Fast epitaxy of Ge on Si(001) was realized by DC sputtering at 2.1 nm · s −1 and 360 • C; the resulting film was optically flat without a cross-hatch structure. After annealing at 700 • C, 90 • -full-edge dislocations dominated the Ge-Si interface and the threadingdislocation density (TDD) of the Ge film was below 10 4 cm −2 , which is three orders of magnitude lower than the value of Ge films prepared by other methods. The extremely low TDD might be attributable to the spaces vacated by desorbed Ar within the film that served as dislocation sinks during sputtering. Acceptor-band conduction, which was at 0.02 eV above the valence band and was induced by dislocations, was observed with a hole mobility of 3-10 cm 2 · V −1 · s −1 in the film prepared without annealing. After annealing at 700 • C, the ionized-defect scattering in the film was considerably decreased and a mobility of 1180 cm 2 · V −1 · s −1 was obtained. The direct band gap energy of the film prepared without annealing was 0.81 eV, and became 0.79 eV after annealing.

Direct-current sputter epitaxy of Si on a Si(001) substrate was realized at 175 °C at a growth rate of 3.3 nm·s−1 and was applied to form n+-emitters of crystalline-Si solar cells. A solar cell with a 50-nm-thick n+-emitter exhibited a short current density of 23.8 mA·cm−2 owing to an increased internal quantum efficiency at wavelengths between 400 and 600 nm. The improved efficiency was due to the step junction characteristics of the epitaxially grown n+-emitter exhibiting a better response at short wavelengths, a performance better than that of the graded junction formed by thermal diffusion.

Heavily doped p + or n + Ge films were grown on Si substrates by sputter epitaxy. Ge was cosputtered with Al or Sb to add dopant impurities. The maximum carrier densities were 1.0 ' 10 21 for p-type films and 8.4 ' 10 19 cm %3 for n-type films. The activation ratio of Sb was 56%. A pn junction diode was fabricated on a Si(100) substrate; it exhibited a good rectifying property with an on/off ratio of 529.

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