Structural evaluation of GaAs1_xBix obtained by solid-phase epitaxial growth of amorphous GaAs1_ xBix thin films deposited on (001) GaAs substrates

We have structurally evaluated GaAs1_xBix obtained by solid-phase epitaxial growth of amorphous GaAs1_ xBix thin films via transmission electron microscopy and related techniques. Amorphous GaAs1_xBix layers are obtained using a molecular beam epitaxy apparatus at 180 degrees C. When the amorphous GaAs1_ xBix layer is annealed for 1 h at a medium temperature of 350 degrees C, an epitaxial GaAs1_xBix layer is grown on the GaAs substrate, forming a thick polycrystalline layer between the region above the epi-layer and the GaAs cap layer. In addition, three types of defects are generated in the region above the interface between the epi-layer and the substrate: small As precipitates (approximately 5 nm in diameter) and large zincblende GaAs1_ xBix and rhombohedral Bi precipitates (10-15 nm in diameter). On the other hand, we found that a precipitate-free GaAs1_ xBix epitaxial layer is grown after annealing for 1 h at 600 degrees C, forming only a small amount of zincblende GaAs1_xBix and rhombohedral Bi precipitates (no As precipitates) in the region above the epi/sub interface. Furthermore, the difference between the above results and in the case of low-temperature-grown molecular beam epitaxy GaAsBi crystals after annealing is discussed. We also observed varying features and distributions of the defects in LTG GaAs1_ xBix layers (Tg = 250 degrees C) after annealing for 20 min at 600 degrees C from those of the same in a previous study: 1) rh-As precipitates are generated only at the epi/sub-interface; 2) Type-A (V-shaped) and Type-B (?-shaped) rhBi precipitates are generated in the upper and lower regions of the GaAs1_ xBix layer, respectively. Based on these results, we discussed the origins of the above differences and factors affecting the generation of these precipitates.