Thermal stability of hydrogenated amorphous silicon passivation for p‐type crystalline silicon

Abstract

The thermal stability of hydrogenated amorphous silicon‐passivated monocrystalline silicon wafers is investigated at different annealing times and temperatures. Stepwise thermal annealing was performed at temperatures ranging from 100 to 500 °C for 1, 5 and 15 min, respectively, and the effective minority carrier lifetime was measured after each annealing step using carrier density imaging. Annealing at lower temperatures up to 250 °C results in a significant improvement of the effective carrier lifetime compared with that of as‐deposited samples, increasing to a maximum value of ∼1.5 ms after annealing the sample at 200 °C for 15 min. Annealing at temperatures from 350 °C and upwards results in a reduction of the effective carrier lifetime of all samples. The temperature dependence of the effective lifetime after annealing was investigated by separating the temperature into in three separate ranges; activation‐, peak‐ and degradation. The limits of the activation and degradation temperature: were obtained through annealing experiments. The activation energy for the process responsible for the lifetime improvement was found to be 0.2 eV. An initial degradation energy around 2.1 eV was obtained for degradation process, which can be correlated with H effusion.