Electrical characterization of SiGeSn grown on Ge substrate using ultra high vacuum chemical vapor deposition

There has been recently considerable interest in growing Si$_{y}$Ge$_{1-x-y}$Sn$_{x}$ alloys for the fabrication of photonic devices that could be integrated with Si technologies. We report temperature dependent Hall (TDH) measurements of the hole concentration and mobility from high quality p-type doped Si$_{0.08}$Ge$_{0.90}$Sn$_{0.02}$ layers grown on p-type doped Ge substrates using ultra high vacuum chemical vapor deposition. The TDH measurements show the hole sheet density remains constant at low temperatures before slightly decreasing and dipping at $\sim $ 125 K. It then exponentially increases with temperature due to the activation of shallow acceptors. At temperatures above $\sim $ 450 K, the hole sheet density increases sharply indicating the onset of intrinsic conduction in the SiGeSn and/or Ge layers. To extract the electrical properties of the SiGeSn layer alone, a parametric fit using a multi layer conducting model is applied to the measured hole concentration and mobility data. The analysis yields boron and gallium doping concentrations of 3x10$^{17}$ cm$^{-3}$ and 1x10$^{18}$ cm$^{-3}$ with activation energies of 10 meV and 11 meV for the SiGeSn layer and Ge substrate, respectively. Furthermore, a temperature independent hole sheet concentration of $\sim $5x10$^{15}$ cm$^{-2}$ with a mobility of $\sim $250 cm$^{2}$/Vs, which is believed to be due to an interfacial layer between the SiGeSn layer and the Ge substrate, is also determined.