photoconductivity and photoluminescence results, we predict that Zn diffusion in the NWs occurs easily compared to the films because of the smaller dimensions of the NWs.

Effect of Cu Doping in the Structural, Electrical, Optical, and Optoelectronic Properties of Sol-Gel ZnO Thin Films

The effect of Cu doping (0.08-4%) on the structural, electrical, optical, and optoelectronic properties of sol-gel ZnO thin films deposited on glass substrates have been investigated. X-ray diffraction studies show that the doped films are single-phase wurtzite structure with random orientations. A decreasing trend in the c-axis parameter up to 0.5% is observed followed by an increasing trend above that. Field-emission scanning electron microscopy shows a grain texture. The energy dispersive spectroscopy as well as the film color confirms the Cu doping. Optical transmittance measurements show 80% transparency in the visible region for the films up to 0.3% Cu content. The doped films become very resistive as indicated by the four probe electrical resistivity and current-voltage measurements. The photoluminescence spectra reveal with Cu doping, a green emission at 515 nm appeared and the UV peak intensity at 376 nm is drastically lowered. However, no green emission is observed as the doping is increased beyond 0.5%. The changes in the structural, electrical, and optical properties are correlated to interstitials defects. The photoconductivity studies show that the UV sensitivity of the films is enhanced up to 0.1%, which indicates that the films can be used as UV sensors.

Highly enhanced ultraviolet photoresponse property in Cu-doped and Cu?Li co-doped ZnO films

A highly enhanced ultraviolet (UV) photodetection property has been achieved in 0.1% Cu doped and 0.1% Cu–2% Li co-doped sol–gel ZnO thin films. The 0.1% Cu doped and 0.1% Cu–2% Li co-doped films show UV photosensitivity values (photo-to-dark current ratio) of around 2000 and 5000, respectively, which is one order of magnitude higher than the undoped film. The co-doped film shows a decrease in the photocurrent growth and decay time constants compared with the Cu doped one. The increased photosensitivity indicates that these low-cost doped and co-doped films are promising for UV photodetection applications.

Improved electrical transport properties in p-type ZnO film by Rapid Dark thermal annealing process

A rapid dark thermal annealing process at 800 0C of radio frequency sputtered P doped ZnO thin films have resulted in improved electrical transport properties with hole concentration of 1 × 1018 cm-3, mobility 4.37 cm2/Vs and resistivity 1.4 Ω-cm. X-ray photoelectron spectroscopy shows the presence of inactivated P in as-grown ZnO films.