Experimental and theoretical studies on self-diffusion in amorphous germanium

Self-diffusion in amorphous germanium is studied at temperatures between 325 and 370 degrees C utilizing amorphous isotopically controlled germanium multilayer structures. The isotope multilayer is epitaxially grown on a single crystalline germanium-on-insulator structure by means of molecular beam epitaxy and subsequently amorphized by self-ion implantation. After heat treatment, the diffusional broadening of the isotope structure is measured with time-of-flight secondary ion mass spectrometry. The temperature dependence of self-diffusion is accurately described by the Arrhenius equation with the activation enthalpy Q = (2.21 +/- 0.12) eV and pre-exponential factor D-0 = (2.32(-2.10)(+20.79)) cm(2) s(-1). The activation enthalpy equals the activation enthalpy of solid phase epitaxial recrystallization (SPER). This agreement suggests that self-diffusion in amorphous germanium is similar to SPER, also mainly mediated by local bond rearrangements. Classical molecular dynamics simulations with a modified Stillinger-Weber-type interatomic potential yield results that are consistent with the experimental data and support the proposed atomic mechanism.