Semiconductor surface diffusion: Nonthermal effects of photon illumination

Nonthermal influences of photon illumination on surface diffusion at high t emperatures have been measured experimentally. Activation energies and pre- exponential factors for diffusion of germanium, indium, and antimony on sil icon change by up to 0.3 eV and two orders of magnitude, respectively, in r esponse to illumination by photons having energies greater than the substra te band gap. The parameters decrease for n-type material and increase for p -type material. Aided by results from photoreflectance spectroscopy, we sug gest that motion of the surface quasi-Fermi-level for minority carriers acc ounts for much of the effect by changing the charge slates of surface vacan cies. An additional adatom-vacancy complexation mechanism appears to operat e on p-type substrates. The results have significant implications for aspec ts of microelectronics fabrication by rapid thermal processing that are gov erned by surface mobility.