Germanium telluride

Germanium telluride (GeTe) is a chemical compound of germanium and tellurium and is a component of chalcogenide glasses. It shows semimetallic conduction and ferroelectric behaviour. Germanium telluride exists in three major crystalline forms, room temperature α (rhombohedral) and γ (orthorhombic) structures and high temperature β (cubic, rocksalt type) phase; α phase being most phase for pure GeTe below the ferroelectric Curie temperature of approximately 670 K.

Doped germanium telluride is a low temperature superconductor.

Solid GeTe can transform between amorphous and crystalline states. The crystalline state has a low resistivity (semiconducting at room temperature) and the amorphous state has a high resistivity. The drastic changes in the properties of the material have been exploited in data storage applications. The phase transitions of GeTe can be fast, reversible and repeatable, with drastic property changes, making GeTe a promising candidate in applications like radio frequency (RF) switching and direct current (DC) switching.

The synthesis described above has not reached the sized required to exhibit quantum size effect. Nanostructures that reach the quantum regime exhibit a different set of phenomena unseen at a larger scale, for example, spontaneous polar ordering and the splitting of diffraction spots. The synthesis of GeTe nanocrystals of average size of 8, 17, and 100 nm involves divalent Ge(II) chloride – 1,4 dioxane complex and bis[bis(trimethylsilyl)amino]Ge (II) and trioctylphosphine tellurium in a solvent such as 1,2 dichlorobenzene or phenyl ether. Ge(II) reduction kinetics has been thought to determine the GeTe formation. Large the Ge(II) reduction rate may lead to the increase in particle nucleation rate, resulting in the reduction of particle diameter.

GeTe has been heavily used in non volatile optical data storage such as CDs, DVDs, and Blu ray and may replace dynamic and flash random access memories. In 1987, Yamada et al. explored the phase changing properties of GeTe and Sb2Te3 for optical storage. The short crystallization time, cyclability and high optical contrast made these material better options than Te81Ge15Sb2S2 which has a slow transition time.

The high contrast in resistivity between the amorphous and crystalline states and the ability to reverse the transition repeatedly make GeTe a good candidate for RF switching. RF requires a thin layer of GeTe film to be deposited on the surface of the substrate. Seed layer structure, precursor composition, deposition temperature, pressure, gas flow rates, precursor bubbling temperatures and the substrates all play a role in the film properties.