ASSESSMENT OF CLUSTERING INDUCED INTERNAL STRAIN IN ALLNAS ON INP GROWN BY MOLECULAR-BEAM EPITAXY

Low-temperature photoluminescence (PL) and Raman measurements were per formed on AlInAs grown lattice matched to InP by molecular beam epitax y at reduced growth temperature (T(s)), The PL of layers grown at T(s) above 500-degrees-C is dominated by excitonic emission, whereas for l ower T(s) donor-acceptor related transitions prevail. Below a critical T(s) of 450-degrees-C a marked shift towards lower emission energies with a maximum shift near 400-degrees-C is observed that is attributed to a modified band edge due to clustering. Comparable trends are dete cted by Raman spectroscopy. The observed reduction of the separation o f the InAs- and AlAs-like longitudinal optical phonon modes (LO(InAs) and LO(AlAs)) demonstrates local internal strain to be present as a re sult of clustering. This effect reaches a maximum for T(s) at 400-degr ees-C. A shift of the LO(InAs) solely accounts for this behavior. In a ddition strong asymmetric broadening of the LO(AlAs)-phonon line obser ved on low T(s) material indicates an increasing reduction of the corr elation length and suggests the structural disorder to be correlated w ith the AlAs sublattice. Taking into account the pressure dependence o f the AlInAs energy gap and the frequency shift of the LO(InAs) phonon , the local internal strain equivalent pressure was calculated from th e PL and Raman results, respectively, giving similar values of up to 5 kbar for material grown at 400-degrees-C.