Nagarajarao, K. (1987) Studies on the optoelectronic characteristics of cadmium sulphoselenide. PhD thesis, Madurai-Kamaraj University.

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Abstract

Interactions of light and electricity within matter have been known and studied for quite a long time. However, a systematic exploration of many relations among optical and electronic phenomena has a more recent history. Solid state optoelectronics is concerned with the technological exploitation of these relations. Photoconductivity studies illuminate the internal electronic processes in semiconductors and helps in the development of highly sensitive materials and devices. Photoconductivity is the increase in electrical conductivity of a material due to adsorption of radiation by it. Materials with special imperfections incorporated during preparation, give large signals. Cadmium sulphide and cadmium selenide are the II – VI compound semiconductors which are useful in the visible and near infrared range. For low levels of illumination ( <=301x), cadmium sulphide is sluggish in response (response time 100 v m.sec.) while cadmium selenide has a faster response under similar conditions (~30 m.sec.). Cadmium sulphide and cadmium selenide form a continuous series of substitution solid solutions and it is reasonable to expect some of these solid solutions might exhibit a broader spectral sensitivity coupled with faster response. Of the various methods available for the preparation of II – VI compound semiconductor layers, sintering of screen printed layers is, by far, the most flexible and inexpensive method for large scale preparation of highly sensitive layers. No systematic studies are reported on sintered cadmium sulphoselenide layers, though quite a large numbers of patents and reports on these for specific purposes are available besides some published literature. Systematic studies on the preparation of photoconductive grade CdS and CdSe powders and sensitization and sintering of these powders to obtain optimum photosensitivity stability have been made. Analyses of the powders and sintered layers by AAS, polarography and EPMA as well as X-ray characterization for true solid solution formation have been made. The effect of various electrode materials like indium, silver, graphite, cadmium oxide and copper are examined and the effect of diffusion of the corresponding ions into the photoconductive layers on the current-voltage behavior both in the dark illumination are examined in detail. The optoelectronics properties like spectral distribution of sensitivity with composition, lux-ampere characterization and response time studies have been measured and correlated. An attempt has been made for the first time in the case of sintered layers to further enhance the sensitivity CdSxSe(1-x) layers, by several methods, where such high sensitivity is called for, in specific applications. The possibility of using these CdSxSe(1-x) layers in sintered CdSxSe(1-x) : Cu2S/Cu2Se and CdSxSe(1-x) : Tl2S photovoltaic solar cells has also been examined. Photoconductive CdSxSe(1-x) cells will continue the interest of the solid state scientists and future applications may include image intensifiers and image storage panels in solar energy conversion and in electro photography. Logic flexibility can be incorporated into optoelectronic network using threshold of photosensitivity. Such devices will tend resemble more and more that of biological neural network such as neuro-retina in vertebrates, which will response only to inputs which are characteristic of some specific behavior. Intelligence coding, language transformation and automation of thought processes are some of the lines which will continue to interest the optoelectronic scientists.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	opto electronics; cadmium selenide
Subjects:	Electrochemical Materials Science
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	12 Jun 2012 07:04
Last Modified:	12 Jun 2012 07:04
URI:	http://cecri.csircentral.net/id/eprint/2805

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