Interface roughness characterization by electron mobility of pseudomorphic In 0.74 Ga 0.26 As ∕ In 0.52 Al 0.48 As modulation-doped quantum wells grown on (411)A InP substrates by molecular beam epitaxy Extremely high electron mobility of pseudomorphic In 0.74 Ga 0.26 As ∕ In 0.46 Al 0.54 As modulation-doped quantum wells grown on ( 411 ) A InP substrates by molecular-beam epitaxy Appl. Phys. Lett. 85, 4043 (2004); 10.1063/1.1807023Super-flat interfaces in pseudomorphic In 0.72 Ga 0.28 As/In 0.52 Al 0.48 As quantum wells grown on (411)A InP substrates by molecular beam epitaxy In 0.18 Ga 0.82 As/GaAs 1−y P y quantum wells grown on (n11) A GaAs substrates by molecular beam epitaxy Larger critical thickness determined by photoluminescence measurements in pseudomorphic In 0.25 Ga 0.75 As/Al 0.32 Ga 0.68 As quantum well grown on (411)A GaAs substrates by molecular beam epitaxy In 0.53 Ga 0.47 As/ AlAs 0.56 Sb 0.44 quantum well ͑QW͒ structures were grown on a ͑411͒A oriented InP substrate by molecular-beam epitaxy ͑MBE͒. Photoluminescence ͑PL͒ spectra at 12 K indicated that interface flatness of a 2.4 nm thick In 0.53 Ga 0.47 As QWs on the ͑411͒A InP substrate, which can be utilized for 1.55 m range all-optical-switching devices using intersubband transition ͑ISBT͒, is much superior to that of QWs simultaneously grown on a conventional ͑100͒ InP substrate over the whole range of the growth temperature ͑T s = 480-570°C͒. The best value of full width at half-maximum of a PL peak ͑12 K͒ from the 2.4 nm thick In 0.53 Ga 0.47 As/ AlAs 0.56 Sb 0.44 QW grown on the ͑411͒A InP substrate at 570°C was 36 meV, which is much smaller than the best value previously reported ͑58 meV͒ for similar ͑100͒ In 0.53 Ga 0.47 As/ AlAs 0.56 Sb 0.44 QWs. This result indicates that MBE growth of In 0.53 Ga 0.47 As/ AlAs 0.56 Sb 0.44 QWs on the ͑411͒A InP substrate significantly improves their interface flatness and 1.55 m range In 0.53 Ga 0.47 As/ AlAs 0.56 Sb 0.44 ISBT devices fabricated on the ͑411͒A InP substrate are expected to provide much better performance.