Synthesis of narrow band-gap III-V semiconductors using metal-organic vapor phase epitaxy

The synthesis of narrow band gap materials in particular InAs, GaSb and InSb has been studied using metal-organic vapor phase epitaxy (MOVPE). Typically, for device applications these materials are grown on SI GaAs substrates. The integration of these materials with GaAs substrates through direct epitaxial growth is plagued by the high density of defects that are formed due to the 7-14% lattice mismatch between these materials. The presence of high density of threading dislocations in the resultant films has necessitated the development of approaches that alter the primary mechanisms of defect introduction and propagation, consequently leading to a reduction in the overall threading dislocation density during lattice-mismatched growths. Selective area epitaxy on nano-patterned substrates generated using block copolymer lithography was employed to nucleate the growing epitaxial material within specific mask openings and lead to strain relaxation within small islands. A significant improvement in material properties was observed for GaSb films grown on nano-patterned GaAs substrates at a very early stage of film growth. The FWHM of the GaSb peak grown on nano-patterned GaAs substrates was reduced by a factor of two or more relative to the films grown to the same thickness on non-patterned GaAs substrates. Defect mitigation was achieved for InAs growth on nano-patterned GaAs templates however, the resultant films exhibited a very different growth behavior when compared to GaSb growth on GaAs templates. While 200 mn thick GaSb film on nano-patterned GaAs substrates yielded a smooth, planar morphology, large islands were observed for InAs growth on nano-patterned GaAs templates. The difference in surface morphology between these systems was attributed to the enhanced surface diffusion of the indium adatoms combined with the kinetics of strain-relaxation leading to a disparity in island growth rate. From this study, it was determined that a balance between surface transport and strain-derived non-uniformity in island growth must be reached through careful choice of growth parameters for obtaining films with planar morphologies during lattice-mismatched integration.