Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p-and n-type doped regions for both planar and tridimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1×10 19 cm −3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3×10 15 cm −2 and electron concentration of about 4×10 19 cm −3 . The optical and structural properties of ionimplanted GeSn layers are comparable with the in situ doped MBE grown layers.
Highly scaled nanoelectronics requires effective channel doping above 5×10 19 cm −3 together with ohmic contacts with extremely low specific contact resistivity. Nowadays, Ge becomes very attractive for modern optoelectronics due to the high carrier mobility and the quasi-direct bandgap, but n-type Ge doped above 5×10 19 cm −3 is metastable and thus difficult to be achieved. In this letter, we report on the formation of low-resistivity ohmic contacts in highly n-type doped Ge via non-equilibrium thermal processing consisting of millisecond-range flash lamp annealing. This is a single-step process that allows for the formation of a 90 nm thick NiGe layer with a very sharp interface between NiGe and Ge. The measured carrier concentration in Ge is above 9×10 19 cm −3 with a specific contact resistivity of 1.2×10 −6 Ω cm 2 . Simultaneously, both the diffusion and the electrical deactivation of P are fully suppressed.
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