Direct observations of the vacancy and its annealing in germanium

Weakly $n$-type doped germanium has been irradiated with protons up to a fluence of $3\times {10}^{14}$ cm${}^{-2}$ at 35 K and 100 K in a unique experimental setup. Positron annihilation measurements show a defect lifetime component of 272$\pm$4 ps at 35 K in in situ positron lifetime measurements after irradiation at 100 K. This is identified as the positron lifetime in a germanium monovacancy. Annealing experiments in the temperature interval 35–300 K reveal two annealing stages. The first at 100 K is tentatively associated with the annealing of the Frenkel pair, the second at 200 K with the annealing of the monovacancy. Above 200 K it is observed that mobile neutral monovacancies form divacancies, with a positron lifetime of 315 ps.

Figure 1

(a) The higher lifetime component ${\tau }_2$, (b) the lower lifetime component ${\tau }_1$, and (c) the average positron lifetime ${\tau }_{\text{ave}}$. The solid curve has been drawn to guide the eye. The inset shows ${\tau }_2$, ${\tau }_1$, and ${\tau }_{\text{ave}}$ after RT annealing and measured at RT. The open gray symbols for ${\tau }_1$ and ${\tau }_2$ cannot be physically interpreted since the two state trapping model obviously fails below 200 K.

Figure 2

(a) The intensity of the higher lifetime component $I_2$, (b) the higher lifetime component ${\tau }_2$, and (c) the average positron lifetime ${\tau }_{\text{ave}}$. The solid curve has been drawn to guide the eye.

Figure 3

Schematics of the vacancy reactions in the temperature range 35–300 K. The coloring on the vacancies indicates charge state, red negative or transparent neutral, a dashed circle indicates annealing.