Pseudomorphic Si 1− yC y and Si 1− x− yGe xC y alloy layers on Si

Abstract

High-quality pseudomorphic Si 1− y C y and Si 1− x− y Ge x C y alloy layers with a carbon concentration up to 7% are prepared by solid-source molecular beam epitaxy. Near band-edge photoluminescence (PL) is observed from Si/Si 1− y C y multiple quantum well (MQW) structures. The bandgap in the pseudomorphic films is reduced by about 65 meV per percent C. The data from Si/Si 1− y C y MQWs indicate a type-I heterostructure with the band offset being mainly in the conduction band. In Si 1− x− y Ge x C y MQWs compressive strain caused by Ge is partially compensated by C alloying and the bandgap increases with y. PL measurements from closely spaced Si 1− y C y /Si 1− x Ge x layers show a lower transition energy than that of isolated Si 1− y C y and Si 1− x Ge x reference samples. This is attributed to spatially indirect PL transitions between the electrons confined in the Si 1− y C y layers and the heavy holes located in the Si 1− x Ge x layers. The PL is dominated by no-phonon recombination. Electrical properties of n-type doped thick Si 1− y C y layers and modulation doped p-type Si/Si 1− x− y Ge x C y quantum well structures are presented. No carrier capture by C or C-related defects is observed at room temperature. A significant mobility enhancement is measured for n-type doped strained Si 0.996C 0.004 layers at temperatures below 180 K, which is attributed to the splitting of the Δ valleys in the conduction band. In a modulation doped p-type Si 0.49Ge 0.49C 0.02 QW we observe an improved hole mobility at room temperature and 77 K compared to a corresponding sample without C, which is a consequence of the reduced strain in the layer due to substitutional C. © 1997 Elsevier Science S.A. All rights reserved.