Distribution of Charge Carrier Concentrations in Epitaxial Ge and GeSn Layers Grown on N-=Sup=-+-=/sup=--si(001) Substrates

Heteroepitaxial Ge or Ge1-xSnx layers were grown by hot-wire chemical vapor deposition on Si(001) substrates doped heavily with a donor (As or Sb) impurity. The same layers were also grown on high-resistance Si(001) substrates for comparison. The depth profiles of carrier concentration were measured in both types of layers using the capacitance-voltage method, and carrier mobilities were measured additionally by the Hall effect method in layers on high-resistance silicon. It was found that the layers grown on high-resistance substrates were p-type, while the layers grown in the same regimes on heavily doped substrates were n-type with electron concentration n=(4-9)·1016 cm-3 in Ge layers and n=(2-4)·1017 cm-3 in GeSn layers. It was established experimentally and theoretically that the effect of autodoping of Ge and GeSn layers is lacking in the hot-wire chemical vapor deposition method. In our view, the growth of n-type Ge and GeSn layers on n+-Si(001) substrates doped heavily with a donor (As or Sb) impurity is associated with the segregation of this impurity in the process of growth of a buffer Si layer and its subsequent incorporation into growing Ge or GeSn layers. Keywords: epitaxy, doping, Ge, Si, Sn, concentration.