The concentration profiles of B which had been diffused, from polycrystalline material, into underlying monocrystalline material were analyzed by means of secondary ion mass spectrometry. The co-diffusion of As and B was studied in an emitter and extrinsic base configuration. The process was investigated by carrying out simulations. These indicated that diffusion of the dopant at the lowest fluence was slowed much more by the in-depth inhomogeneous grain growth that was induced by amorphization and annealing, than by a built-in electric field. It was assumed that the dopant, at the highest doses, saturated the grain boundary traps. This was true of B. In a first poly-Si layer, the diffusivity (table 25) could be described by:

D (cm2/s) = 0.019 exp[-2.5(eV)/kT]

In a second poly-Si layer, the diffusivity could be described by:

D (cm2/s) = 0.000032 exp[-1.86(eV)/kT]

A.Merabet, C.Gontrand: Physica Status Solidi A, 1994, 145[1], 77-88

Table 25

Diffusivity of B in Poly-Si Layers