Thermally induced irreversibility in the conductivity of germanium nitride and oxynitride films.

We report the evidence for irreversible changes in the conductivity, σ ( T ) , of a-Ge 3 N x ( 3.7 < x < 4.6 ) and quasi-stoichiometric a-Ge 2 O y N x thin films occurring at T ≳ 630 K , under high vacuum conditions. We have found that σ ( T ) curves not only depend on the material properties but also on the thermal history undertaken by films. The irreversibility in σ ( T ) , during heating in vacuum, is correlated to the transformation of the native GeO 2 into volatile GeO. Thermal annealing in N 2 atmosphere, on the contrary, results to extend film stability up to 973 K. At higher T , domes and pits are formed onto the film surface, due to the strong effusion of N-rich volatile species. Unstable N-Ge bonds can explain both the nitrogen thermodynamic instability and the Ge nano-crystallisation process occurring in a-Ge 3 N x films, upon heating until 1023 K. Compared to a-Ge 3 N x , quasi-stoichiometric a-Ge 2 O y N x is both more insulating and more stable upon heating up to 1023 K under N 2 flow, that makes it a suitable passivating layer material for the fabrication of electronic devices. [ABSTRACT FROM AUTHOR]