Amorphous Si — the role of MeV implantation in elucidating defect and thermodynamic properties

Abstract

The role of MeV implantation in producing thick amorphous Si layers has been central in elucidating several of its properties. The recent use of MeV Si beams to produce very pure layers will be reviewed. The kinetics of solid-phase epitaxy have been measured for amorphous Si layers up to 5 μm thick and the activation energy found to be 2.70 ± 0.02 eV. Calorimetry measurements of such thick layers show an interfacial heat release due to crystallization of 13.4 ± 0.7 kJ/mol and a homogeneous heat release of 5.1 ± 1.2 kJ/mol. This homogeneous heat release, associated with relaxation, is due to the annihilation of defects in the amorphous structure. These defects have been studied by ion-bombarding 500°C annealed amorphous and single-crystal Si. The formation and annihilation properties of the defects in these two states are intriguingly similar. Defects saturate in previously annealed a-Si at ion doses ~ 0.02 dpa. The presence of the defects is also manifested in measurements of the density of amorphous Si which is (1.8 ± 0.1)% less dense than the crystal. The diffusion and solubilty of Cu, Zn, Pd, Ag, Pt and Au have been measured in amorphous Si and found to be very sensitive to defect population. The various experiments show that the intrinsic defect level in amorphous Si is 1–2 at.%