Thermal annealing effects on the optical and electrical properties of a-SiC: H thin films sputtered at different hydrogen flow rates

In this paper we study the effect of annealing process on the optical and electrical properties of the a-SiC:H thin films sputtered at three different hydrogen flow rates 9 sccm, 14 sccm and 20 sccm. Optical transmission measurements have shown that the optical band gap, E-g, is affected by thermal annealing when T-a > 575 degrees C, due to emission of hydrogen bonded to silicon. For hydrogen flow rate 9 sccm, the evaluation of the optical and electrical measurements have shown that for 400 degrees C < T-a <= 550 degrees C the quality of the a-SiC:H thin films presents a reasonable improvement, with the optimum result been achieved at T-a = 550 degrees C remaining there up to 575 degrees C. This behavior is attributed to the relaxation of the strain in the amorphous network. Further increase of T-a causes emission of hydrogen bonded to silicon, leading to rapid deterioration of the properties of the amorphous semiconductor. As the hydrogen flow rate increases from 9 sccm to 20sccm, the optimum material quality is achieved at higher T-a since the emission of a small quantity of hydrogen enables additional relaxation in the amorphous network. Finally, the maximum values of photosensitivity of the annealed a-SiC:H thin films (congruent to 1500) in combination with the corresponding values of E-g make these films very interesting for applications as optical sensor devices and solar cells.