Strain-induced electrically active stoichiometric defects in InAs y P1− y deposited onto (100) InP by gas-source molecular beam epitaxy

InAsyP1−y epilayers were deposited by gas-source molecular beam epitaxy onto (100) InP, systematically varying the As fraction from 0.15 to 0.75, corresponding to a lattice mismatch of 0.5%–2.4%. Thin (≊190 Å), largely strained InAsyP1−y films exhibit a smooth, planar morphology and good photoluminescence characteristics even for strains exceeding 2%. In thicker films, depending on the growth parameters, capacitance-voltage depth profiling indicates a strain and thickness dependent formation of electrically active defects that results in a net ionized donor concentration with a peak value as high as 2×1019 cm−3 after about 500 Å of growth. Corresponding photoluminescence measurements suggest that these defects are associated with a shallow level about 10 meV below the conduction band edge of the InAsyP1−y. As the thickness further increases, the net residual donor concentration reduces to <3×1015 cm−3 near the top surface of 1.2-μm-thick epilayers with y≤0.6.