Record Low Contact Resistivity to Ge:B (8.1×1010Ω-cm2) and GeSn:B (4.1×1010Ω-cm2) with Optimized [B] and [Sn] by In-Situ CVD Doping

The record low contact resistivity (ρ
_c
) of Ti contact to Ge:B (8.1×10
^-10
Ω-cm
²
) is achieved by in-situ doped CVD using the high-order Ge precursor (Ge
₂
H
₆
). The best achievable [B]act. of 7×10
²⁰
cm
^-3
and extended epitaxial process window are obtained using Ge
₂
H
₆
. By optimizing the [B] and [Sn], 2% Sn addition into Ge epitaxy reaches the lowest p
_c
of 4.1×10
^-10
Ω-cm
²
. Further Sn addition (4.7% and 13.2%) increases ρ
_c
due to reduced [B], and degrades the thermal stability. The record low resistivity (2×10
^-4
Ω-cm) among epitaxial p-type Ge and GeSn is also demonstrated. Optimized metal etching processes ( Cl
₂
+BCl
₃
for metal on GeSn:B, while Cl
₂
for metal on Ge:B) are necessary to minimize etching of GeSn:B and Ge:B, and to fabricate the test structure. A two-sheet-resistance model is used to correctly extract the ρ
_c
. B segregation at the metal/semiconductor interface enables the record low ρ
_c
.