LPE Growth of Atomically Flat Ge Layer on a Mesa Pattern

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LPE GROWTH OF ATOMICALLY FLAT Ge LAYER ON A MESA PATTERN Takahiro Maruyama1,2, Keiji Matsuda1, Norikazu Saikawa1, Shigeya Naritsuka1,2 1 Dept. of Materials Science & Engineering, Meijo University, 2 Meijo University, 21st CENTURY COE program “NANO FACTORY” 1-501 Shiogama-guchi, Tempaku-ku, Nagoya 468-8502, Japan

ABSTRACT Aiming at the growth of step free surface on mesas, we tried to suppress the formation of two-dimensional nucleation on grown surface by decreasing the supersaturation. When the supersaturation was enough small at the growth temperature below 400 ℃, flat facets were formed on some mesas after the LPE growth for 30 min. We considered that these facets are formed on mesas with dislocation-free surface, considering the dislocation density of Ge substrate. AFM observation indicated that some triangle hollows with monolayer step in depth were present on these facets, but that the region among the hollows was atomically flat. It was also found that the amount and the size of the hollows were related to the growth temperature. Our results show the possibility that atomically flat Ge area beyond 100 μm2 will be obtained by the control of the growth condition. INTRODUCTION Control of the growth face on an atomic scale is important for the fabrication of coming nano-size deveices, because atomic-scale surface steps may affect the quality of crystal grown on it. In order to obtain an atomically flat surface, it is necessary to grow an atomically flat face. This requires that two-dimensional (2D) nucleation must be prevented and that growth with step flow mode is carried out. So far, step-free surfaces on device-size have been realized for GaAs(100) [1] and SiC(0001) [2] by utilizing dislocation-free mesas. However, step-free Ge surface has never been obtained, though Ge(100) has been expected for one of candidates as an interlayer in GaAs/Si heteroepitaxy [3-5]. In our study, aiming at the growth of step free Ge surface on mesas, we tried to suppress the formation of 2D nucleation on grown surface and to carry out the step-flow growth by LPE. EXPERIMENTAL DETAILS Sb doped Ge (111) wafers with a etch pit density of about 104 cm-2 were used as substrates in our LPE growth. The density of monolayer steps was about 30 nm-1.

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By standard photolithographic technique, mesa patterns were prepared on Ge(111) substrate. They have square-shaped mesa areas with an edge length of 2-15µm separated by grooves with 8µm wide and 1µm deep. Normarski optical micrograph for one portion of mesa structure is shown in Fig. 1. After wet-etching for removal of surface oxide, they are put into the crucible of a slide boat LPE system. LPE growth was performed in pure hydrogen ambient gas. The solution used consisted of pure indium as solvent and Ge as solute. When the crucible containing the solution and the substrate was heated to the growth temperature, the solution was put onto the saturation substrate. After the solution was saturated, we moved the solution to the “empty” area where no substrate was present, and