Implantation and activation of high concentrations of boron in germanium

There is renewed interest in the development of Ge-based devices. Implantation and dopant activation are critical process steps for future Ge devices fabrication. Boron is a common p-type dopant, which remarkably is active immediately after implantation in Ge at low doses. This paper examines the effect of increasing dose (i.e., 5 × 10¹³ - 5 × 10¹⁶ cm^-2) and subsequent annealing (400 °C-800 °C for 3 h in nitrogen) on activation and diffusion of boron in Ge. Secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP), high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA) are used to characterize the implants before and after annealing. It is found that very high fractions of the boron dose (∼5%-55%) can be incorporated substitutionally immediately after implantation leading to very high hole concentrations, ≥ 2 × 10²⁰ cm^-3, deduced from SRP. Small increases in activation after annealing are observed, however, 100% activation is not indicated by either SRP or NRA. Negligible diffusion after annealing at either 400 °C or 600 °C for 3 h was, furthermore, observed.