Disordering process of GeSb₂Te₄ induced by ion irradiation

The disordering process in crystalline GeSb₂Te₄ films has been studied by means of ion irradiation with 150 keV Ar⁺ ions. The effect of the interfaces and the role of the crystal microstructure has been investigated. The disordering path observed in a randomly oriented polycrystalline material with trigonal structure involves the transition to the disordered rocksalt structure (at fluence 7  ×  10¹³ cm⁻²) and then to the amorphous phase (at 1.5  ×  10¹⁴ cm⁻²). In GeSb₂Te₄ epitaxially grown on Si(1 1 1) the formation of the disordered rocksalt phase (DRS) occurs at much higher fluence (3  ×  10¹⁴ cm⁻²) and it is preceded by the conversion of the stable phase into the ordered rocksalt structure (at 5  ×  10¹³ cm⁻²), with the formation of ordered vacancy layers, associated to a local variation of the stoichiometry. Even by increasing the fluence up to 3.5  ×  10¹⁴ cm⁻², the films remains mainly crystalline.

The observed behaviour has been attributed to the effect of the interfaces and suggests the possibility to promote switching between the crystalline phases by interface engineering. (paper)