1/f noise in polycrystalline SiGe analyzed in terms of mobility fluctuations

Polycrystalline layers of Si0.7Ge0.3 were deposited using low pressure chem ical vapor deposition to a thickness of 500 nm on a n-type silicon wafer co vered by SiO2. The Si0.7Ge0.3 layers were doped with different concentratio ns of boron by ion implantation. The morphology and electrical properties h ave been characterized using atomic force microscopy, transmission electron microscopy and Hall effect. Conductance fluctuations were measured at room temperature. Decreasing boundary scattering at higher free carrier density results in increased mobility. However, surprisingly enough, we found that the lif noise parameter alpha decreases with increasing mobility, which do es not agree with the parameter alpha measured in crystalline semiconductor material grown by molecular beam epitaxy. The interpretation is that the n oise is mainly generated in the depletion region of the grains, but the Hal l mobility is reduced by the scattering at grain-boundaries, In this paper we present a detailed analysis to distinguish between 1/f noise from grain- boundaries, depletion region and neutral region of the grains. The 1/f nois e in polycrystalline SiGe can well be analyzed in terms of mobility fluctua tions in lattice scattering. (C) 1999 Elsevier Science Ltd. All rights rese rved.