Phase transformations in ionhyphen;mixed metastable (GaSb)1minus;x(Ge2)xsemiconducting alloys

摘要

Low energy (75ndash;175 eV) Ar+ion bombardment during film deposition has been used to produce wellhyphen;mixed amorphous GaSb/Ge mixtures which, when annealed, transform first to single phase polycrystalline metastable (GaSb)1minus;x(Ge2)xalloys before eventually transforming to the equilibrium twohyphen;phase state. At 500thinsp;deg;C, for example, the annealing timetarequired for the amorphous to crystalline metastable (ACM) transformation was sim;10 min, whiletafor the crystalline metastable to equilibrium (CME) transformation was 6 h. The exothermic enthalpy of crystallization and the onset temperature of the ACM transition were determined as a function of alloy composition using differential thermal analysis. The thermodynamic data was then used to calculate the surface energy per unit area sgr; of the amorphous/metastablehyphen;crystal interface. sgr; was found to exhibit a minimum betweenx=0.3 and 0.4. The driving energy for the transition from the crystalline metastable state to the equilibrium twohyphen;phase state was of the order of 0.12 kJthinsp;cmminus;3while the activation barrier was sim;19 kJthinsp;cmminus;3. Thus, the metastable alloys, which had average grain sizes of 100ndash;200 nm and a lattice constant which varied linearly withx, exhibited good thermal and temporal stability.