Dissolution of donor-vacancy clusters in heavily doped n-type germanium via millisecond annealing

The n-type doping of Ge is self-limiting process due to formation of the vacancy-donor complexes (Dn V with n≤4). Here we report on experiments and density functional theory (DFT) calculations solving the basic problem of donor deactivation in heavily doped Ge. The self-healing process of heavily doped n-type Ge is achieved by rear-side flash lamp annealing (r-FLA) for 20 ms with the peak temperature of about 1050 K. The positron-annihilation lifetime spectroscopy (PALS) reveals that the P4V clusters are main defects in the as-grown Ge:P samples. Millisecond range high-temperature treatment dissociates the phosphorus-vacancy cluster (P4V) and, as shown by SIMS, fully supress the P diffusion. The electrochemical capacitance-voltage (ECV) profiling shows that the effective carrier concentration in P doped Ge (P concentration - 1×1020 cm-3) increases from about 3×1019 cm-3 in as-grown sample to above 8×1019 cm-3 after r-FLA. For the first time using structural (PALS, SIMS) and electrical (ECV) characterization combined with DFT calculations we were able to addressed, explained and solved the fundamental problem hindering the full integration of Ge with CMOS technology.