N-type ZnS:Al thin films prepared by sulfurization of radio frequency sputtered ZnO:Al

Cubic zinc sulfide (ZnS) thin films with the (111) preferred orientation were prepared by sulfurization of radio frequency sputtered ZnO:Al films. The Al-doped ZnS films were annealed in argon to improve the film crystallinity and activate the dopant atoms. The surface morphology, and structural, optical and electrical properties were characterized by scanning electron microscopy, x-ray diffraction, optical transmittance and electrical measurements before and after the ZnO:Al samples were sulfurized and annealed. The results show that the hexagonal ZnO:Al films completely transform into cubic ZnS after being sulfurized in H2S at 550 °C for 2 h. The crystallinity of the ZnS films is improved and the dopant atoms are electrically activated by the thermal annealing at higher temperatures. The resistivity of the ZnS films reaches as low as ∼0.4 Ω cm. This suggests the potential applications of ZnS in certain optoelectronic devices. (paper)