Transmission electron microscope study on atomic ordering in GaAs(1-x)Sb(x) grown by molecular beam epitaxy
Abstract
In order to investigate the formation process of ordered phase during thin film growth, GaAs$\sb{0 \cdot 5}$Sb$\sb{0 \cdot 5}$ epilayers grown by molecular beam epitaxy (MBE) have been studied by using transmission electron microscopy (TEM). The semiconductor epilayers were grown on two different substrates, lattice matched (100) InP and lattice mismatched (100)GaAs, at three different temperatures, 480$\sp\circ$C, 520$\sp\circ$C and 580$\sp\circ$C. A 1/2$\{$111$\}$ type long-range ordered phase has been observed in the GaAs$\sb{0 \cdot 5}$Sb$\sb{0 \cdot 5}$ epilayers grown at 580$\sp\circ$C, while a short-range ordered phase exists in epilayers grown at lower temperatures. The atomic arrangement in the long-range ordered phase has been analyzed by the observation of selected area diffraction patterns and high resolution images. The ordered structure is described as an alternative arrangement of As-rich and Sb-rich $\{111\}$ planes in one of $\langle$111$\rangle$ directions. The ordered structure has a trigonal symmetry and belongs to the space group of R3m. An asymmetric formation of the ordered structure is observed in all epilayers observed. Superstructure reflections appear at the positions of h $\pm$ 1/2,h $\pm$ 1/2,1 $\mp$ 1/2 and h $\pm$ 1/2,k $\mp$ 1/2,1 $\pm$ 1/2, but they are not observed at the positions of h $\pm$ 1/2,k $\pm$ 1/2,1 $\pm$ 1/2 and h $\mp$ 1/2,k $\pm$ 1/2,1 $\pm$ 1/2. Based on the analysis of growth conditions, it is suggested that the origin of the asymmetry is the surface atomic structure in the growing surface, which has different bonding structures between (011) and (011) axes. The evolution of the ordered microstructures with growth temperature has been studied by the observation of dark field images, high resolution images and diffuse scattering. The observations have shown the existence of plate-shaped microdomains of ordered phase which are parallel to the growth plane and embedded in the disordered matrix. The results of the present study indicate that surface kinetic processes play major role in the formation of the ordered phase. Based on these observations, along with those made in other recent studies, the nature of the ordered phase in III-V semiconductor systems are discussed.
Degree
Ph.D.
Advisors
Otsuka, Purdue University.
Subject Area
Materials science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.