Abstract
PbS thin films are fabricated from 99.9% PbS powder on glass substrates using the vacuum evaporation method. Some of the samples are then treated in an advanced process called annealing. Samples are annealed in temperatures of 80, 100, 120 and 150°C for two h. Characterization using an X-Ray Diffractometer (XRD) resulted in values of lattice constant of the films ranging from (5.782±0,010) A to (5.919±0,006) A. These values are quite different from the standard, probably because the films are stressed and strained. The grains have sizes ranging from (266.440±0.001) A to (694.059±0.002) A, where the greatest grain size was found as deposited thin film because it was directly condensed from powder vapor during the deposition process and after they are annealed, the grain size becomes smaller. The average internal stress has values ranging from (0.36±0,006) × 109 N/m2 to (3.247±0.010) ×109 N/m2 and microstrain ranging from (2,864±0.006) × 10-3 to (25.94±0,01) ×10-3. It was found that the film which has the greatest stress and microstrain is the film with the annealing temperature of 150°C, showing that the annealing process exerts force on the film following the rising of temperature. Use of a Scanning Electron Microscope (SEM) shows the surface pictures of the deposited thin film and the film annealed at 120°C. Furthermore, the thickness of the samples is obtained by using the cross section of the films and showed that the thickness of the deposited thin film is between 0.63 and 1.30 microns and the thickness of the film annealed at 120°C is between 3.37 and 4.34 microns. The best quality thin film from this research is that annealed at 120°C, because it showed more peaks than the other samples. It can be concluded that the annealing process had effects on the structures, grain size, strain and stress of the crystals.
Highlights
Lead Sulfide (PbS) is a semi-conductor with a gap of energy and has a cubic structure, 0.41 eV
In the X-Ray Diffractometer (XRD) pattern of annealing samples, there is no peak at the angle of 2θ = 13°, this shows that the substrate peak is no longer detected by the annealing process, it is concluded that the annealing process gives effect the of loss of impurity
The samples subsequently selected to be characterized by using Scanning Electron Microscope (SEM) are as-deposited thin film samples and samples that have been annealing at 120°C, as shown, the average value of internal stress and microstrain compared to other samples as well describes the better peaks
Summary
Lead Sulfide (PbS) is a semi-conductor with a gap of energy and has a cubic structure, 0.41 eV. PbS Thin film is usually used in Infrared (IR) detectors. PbS Materials have potential applications with high-speed changes, because they have exceptional properties against thirdorder nonlinear optics. PbS is useful for making devices that require semi-conductors with small energy gaps as well as with optical absorption and emission in the red and near infrared spectrum areas (Ji et al, 2003). Various methods are used in thin film fabrication, vacuum evaporation, cathode sputtering, chemical deposition, vapor deposition, combustion and anodic oxidation (Hass and Turner, 1959). For purposes of optical coatings, the vacuum evaporation method is commonly used. Diaphragms and rotation sector wheels and the possibility to move the substrate during deposition, the film may have a uniform thickness with different distribution as desired
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