THE STUDY OF STRUCTURAL AND ELECTRICAL PROPERTIES OF LEAD SULPHIDE (PbS) THIN FILM DEPOSITED THROUGH CHEMICAL BATH DEPOSITION
1.1 Background of the Study
In view of the rapid depletion of existing conventional energy resources, due to the high rate of consumption the world over, it’s obvious that mankind is heading towards an energy crisis. Today energy consumption per capita is synonymous with the standard of living of a nation and raise world population, standard of living of developed and developing nation and the trend towards higher technologies on the increases. It is evident that our oil wells, the source of the world well-known major energy resources petroleum will sooner or later dry up. To avert this impending energy crisis and further meet up with energy needs of nations, renewable energy technological revolution is the only answer (Cosmas, 1989).
Renewable energy source that can be developed include non-exhaustible energy source such as sunlight, ocean currents, waves, falling water, wind natural energy stocks whose replenishment is far greater than projected human use. Of this wide range of energy choice, sunlight, or solar energy is certainly one of the most attractive. Since the solar energy is more abundant in the poorer and less developed countries of the world, it is hoped that if this particular source of energy is researched into a developed the bridging of the technological gap between the third world countries and most of the developing countries is then feasible.
Semiconductor materials are always the focus in material science due to their outstanding electronic and structural properties and have potential application in various devices such as light emitting diodes, single electron transistors, and field effect thin film transistors. In principle, the electronic and structural properties of semiconductor materials are tunable by varying their shapes and sizes. So it is one of the desired goals in material science to have precise control of the morphology of semiconductor materials. As an important IV-VI group semiconductor, Lead sulfide (PbS) has attracted considerable attention due to its small direct band-gap (0.41eV at 300K) and a large excitation Bohr radius of 18nm. Lead sulfide (PbS) is an important direct narrow gap semiconductor material with a band gap of 0.4eV and has a cubic structure. Due to their suitable band gaps, PbS thin films are extensively used in IR detectors. Thin film of lead sulfide was establish to have very significant application in the manufacture of photoconductive infrared detectors, transistors, contact rectifiers, prisons, lenses, windows and other components of optical system. This material has also been used in many fields such as humidity, photography, solar absorption photo-resistance, diode lasers, and temperature sensors, decorative and solar control coatings.
The chemical bath deposition (CBD) method is attracting considerable attention, as it does not require sophisticated instrumentation. It is relatively cheap, simple to handle, convenient for large area deposition and capable of yielding good quality thin films (Uhuegbu, 2011)
Thin films of PbS have been prepared with various physical and chemical thin film deposition techniques, such as chemical bath deposition (CBD), electro-deposition (ED), chemical spray deposition (CSP), successive Ionic layer adsorption and reaction (SILAR), electrochemical atomic layer epitaxy (EC-ALE), atomic layer decomposition (ALD) and thermal evaporation technique. Among these different techniques, bath technique is advantageous on account of suitable method in the country. It also allow a uniform wide area deposition (Ahuome and Onimsi, 2016). As earlier mentioned, the availability of raw materials is an important factor in fabricating solar cells for solar energy conversion. Thin film devices will typically be about 5µm to 50µm thick, in contrast to bulk devices which are about 150µm to 250µm thick, it shall be pointed out.