Crystallization of Hydrogenated Amorphous Silicon Thick Films on Molybdenum Substrates

Abstract

Crystallization of hydrogenated amorphous silicon thick films deposited by dc glow discharge on molybdenum substrates was studied by Raman scattering and x-ray diffraction. Investigation was made as a function of amorphous silicon film deposition temperature. On heating the films at a rate of 5 °C/min to 650 °C for various times, it was observed that the film deposited at 300 °C started crystallization faster than the film deposited at 150 °C. The degree of cirystallinity increased with increasing annealing time for all the films. However, at all annealing times, the degree of crystallinity for the annealed film deposited at 150 °C was higher than that of the annealed film deposited at 300 °C, indicating that the crystallization growth rate was higher for the film deposited at a lower temperature. These results were consistent with the dark conductivity measurements. The film deposited at 150 °C showed a photoresponse which increased with increasing annealing time whereas no photoresponse was observed for the film deposited at 300 °C. This was probably due to the degree of crystallinity and grain size being much larger for the film deposited at 150 °C than the film deposited at 300 °C.

Effect of Deposition Temperature on the Photoresponse of Crystallized Hydrogenated Amorphous Silicon Films

“…From the XRD spectra, it was observed that for all the deposition temperatures (150, 225, 275, 300 and 350 oc), the films after laser annealing showed the presence of 111, 220 and 311 Si peaks and the grain size of the laser annealed films calculated from the full width at half maximum of the 111 peak was greater than 2000 A (the limit of grain size as measured by XRD). The degree of crystallinity increased with decreasing deposition temperature for the laser annealed films similar to that observed in the furnace annealed films (650 oC, 50 h) [13]. This increase in the degree of crystallinity for the furnace annealed films was consistent with the increase in conductivity, photoconductivity and photoresponse of these films (Table 1).…”

“…Increasing the grain size and/or passivating the dangling bonds in the grain boundaries by hydrogen could improve the photoresponse of the polysilicon solar cell. There has been no systematic study on the correlation between structural properties and the photoresponse of the resulting polysilicon film obtained after crystallization of a-Si:H. In our previous work [13], we observed that the a-Si:H film deposition temperature plays a major role on the photoresponse of the polysilicon film obtained by the crystallization of dc glow discharge a-Si:H film by furnace annealing. We found that the increase in grain size and crystallinity with decreasing aSi:H deposition temperature improved the photoresponse.…”

“…During annealing, the sample stage was translated in a direction perpendicular to the laser beam by a DC step motor in order to obtain a quasicontinuous laser scan. The experimental details for solid phase crystallization by isothermal furnace annealing had been previously reported [13].…”

“…Effect of amorphous silicon deposition temperature on the electrical properties of the resulting polysilicon films obtained by laser annealing (12 J/cm 2 scanned at 0.45 mm/s) and isothermal furnace annealing at 650 oC (50 h)[13].…”