Flash-lamp-induced explosive crystallization of amorphous germanium films leaving behind periodic microstructures

Abstract

Flash lamp annealing (FLA) can induce the explosive crystallization (EC) of micrometer-order-thick amorphous germanium (a-Ge) films. This EC leaves behind periodic microstructures consisting of two regions with different grain features existing alternatively along a lateral crystallization direction. One of the two regions contains a few hundred nm-sized relatively large grains, while such large-sized grains are not seen in the other region. This particular microstructure is similar to that of polycrystalline silicon (poly-Si) films formed through EC induced by FLA. The interval of the periodic structures in the polycrystalline Ge (poly-Ge) of 0.7–0.85μm is smaller than that in the case of Si of about 1μm. This is probably due to larger thermal diffusivity of a-Ge than that of a-Si. The speed of the EC is estimated to be 5–7m/s, which is smaller than the speed of liquid-phase-epitaxy- (LPE-) based EC of ~8m/s for Ge films reported previously. This fact indicates that a crystallization process other than LPE is also involved in this EC, and solid-phase nucleation governs the EC. This is also similar to what have been previously confirmed in Si films, meaning that this particular EC could occur universally in a variety of materials.