Charge-transport properties of dendritic germanium thin films

The charge transport properties of dendritic Ge thin films on glass substrates before and after postannealing have been studied by the methods of temperature-dependent electrical conductivity measurements and temperature-dependent Hall mobility measurements. Results showed that the dendritic structure is consistent with a crystalline matrix consisting of a high density of structural defects that cause degenerate conduction at high temperatures. Postannealing of the as-prepared samples at a temperature {}570 ^∘{}C for 2 h succeeded in converting the degenerate conduction into a nondegenerate one. All the samples were found to be p-type in the low-temperature regime (20--100 K). The origin of the acceptorlike states within the forbidden gap was suggested to arise from dangling-bond-related defects, which could be partially removed by the prolonged annealing. Hall mobility (μH) data in the temperature range from 20 to 300 K revealed that the charge carriers were subjected to two kinds of scattering mechanisms. At low temperatures, ionized center scattering was found to dominate and μH showed a T^α dependence, where {α} is a positive constant; while at higher temperatures μH was found to vary as T^-0.5 rather than the expected T^-3/2 dependence. This was explained in terms of a structural-imperfection-limited mean free path of the charge carriers.