Rapid thermal-plasma annealing of ZnO:Al films for silicon thin-film solar cells

Abstract Rapid thermal annealing of sputter-deposited ZnO and Al-doped ZnO (AZO) films with and without an amorphous silicon (a-Si) capping layer was investigated using a radio-frequency (rf) argon thermal plasma jet at atmospheric pressure. The resistivity of bare ZnO films on glass decreased drastically from 10 6 to 10 3 Ω·cm at maximum surface temperatures T max above 650 °C, whereas the resistivity increased from 10 − 4 to 10 − 3 –10 − 2 Ω·cm for bare AZO films. On the other hand, the resistivity of AZO films with a 30-nm-thick a-Si capping layer remained below 10 − 4 Ω·cm, even after TPJ annealing at a T max of 825 °C. X-ray diffraction and X-ray photoemission electron studies revealed that the film crystallization of both AZO and a-Si layers was promoted without the formation of an intermixing layer. Additionally, the crystallization of phosphorous- and boron-doped a-Si layers at the sample surface was promoted, compared to that of intrinsic a-Si under identical plasma annealing conditions. The role of the a-Si capping layer on sputter-deposited AZO and ZnO films during TPJ annealing is demonstrated. The effects of the mixing of phosphorous and boron impurities in a-Si:H during TPJ annealing of flat and textured AZOs are also discussed.