We demonstrate the possibilities of plasma enhanced chemical vapor deposition (PECVD) and solid phase epitaxy to obtain germanium on silicon with excellent crystalline properties, even for very thin layers (< 100 nm). Amorphous germanium layers are deposited by PECVD on silicon substrates. Deposition of an amorphous layer, without the presence of crystalline seeds, is critical. Crystalline inclusions must be avoided to obtain high crystal quality and a smooth surface after crystallization. PECVD is well suited for deposition of amorphous layers because low temperature deposition and high growth rates are possible. Additional experiments with molecular beam epitaxy show that it is not mandatory to have hydrogen present inside the germanium layer to obtain highly crystalline germanium. Atomic hydrogen plays, however, an important role during deposition by lowering the surface adatom mobility and consequently increasing the disorder of the deposited layer. Synchrotron X-ray diffraction shows no germanium diffraction, indicating that the layer does not contain crystalline seeds. Crystallization can be performed at limited temperatures: Raman measurements show crystallization between 400 and 425 °C. Another important advantage of the proposed method is the scalability: germanium layers of larger diameter can be obtained by simply using larger silicon substrates.
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