Assessment of clustering induced internal strain in AlInAs on InP grown by molecular beam epitaxy

Abstract

Low-temperature photoluminescence (PL) and Raman measurements were performed on AlInAs grown lattice matched to InP by molecular beam epitaxy at reduced growth temperature (Ts). The PL of layers grown at Ts above 500 °C is dominated by excitonic emission, whereas for lower Ts donor-acceptor related transitions prevail. Below a critical Ts of 450 °C a marked shift towards lower emission energies with a maximum shift near 400 °C is observed that is attributed to a modified band edge due to clustering. Comparable trends are detected by Raman spectroscopy. The observed reduction of the separation of the InAs- and AlAs-like longitudinal optical phonon modes (LOInAs and LOAlAs) demonstrates local internal strain to be present as a result of clustering. This effect reaches a maximum for Ts at 400 °C. A shift of the LOInAs solely accounts for this behavior. In addition strong asymmetric broadening of the LOAlAs-phonon line observed on low Ts material indicates an increasing reduction of the correlation length and suggests the structural disorder to be correlated with the AlAs sublattice. Taking into account the pressure dependence of the AlInAs energy gap and the frequency shift of the LOInAs phonon, the local internal strain equivalent pressure was calculated from the PL and Raman results, respectively, giving similar values of up to 5 kbar for material grown at 400 °C.