Transmission electron microscopy (TEM) and photocurrent (PC) measurements were carried out to investigate the microstructural properties and excitonic transitions in InxGa1-xAs/In0.52Al0.48As multiple quantum wells (MQWs) for x = 0.54, 0.57 and 0.60. TEM images showed that high-quality 11-period InxGa1-xAs/In0.52Al0.48As MQWs had high-quality heterointerfaces. The results for the PC spectra at 300 K showed that the peaks corresponding to the excitonic transitions from the ground state electronic sub-band to the ground state heavy-hole band (E-1-HH1) and the ground state electronic sub-band to the ground state light-hole band (E-1-LH1) became closer to each other with decreasing In mole fraction and that E-1-HH1 and E1LH1 excitonic peaks shifted to longer wavelength with increasing applied electric field. The calculated values of the E-1-HH1 interband transition energies were in qualitative agreement with those obtained form the PC measurements with and without applied electric field. These results can be helpful in understanding potential applications of InxGa1-xAs/InyAl1-yAs MQWs dependent on In mole fraction and applied electric field in long-wavelength optoelectronic devices. (c) 2005 Elsevier B.V. All rights reserved.