  The kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) is
stud- ied in amorphous germanium (a-Ge) layers formed by ion implantation on
<100> Ge substrates. The SPE rates were measured with a time-resolved
reflectivity (TRR) system between 300 and 540 degC and found to have an
activation energy of (2.15 +/- 0.04) eV. To interpret the TRR measurements the
refractive indices of the a-Ge layers were measured at the two wavelengths
used, 1.152 and 1.532 {\mu}m. For the first time, SPE rate measurements on
thick a-Ge layers (>3 {\mu}m) have also been performed to distinguish between
bulk and near-surface SPE growth rate behavior. Possible effects of explosive
crystallization on thick a-Ge layers are considered. When H is present in a-Ge
it is found to have a considerably greater retarding affect on the SPE rate
than for similar concentrations in a-Si layers. Hydrogen is found to reduce the
pre-exponential SPE velocity factor but not the activation energy of SPE.
However, the extent of H indiffusion into a-Ge surface layers during SPE is
about one order of magnitude less that that observed for a-Si layers. This is
thought to be due to the lack of a stable surface oxide on a-Ge. Dopant
enhanced kinetics were measured in a-Ge layers containing uniform concentration
profiles of implanted As or Al spanning the concentration regime 1-10 x1019
/cm-3. Dopant compensation effects are also observed in a-Ge layers containing
equal concentrations of As and Al, where the SPE rate is similar to the
intrinsic rate. Various SPE models are considered in light of these data.
