Some Aspects of Photoconductivity in Cadmium Selenide Crystals

Bube, Richard H.; Barton, L.

doi:10.1063/1.1744410

Cited by 58 publications

(21 citation statements)

References 15 publications

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“…When crystals of this same type are annealed above 500~ in vacuum, dark conductivity with an activation energy of 0.14 ev is found (17). This result indicates that the density of 0.14 ev donors is increased by the vacuum anealing to the point where the effects of oxygen adsorption can be overcome.…”

Section: Discussionmentioning

confidence: 84%

The Basic Significance of Oxygen Chemisorption on the Photoelectronic Properties of CdS and CdSe

Bube

1966

J. Electrochem. Soc.

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The long-known phenomenon of oxygen chemisorption on CdS and CdSe, more intensively studied recently, is shown to have a basic significance for the photoelectronic properties of thin crystals or layers. It is proposed that every "pure" crystal of CdS or CdSe is of relatively high conductivity [--~10 -6 (ohm cm) -1] and high photosensitivity (electron lifetime of 10 -3 sec) as prepared by standard techniques. If the crystal or layer is thin enough, oxygen adsorption obscures these properties and gives the appearance o5 a highly insulating insensitive material. Smaller effects are found in crystals containing deliberately incorporated impurities as long as the Fermi level at room temperature lies above the level associated with the surface state for chemisorbed oxygen. Because of the universal presence of oxygen chemisorption effects, every experiment in which the effect of heat, vacuum, or photoexcitation are investigated toward understanding the nature of photochemical. changes, must be interpreted in the light of the significant effects associated with the simple desorption of oxygen.The effect of oxygen on the photoelectronic properties of CdS and CdSe has been known from the early days of research in this area. A common prescription for improving the light-to-dark resistance ratio of photoconducting cells was to bake the cells in air to increase the dark resistance (1). The importance of adsorbed oxygen in determining measured values of dark resistance and photosensitivity in CdS (2, 3) and CdSe (4) was investigated a number of years ago, but it is only in recent years that the general importance of these effects has been realized. The effect of adsorbed oxygen on the photovoltaic effect of CdS has been studied by Williams (5) and by Haas, Fox, and Katz (6), on the lifetime and response time ~[or strongly absorbed light in CdS by Mark (7-9), on the conductivity of CdSe layers by Somorjai (10), on the photoelectronic properties of sintered layers of CdS-CdSe and CdSe by Shear, Hilton, and Bube (11), and on the photo-Hall effect of sintered layers by Robinson and Bube (12). The importance of oxygen chemisorption phenomena in simulating other types of photochemical changes has also been discussed for CdS-CdSe crystals (13), for which the electron lifetime at room temperature could be varied by a factor of 20 by varying the amount of adsorbed ox.-ygen.It now appears that what was originally believed to be an appreciable effect of importance for only a few specially prepared crystals or for particular excitation conditions is in fact a quite general effect that can have a profound influence on the photoelectronic properties of CdS and CdSe. The effects would be expected to be the most pronounced for thin crystals or layers of these materials for which surface chemisorption of oxygen could have electrical effects extending throughout the volume of the material.Mark has given a thorough report on the phenomenon of oxygen chemisorption on CdS crystals, both as to its kinetics and its energetics. He has worked with str...

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Section: Discussionmentioning

confidence: 84%

The Basic Significance of Oxygen Chemisorption on the Photoelectronic Properties of CdS and CdSe

Bube

1966

J. Electrochem. Soc.

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“…Their values and the activation energies associated with the peaks determined by the initial rise method 22 are given in Table V. In the literature, TSC measurements have been reported on CdSe crystals using light. Bube et al 23 reported energy levels at 0.14, 0.3, 0.5, and 0.63 eV, Kindleysides et al 24 30°C (eV) 0.67 ± 0.03 10 -7 -10 -6 10 -8 -10 -7 1.1 ± 0.1 10 -6 -10 -5 10 -7 -10 -6 1.3 ± 0.01 10 -6 -10 -5 10 -7 -10 -6 -120°C (eV) 0.67 ± 0.03 10 -7 -10 -6 10 -8 -10 -7 1.3 ± 0.01 10 -7 -10 -6 10 -8 -10 -7 Table V, apart from that at 1.1 eV.…”

Section: Tscmentioning

confidence: 98%

“…Bube et al 23 postulated that levels at about 0.1 eV and 0.6 eV were different ionization states of an anion vacancy, while Yodogawa 19 stated that they were due to selenium vacancies. As discussed in the resistivity and photocurrent spectral response sections these levels could also be due to impurities substituting on the lattice sites.…”

Section: Tscmentioning

confidence: 98%

Effect of oxygen on the properties of encapsulated polycrystalline CdSe films

Lee

Langford

Wright

et al. 2000

J. Electron. Mater.

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“…[1][2][3][4] However, little work was done on the influence of the ionizing radiations on their physical properties. A suitable band gap and optical properties recommend CdSe as a very promising material for optoelectronic applications like solar cell structures.…”

Section: Introductionmentioning

confidence: 99%