Structural and Electrical Properties of the Poly-Si Films

In this section, the most important structural (grain size, grain orientation and intragrain defects) and electrical properties of the poly-Si films prepared by the ALILE process are discussed. 

A typical EBSD map of the surface of a poly-Si film on glass prepared by the ALILE process is shown in Fig. 12.9 (left) [39]. The sample was annealed at 425°C for 16h. Afterwards, the Al(+Si) top layer was removed by CMP. The poly-Si film shown here features an average grain size of 7 pm and a maximum grain size of 18 pm. From such EBSD measurements, not only the grain size but also the crystallographic orientation of the grains can be determined. 

A high preferential (100) orientation of the poly-Si surface is favorable for subsequent epitaxial growth at low temperatures [41-43]. Due to the preferential (100) orientation, the utilization of the poly-Si films formed by the ALILE process as a template (seed layer) for subsequent epitaxial thickening at low temperatures is quite attractive [44]. 

Hall effect measurements were used to investigate the electrical properties of the poly-Si films formed by the ALILE process. Due to the incorporated Al, the poly-Si films are always p-type. At room temperature, a hole concentration of 2.6 x 1018 run 3 and a hole mobility of 56.3 cm2 V 1 s 1 were determined [16]. Temperature dependent Hall measurements revealed both valence band conduction and defect band conduction (two-band conduction). For such highly doped material, the presence of a defect band conduction is expected. The Al concentration in the poly-Si films was measured by secondary ion mass spectroscopy (SIMS). An Al concentration of about 3 x 1019 cm 3 was found, which is about a factor of 10 larger than the 

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