Thermodynamic and Kinetic Properties of Amorphous Silicon Formed By Ion Implantation.

The use of ion implantation to form amorphous Si layers will be reviewed. The unique features of implantation in terms of cleanliness and controllability have allowed us to explore some of the kinetic and thermodynamic properties of amorphous Si. Solid phase epitaxy has been observed over the temperature range 500-1200C with a single activation energy of 2.7 eV. Recent measurements of ion-beam-induced crystallization and impurity segregation will be discussed. Diffusion of impurities in amorphous Si shows some similarities with diffusion in crystalline Si. The enthalpy of crystallization has been measured by calorimetry techniques to be 11.9 kJ/mole. There is little evidence of relaxation phenomena in either the diffusion or heat release measurements. We have established that amorphous Si undergoes a first order melting transition at a temperature some 250C beneath the crystal melting temperature.