Optical properties of InP/InAlAs/InP grown by MOCVD on (100) substrates: influence of V/III molar ratio

We report on the optical study of double heterostructures InP/InAlAs/InP grown on (100) substrates at various V/III molar ratios, grown by metal-organic chemical vapor phase epitaxy (MOCVD). Photoluminescence experiments have been performed to investigate the optical transitions in these samples. In order to identify the optical transition at inverted interface (InP grown on InAlAs) at 1.25 eV, previously assigned to a type II interface band structure, a study based on transfer matrix technique under the envelope function approximation has been performed. Taking into account the formation of InAsxP1−x thin graded layer located at the inverted interface (between InP and InAlAs), a simulation indicates that this recombination originates in fact from a type II interface band structure between electrons confined on InAsP and holes located on top of the InAlAs valence band. Detailed studies of photoluminescence spectroscopy (PL) properties of InAlAs epilayer at low temperature indicate that the PL spectrum, recorded at low temperature (12 K) on (100) substrate sample with V/III=50, shows double effects: the presence of a clustering and of a natural superlattice (SL) due to composition modulation. For other samples with different V/III, the composition modulation disappears so that only a clustering effect remains.