TRANSMISSION ELECTRON-MICROSCOPY OBSERVATION OF POLYMORPHIC EPITAXIAL-GROWTH OF YSI2-X LAYER IN AL(001) YSI2-X/SI(001) SYSTEMS/

The structures of compounds in the heteroepitaxial system Al/YSi2-x/Si have been examined by high resolution transmission electron microscop y. YSi2-x grown in two stages by a template method consists of two pha ses. Hexagonal YSi2-x(1(2) over bar0$) (low-temperature phase) grows o n Si(001) when Y is deposited at 330 degrees C and then annealed at 50 0 degrees C for 10 min. Subsequent deposition of Y at 330 degrees C fo llowed by annealing at 330 degrees C for Ih results in the growth of t etragonal YSi2-x(001) (high-temperature phase) on the hexagonal phase. The growth of Al(001) on YSi2-x is confirmed. The epitaxial relations hip onalYSi(2-x)[100]//hexagonalYSi(2-x)[100]//Si[110] is found in thi s system. It is also revealed that in the formation process of YSi2-x, the tetragonal phase is nucleated first from a supercooled melt in th e solid phase and then the hexagonal phase is formed by a polymorphic transformation during annealing at appropriate temperatures for the tr ansition.