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Layer-exchange crystallization for low-temperature (∼450 °C) formation of n-type tensile-strained Ge on insulator

Layer-exchange crystallization of Ge using a group-V element has been investigated to develop a low-temperature (<500 °C) formation technique of n-type tensile-strained crystalline Ge on insulator. Here, the Sb of a group-V element is employed as a catalyst. Annealing (450 °C) of a-Ge (100 nm)/Sb (100 nm) bi-layer stacked structures generates layer-exchange crystallization. Namely, Ge and Sb layers exchange their positions, and Ge layers are crystallized on insulator substrates. However, Ge evaporation occurs during annealing, and a high concentration of Sb (∼20%) remains at the Ge/insulator interface. To solve these problems, the thickness reduction of Sb films and introduction of a-Ge thin under-layers are examined. By annealing (450 °C) a-Ge (100 nm)/Sb (50 nm)/a-Ge (5 nm) tri-layer structures, layer-exchange crystallization of Ge layers on insulator without Ge evaporation or Sb residue has been achieved. This enables formation of n-type tensile-strained (∼0.3%) Ge layers (free electron concentration: ∼5 × 1017 cm−3). Moreover, crystal orientation control of grown Ge films through the introduction of the diffusion barrier is examined. These results demonstrate the possibility of layer-exchange crystallization induced by a group-V element to realize functional thin-film devices for advanced electronics and photonics.