Low Contact Resistivity to Ge Using In-Situ B and Sn Incorporation by Chemical Vapor Deposition

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 B
₂
H
₆
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.