Internal strain and dislocations in Ga_1−xAs crystals grown by liquid phase epitaxy/electroepitaxy

Abstract

Strain relaxed, low dislocation density In_xGa_1−xAs crystals, 0 < x <0.2, have been successfully grown by liquid phase electroepitaxy on the GaAs substrate, despite the crystal/substrate lattice mismatch. Residual strain in these novel substrates is below 10⁻⁴, at least an order of magnitude lower than in the molecular beam epitaxially (MBE) or metalorganic chemical vapor deposition-grown ternary buffer layers of similar composition. Threading dislocation density induced by both the crystal/substrate lattice mismatch and unavoidable composition variations has been reduced from the low 10⁶ cm⁻² range, while growing directly on GaAs, to the mid 10⁴ cm^-2 by employing both the MBE grown ternary buffer layer and selective lateral overgrowth of an SiO₂ mask which, prior to the crystal growth, was deposited on the buffer layer and patterned by photolithography with 10 μm wide, oxide free seeding windows. The full width at half maximum of the rocking curves measured for In_xGa_1−xAs crystals grown by liquid phase epitaxy/electroepitaxy on patterned, closely lattice matched buffer layers was in the 20–23 arc s range. Further reduction of the dislocation density and a more uniform dislocation distribution is expected by modifying the initial growth conditions, improving substrate preparation, and optimizing the seeding window geometry.