Rangarajan, N. (1987) Studies on the optoelectronic characteristics of cadmium selenide. PhD thesis, Madurai-Kamaraj University.
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Cadmium selenide is an n-type direct-band gap semiconductor having an energy band gap of 1.7 eV. Its melting point is 1260°C and density is 5.8g/c.c It has two structures (1) cubic and (2) hexagonal. Its photoconductivity lies in the range from 0.4 micrometer to 1.3 micrometer with peak photosensitivity at 0.72 micrometer. It has fact response compared to cadmium sulphide. Various techniques are available for obtaining cadmium selenide layers required for preparing photoconductive cells. They include chemical vapour deposition, close-space vapour transport, chemical bath deposition, spray pyrolysis, screen-printing, electro deposition, electrophoretic deposition, anodization, chemi plating, vacuum deposition, sputtering and electron beam evaporation. Screen-printed and sintered layer possess certain advantages. They are (1) large area photoconductive cells can be easily made. (2) They exhibit ohmic dependence of photocurrent on applied voltage. (3) Impurity incorporation is very easy. (4) Good adhesion to the substrate is obtained. (5) They do not involve the use of sophisticated and expensive equipments like vacuum system, gauges and power supplies. (6) Electrical power consumption is every low. (7) Layers can be easily obtained on any substrate whether it is conducting or non-conducting and (8) this method is very cheap. The property which is of technological interest is the dark resistivity of the cadmium selenide layers. For photoconductive work, a very high dark resistivity of the order of 108 ohm-cm is required whereas for photovoltaic work a very low dark resistivity of the order of 1 ohm-cm is required. In the present investigation, high resistivity cadmium selenide layers suitable for photoconductive cells have been obtained as a result of sintering carried out in air and also by doping with suitable acceptor impurities. Without any acceptor impurity and with suitable post heat-treatment of the sintered cadmium selenide layers in high vacuum for a specified length of time the dark resistivity could be brought down considerably. Chapter I give an introduction to the photoconductivity of solids and the general mechanism of photoconductivity. It also discusses how the photoconductivity is related to the lifetime of the majority carriers, trapping centres and sensitizing centres. The work carried out on cadmium selenide so far has also been reviewed. The various experimental techniques employed in carrying out this research work have been described. Sintering conditions of the cadmium selenide layers such as time, temperature, various atmospheres such as nitrogen, vacuum etc are studied and the results are discussed. The effect of various electrical contacts on the photosensitivity of the sintered cadmium selenide layer is dealt with. Optoelectronic properties such as spectral distribution of photoconductivity, lux-ampere characteristics, rise and decay of photocurrent and the effect of temperature and high field on the photocurrent are studied. The effect of oxygen adsorption on the properties of the sintered CdSe layers is described. Photovoltaic studies were carried out by employing the CdSe sintered layers. Various types of applications of the CdSe layers are given.
| 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 07:08 |
| Last Modified: | 12 Jun 2012 07:08 |
| URI: | http://cecri.csircentral.net/id/eprint/2806 |
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