Homoepitaxial Si films were deposited using an ArF excimer laser beam parallel to the substrate to photodissociate Si2H6 at low temperatures (250–350 °C) under laser intensity and Si2H6 partial pressure conditions that result in low initial photofragment concentrations (< 1013 cm−3). Total pressure and flow conditions were chosen such that there is little secondary photolysis of the initial photofragments. The deposition yield of solid Si from photoexcited Si2H6 is estimated to be 0.20±0.04, indicating that in order for film growth to result solely from the primary products in ArF laser (193 nm) photolysis of Si2H6, a sticking coefficient ≥0.6 must be assigned to the dominant growth precursor. Growth rates vary linearly with laser intensity and Si2H6 partial pressure over a range of 1–15 mJ/cm2 pulse and 5–40 mTorr, respectively. Increasing the distance between the laser-beam axis and the silicon substrate results in a reduction of the growth rate that can be explained by gas-phase chemical reaction of the growth precursors as they diffuse to the substrate. Epitaxy is maintained for temperatures above the threshold for thermal decomposition of surface (SiH2)n chains at ∼250 °C, and for temperatures below the onset of Si2H6 pyrolysis and rapid thermal desorption of surface H2 at ∼350 °C.

We have demonstrated improvement of ON/OFF ratio and reduction of leakage current in polysilicon thin film transistors by (A) inserting a thin polycrystalline silicon-germanium layer in the middle of the channel to confine the carriers away from the highly defective polysilicodsilicon-dioxide interface by using the bandgap offset in the valence band, and (B) introducing nearintrinsic regions at the source/drain ends of the channel to reduce the peak lateral electric field in the channel, thereby reducing field emission through grain boundaries.

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