Optical band gap modification and photodetector properties of au NPs doped CuZnS thin films

Abstract EN

Au nanoparticles doped CuZnS (CZS) thin films were deposited by spray pyrolysis method (SPD) onto glass and silicon substrates at temperature of 330 ºC and annealed at 450ºC.

Cu:Zn:S content was 1:1:2 and Au NPs dopant ratio was 4%, 6% and 8%.

The structural, surface morphology, optical and photodetector properties were investigated with respect to the dopant concentration.

X–Ray diffraction patterns indicate that the films have low crystallinity and polycrystalline structure nature with ZnS sphalerite cubic phase.

The intensity of diffraction peaks and the crystallite size increased with the increase of Au Np's dopant ratio.

The SEM images show a homogeneous and smooth uniform surface.

Also AFM images reveals that the roughness increased from1.95 nm for CZS (1:1:2) to 2.64 nm for CZS:Au (4%), 4.86 nm for CZS:Au (6%) and 3.82 nm for CZS:Au (8%) thin films, these increases could be probably due to the increasing concentration of atomic gold in the CZS thin films, The average grain diameter was evaluated from the plane view images for 68.99 CZS 1:1:2 and CZS:Au NPs was (93.59–102.07 nm).

Au Np's dopant ratio, the lower band gap corresponds to CuxS phase and double band gap confirms the alloy nature of material.

The decreased in energy band gap after increasing of Au Np's dopant ratio can be attributed to the red shift of the absorption edge and to the improvement in the crystallinity, increase of Au Np's ratio leads to decrease band gap from 2.5 eV to 2.39 eV.

Photodetectors CuZnS: Au Np's/Si were synthesized and I–V characteristics have been investigated, the results showed that the photocurrent increased from 0.0 to (8.65×10-7 A, 5.62×10-6 A and 5.03 ×10-6 A) at the bias voltage range of 0– 2V under illumination, and from 0.0 to (3.49 ×10-7 A, 1.9 ×10-6 A and 3.14 ×10-6A) in the dark for CZS:Au NPs (4%, 6% and 8%) ratio, respectively.

Under applied voltage of 2V, the response time was (0.8, 0.5 and 1.5 sec) respectively; whereas the recovery time was (0.6, 0.9 and 1.35 sec) and the sensitivity increased from 42.86% to 122.73%.