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The electrical and optical material properties of epitaxial Ge1−xSnx and SiyGe1−x−ySnx are of high interest for novel device applications. However, the limited Sn solubility in Ge makes the epitaxial growth of Ge1−xSnx and SiyGe1−x−ySnx challenging. Most of the literature describing the epitaxial growth is for Ge2H6 and SnCl4 as Ge and Sn precursors, respectively. A more recent publication deals with the epitaxial growth of high-quality Ge1−xSnx with the more conventional GeH4. In this manuscript, we compare the structural and optical material quality of Ge1−xSnx, epitaxially grown on Ge virtual substrates as a function of growth pressure, growth temperature, the choice of the carrier gas (H2 or N2) and the choice of the Ge precursor (GeH4 versus Ge2H6). The best material quality in terms of surface morphology and photoluminescence characteristics is obtained if GeH4 is used as a Ge precursor. For Ge1−xSnx grown with Ge2H6 and at atmospheric pressure, pyramidical defects can be seen and there is a risk for uncontrolled local Sn agglomeration. The pyramidical defects are not observed on Ge1−xSnx layers grown at reduced pressure, but the highest achievable substitutional Sn concentration is lower. No pyramidical defects are found for Ge1−xSnx layers grown with GeH4 and the issue of uncontrolled local Sn agglomeration does not appear. [ABSTRACT FROM AUTHOR]

We report the metal-organic chemical vapor deposition method for epitaxy of n+-Ge and Ge1−xSnx layer with an electron concentration as high as 2 × 1019 cm−3 by in situ phosphorus (P) doping. In this study, we examined MO precursors of tertiary-butyl-germane (t-BGe), tri-butyl-vinyl-tin (TBVSn), and two kinds of P precursors of tri-ethyl-phosphine (TEP) and tertiary-butyl-phosphine (t-BP). We have investigated crystalline and electrical characteristics of P-doped Ge and Ge1−xSnx layers. In the case of using TEP, the P-doped Ge0.98Sn0.02 epitaxial layer grown at 320 °C on virtual Ge substrate was demonstrated, in which the chemical P-incorporation as high as 1 × 1019 cm−3 and the full electrical activation of P. By using t-BP instead of TEP, the chemical P-incorporation as high as 8.1 × 1019 cm−3 was achieved for Ge epitaxial layer grown at 300 °C. It is found that the activation energy of the growth rate of Ge and P with t-BGe, TEP, and t-BP was estimated to be 1.0−1.2, 2.1, and 1.1 eV, respectively. The precursor combination of t-BGe and t-BP has a wider temperature window for a lower growth temperature. In situ P-doping with t-BP enables us to grow the Ge0.975Sn0.025 epitaxial layer with an electron concentration as high as 1.7 × 1019 cm−3 at the temperature as low as 300 °C. For both cases of TEP and t-BP, we observed that increasing Sn content significantly reduces the P-incorporation, which is not common phenomenon in a conventional CVD growth. [ABSTRACT FROM AUTHOR]