Electrical and Structural Properties of Crystallized Amorphous Silicon Thin Films

Polycrystalline-silicon thin films on inexpensive substrates provide a low-cost and straightforward method for the fabrication of inexpensive solar cells. Aluminum-induced crystallization (AIC) of a-Si can result in polysilicon thin films with favorable electrical and optical properties, which can be used to fabricate solar cells with relatively high efficiency. This technique was used in this work to crystallize various types of amorphous silicon thin films: intrinsic a-Si:H on glass substrates created by PECVD, sputtered a-Si on glass substrates, and sputtered a-Si on c-Si substrates. The impact of annealing temperature and duration on the crystallization process was studied using different techniques such as; SEM, EDAX, and XRD. The Annealing temperature varied from 250 degrees C to 350 degrees C and the duration varied from 15 min. to 135 min. Crystallization of a-Si:H films occurred at annealing temperature of 250 degrees C even for short time of 15 min. The minimum annealing temperature and time required to produce crystallization of sputtered a-Si was much higher and depends on substrate type. Where films on c-Si substrates require higher temperature to crystallize than film on glass substrates. Based on annealing temperature and duration, the resistivity of a-Si:H ranges from 0.06 to 0.16 omega-cm. The resistivity, carrier concentration, and Hall mobility values for studied films were measured and compared to those previously reported in the scientific literature.