Structure and transport properties of microcrystalline SiGe films

Amorphous Si_1-xGe_x films (x=0, 0.25, 0.5, 0.75 and 1, having boron concentrations of 5·10¹⁸, 5·10¹⁹ and 5·10²⁰ cm^-3), were deposited at low temperature by molecular beam processing on SiO ₂/Si(001) substrates. Samples were studied by in-situ TEM and in-situ XRD to follow the crystallization process. In addition, transport properties were studied in samples which were annealed in vacuum by a hot-wall furnace at temperatures between 500 and 900°C for 1 hour. The microstructure of B-doped SiGe films is characterized by a relatively large grain size (about 1 μm). The Si_0.5Ge _0.5 films have a rather high and temperature-independent Hall mobility (25 to 60 cm²/Vsec), Seebeck coefficient (~150 to 250 μV/K at room temperature) and conductivity (200 to 2000 (Ohm cm) ^-1 at room temperature). Therefore, the highly-doped μc-SiGe films that we produce in the present research project show transport characteristics comparable to the sintered SiGe materials for thermoelectric applications