The low contact resistivity with the median value of $3.1\times 10^{-{9}}\,\,\Omega \cdot \text {cm}^{{2}}$ (the lowest value of $1.1\times 10^{-{9}}\,\,\Omega \cdot \text {cm}^{{2}}$ ) is achieved by Ti metal contact… Click to show full abstract
The low contact resistivity with the median value of $3.1\times 10^{-{9}}\,\,\Omega \cdot \text {cm}^{{2}}$ (the lowest value of $1.1\times 10^{-{9}}\,\,\Omega \cdot \text {cm}^{{2}}$ ) is achieved by Ti metal contact to in-situ B-doped GeSn with B segregation at Ti/GeSn:B interface. The newly developed two-sheet-resistance model is used to extract the contact resistivity, considering the different sheet resistance of GeSn:B in the gap regions and under the metal layers. Sn incorporation into Ge lowers the Schottky barrier height of holes, and the heavy B doping at the Ti/GeSn:B interface reduces the hole tunneling distance. Fully compressively strained GeSn:B epitaxial layer with the bulk active [B] of $1.9\times 10^{{20}}$ cm−3 and [Sn] of 4.7% on the Ge-buffered Si substrate is successfully grown by chemical vapor deposition. The effects of B2H6 precursor on growth rate and [Sn] are investigated. Low contact resistivity is obtained using conventional B-doping in GeSn grown at a temperature as low as 305 °C and submitted to a post epitaxy thermal budget of 400 °C for 30 s.
