Influence of Growth Temperature on Ordering in InGaAs Grown on (001) InP Using Tertiarybutylarsine Source MOCVD
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I. INTRODUCTION III-V compounds are important in the manufacture of many electronic and optoelectronic devices. These compounds crystallize as the zinc-blende structure and can be described as two interpenetrating face centered cubic sublattices; one consisting of group III atoms the other of' group V. Ternary and quaternary layers are characterized by the solution mixing of two or more components on a specific sublattice. These compounds are generally considered to have a bandgap that is a direct function of the composition. This is true for compounds where the mixed components are randomly distributed. Recently, however, there have been many observed cases where a non-random distribution of species occurs on a particular sublattice. 2 3 Reported deviations from the ideally mixed structure include phase separation , , long-range atomic 24 ordering , and various ordering defects. Bandgap shifts, valence band splitting and mobility variations have been shown to occur with atomic ordering in certain compounds. These observations are significant becaulse they demonstrate an additional degree of freedom for tuning the electronic properties in lattice
matched compositions. Ordering in these compounds has been observed almost exclusively for layers prepared under specific growth conditions. The ordered microstructure is generally recognized as being due to a stable surface configuration becoming quenched into the bulk during epitaxial growth. Many of these microstructures are, in fact, not considered to be stable bulk phases. L I, CuPt type ordering evolves under certain conditions for mixed layers grown on (001) surfaces. Of interest is the occurrence of only two of the four possible ordered variants. This result is attributed to the two-fold nature of the 2x4 reconstructed (001) surface. The direction of growth step propagation is also believed to affect the ordered variant preference; growth on exact (001) oriented surfaces results in both (I 1I) and (I 11l)variants, while vicinal (001) surfaces tend to show only the variant closest to the direction of misorientation. It is critical to control ordering if these materials are used to produce reproducible quality laser or MODFET devices. Experimentally this requires a determination of the growth conditions leading to ordering and an accurate method of determining the degree of order. In this study we prepared epitaxial layers of InGaAs with the intent of optimizing CuPt type ordering. A modified method of measuring order parameter by x-ray diffraction is used to determine the change in ordering with growth temperature.
II. EXPERIMENTAL MOCVD Growth The growth sources used to deposit InGaAs layers on InP substrates were trimethylindium (TMI), trimethylgallium (TMG) and tertiarybutylarsine (TBA); the carrier gas was Pd diffused hydrogen. Two 287 Mat. Res. Soc. Symp. Proc. Vol. 326. @1994 Materials Research Society
types of substrates were used: 1) sulfur doped InP of exact (001) orientation, and 2) iron doped (001) InP with surfaces vicinally misoriented 60 towards a {
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