Mobility Behavior of Ge1-xSnx Layers Grown on Silicon-on-Insulator Substrates

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We have investigated the behaviors of the carrier mobility and concentration of the undoped Ge1-xSnx layers epitaxially grown on silicon-on-insulator (SOI) substrates. Hall measurement revealed the conduction of holes excited from acceptor levels related to vacancy defects whose concentration was as high as $10^{18}$ cm-3 in Ge1-xSnx layers. The temperature dependences of the carrier mobility and concentration in the valence band was estimated by reducing the parallel conduction component in the impurity band. The incorporation of Sn at a content lower than 4.0% hardly degraded the hole mobility of heteroepitaxial Ge1-xSnx layers. In contrast, the mobility of the Ge1-xSnx layers was improved by reducing the carrier concentration of the Ge1-xSnx layers by Sn incorporation compared with that of the Ge layer formed under the same growth and annealing conditions. This result suggests that the incorporation of Sn into Ge leads to reducing the hole concentration of the electrically active vacancy defects due to the formation of Sn-vacancy pairs.
2010-04-25