Chalcogenide alloys

Investigation of Amorphous Chalcogenide Alloys Using Laser Raman Speetroscopy... 

The few surface studies reported suggest the presence of a considerable density of surface and gap states in the amorphous semiconductors studied. Kastner and Fritzsche (1970) found that one monolayer of H2O adsorbed on a 1000 A thick film of chalcogenide alloy increases its conductance by less than one percent. Amorphous Ge evaporated at room temperature is porous to H2 0 so that a large area of internal surfaces can be covered with water. A density of 5 X 10 H2 0/cm absorbed in a 1000 A thick Ge film produced an increase in conductance by only 10 percent. These small changes contrast strongly with the behavior of crystalline semiconductors. They suggest a large density of surface and gap states. 

Hall (1970) interpreted the high field data on chalcogenide alloys with this relaxation and obtained g(Ep) = 2 X lO eXT cm" for low fields and 6 X 10 eV cm for high fields. Koc, Zavetova and Zemek (1972) obtained g(Ep) = 1.5 X lO eV cm" for a-Ge in the same manner. An exponential field dependence of the conductance is often observed. But it can also arise from a decrease of the thermal activation energy AE by a uniform field in the bulk as discussed in the next section. The crucial test for SCLC, the dependence of j and on the electrode separation L has not been performed. 

This review confines itself to the discussion of switching and memory devices made of chalcogenide alloy glasses because these devices are much further developed than the oxide devices and have been studied more intensively in recent years. 

An extensive study of the stability and the extent of glass forming regions in chalcogenide alloys has been performed by Hilton, Jones, and Brau (1964, 1966a, 1966b), Hilton (1970), Haisty and Krebs (1969a, b), and de Neuf ville (1972). 

Chalcogenide alloys such as GeSbTe-based compounds are of interest for applications in rewritable optical media (Digital Versatile Disc, Blu-ray disc) and in non-volatile electronic memory devices [1-5]. Both applications rest on a fast and reversible transformation between the crystalline and amorphous phases which represent the two states of the memory. The phase change is induced by heating, either... 

Phase change materials based on chalcogenide alloys are of widespread use in rewritable optical media (Digital Versatile Disc, Blu-ray disc) because of the strong optical contrast between the amorphous and crystalline phase (see inset of Fig. 15.9). Such a strong optical contrast is rather unusual since in typical semiconductors (e.g. GaAs in [91]) the amorphous and the crystalline phases have a similar... 

Phillips J. C., Topology of covalent non-crystalline solids II Medium-range order in chalcogenide alloys and Si(Ge), J, Non-Cryst. Solids, 43, 37-77 (1981). 

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