Epitaxy of Pseudomorphic GeSn Layers with Germane (GeH4) or Digermane (Ge2H6) as Ge Precursors and Tin Tetrachloride (SnCl4) as the Sn Precursor

We have benchmarked germane and digermane for the growth of pseudomorphic GeSn layers on Ge Strain-relaxed Buffers, themselves on Si(001) substrates. For a fixed GeH4 partial pressure (1.28 Torr), the GeSn Growth Rate (GR) increased linearly with the SnCl4 flow at 349°C. That increase was sub-linear at 325°C. The Sn content was almost steady with the SnCl4 flow at 349°C. Meanwhile, it increased then decreased at 325°C. We otherwise had exponential increases, over the 301°C - 349°C range, of the GeSn GR with the temperature, with similar activation energies around 10 kcal mol.-1 for both chemistries. In contrast, the Sn content linearly decreased as the temperature increased, with a slope which was less for GeH4 than for Ge2H6 (- 1.0% / 10°C instead of - 1.7% / 10°C). Although the GeH4 flow was 4 times the Ge2H6 one and the chamber pressure 4 times higher (400 Torr versus 100 Torr), GeSn GR were almost the same for a given SnCl4 flow. Sn contents were by contrast significantly lower with GeH4 than with Ge2H6. Halving, for the same GeH4 flow, the SnCl4 flow resulted in GeSn GR 40% lower but slighly higher Sn contents, which was once again counterintuitive. GeSn layers were flat and of high crystalline quality with both chemistries. Finally, while the GeSn GR and Sn contents were rather uniform over the 200mm wafer surface with Ge2H6+SnCl4, the situation was definitely worse with GeH4+SnCl4. GR were then significantly higher at the wafer edges than close to the center.