Metal organic vapor phase epitaxy growth mechanisms of gallium antimonide and compositional grading in pseudomorphic gallium arsenide antimonide films

The metal-organic vapor-phase epitaxy (MOVPE) of GaSb was studied by measuring vertical and lateral growth rates for varying reactor temperatures and precursor mole fractions for the growth chemistries of trimethyl gallium (TMG)/trimethyl antimony (TMSb) and triethyl gallium (TEG)/TMSb. A Langmuir-Hinshelwood mechanism, consistent with experimental data, involving the surface reaction of monomethyl gallium (MMG) and monomethyl antimony (MMSb) was proposed for the TMG/TMSb case. For the TEG/TMSb case a similar mechanism involving the surface reaction of diethyl gallium (DEG) and Ga with MMSb was proposed which was consistent with the experimental data. The proposed mechanisms, kinetic rate data from literature, and reactor geometry and conditions were then incorporated into a finite element simulation to gain further insight into conditions at the growth surface. TMG/TMSb results showed that lateral growth rates are extremely sensitive to small changes in the precursor mole fractions and exhibit two temperature regimes; a low temperature regime where lateral growth is limited by decomposition of adsorbed MMG and a high temperature regime where lateral growth trends are ascribed to desorption of MMG. TMG/TMSb lateral growth results exhibit an absence of observable surface chemistry effects. TEG/TMSb lateral growth results indicate that [01¯1¯] surfaces have higher growth rates than [01¯1] surfaces, display trends similar to vertical growth for varying precursor mole fractions, and exhibit a single growth temperature regime where lateral growth behavior is attributed to desorption of DEG.;Compositional grading in pseudomorphic GaAs1-ySb y films was studied by comparing measured and simulated x-ray diffraction spectra of GaAs/GaAs1-ySby superlattices grown using various gas switching sequences during interlayer growth pauses. Deposition of a precise Sb overlayer prior to antimonide growth, the subsequent removal of the Sb overlayer by means of desorption, or "chemical flashoff", prior to non-antimonide growth, and a combination of arsenic-for-antimony exchange and surface roughening upon exposure of an antimonide surface to arsine were found to be key phenomena affecting the grading in pseudomorphic GaAs1-ySby films. Lattice-latching, a thermodynamic effect whereby alloy compositions are pinned near lattice-matched values during epitaxial growth, caused pseudomorphic GaAs1-ySby to contain y ≈ 0.20 while thick, relaxed GaAs1-ySb y layers grown under identical conditions contain y ≈ 0.40.