Diffusion of boron in germanium at 800–900 °C revisited

Abstract

Diffusion of boron (B) in germanium (Ge) at temperatures ranging between 800°C and 900°C is revisited following the most recent results reported by Uppal et al. [J. Appl. Phys. 96, 1376 (2004)] that have been obtained mainly with implantation doped samples. In this work, we determined the intrinsic B diffusivity by employing epitaxially grown alternating undoped and B-doped Ge layer structures with three different dopant concentrations of 4×1017 cm−3, 1×1018 cm−3, and 3×1018 cm−3. The diffusional broadening of B was analyzed by means of secondary ion mass spectrometry (SIMS) and numerically described to determine the diffusion coefficient. Additional SIMS analyses revealed a gradient in the oxygen (O) background concentration of the epitaxially doped Ge structure. A high O content observed in near-surface regions correlates with enhanced B diffusion. In contrast, B-doped regions with low O content showed a significantly lower B diffusivity representing the intrinsic diffusivity. The B diffusion coefficients are significantly lower compared to literature data and best described by a diffusion activation enthalpy and a pre-exponential factor of (4.09±0.21) eV and 265−237+2256 cm2 s−1, respectively.