Effects of Si layer thickness on solid-phase crystallization of stacked Ge/Si/SiO₂ structures

The effects of amorphous-Si (a-Si) layer (thickness: 0-20 nm) insertion on low-temperature (<450 °C) solid-phase crystallization of a-Ge films (50 nm) were investigated. Upon the insertion of an ultrathin (<3 μm) a-Si layer, incubation time increased and saturated crystallinity slightly increased. On the other hand, upon the insertion of a thick (>10 μm) a-Si layer, incubation time significantly decreased and saturated crystallinity decreased. Grain sizes obtained at 425 °C were ̃200 and ̃50nm upon the insertion of a-Si layers of 3 and 20 nm, respectively, which agrees with the results for saturated crystallinity. Moreover, upon the insertion of an intermediate-thickness (5-7 nm) a- Si layer, the nucleation rate and saturated crystallinity increased. These phenomena were explained on the basis of the Si-concentration profiles at interfaces. Thus, interface modulation is effective for realizing large-grain polycrystalline Ge.