In situ ohmic contact formation for n-type Ge via non-equilibrium processing.

Highly scaled nanoelectronics requires effective channel doping above 5 × 10¹⁹ 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 × 10¹⁹ 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 × 10¹⁹ cm⁻³ with a specific contact resistivity of 1.2 × 10⁻⁶ Ω cm². Simultaneously, both the diffusion and the electrical deactivation of P are fully suppressed. [ABSTRACT FROM AUTHOR]