Superlattices and Microstructures, Vol. 21, No. 4, 1997 Coupled ultrathin InAs layers in GaAs as a tool for the determination of band offsets J. Br¨ ubach, A. Yu. Silov, J. E. M. Haverkort, W. van der Vleuten, J. H. Wolter COBRA Interuniversity Research Institute, Eindhoven University of Technology, Department of Physics, P.O. Box 513, 5600 MB Eindhoven, The Netherlands (Received 15 July 1996) We have determined the band offsets at the highly strained InAs/GaAs heterointerface by photoluminescence excitation (PLE) measurements of the symmetric and antisymmetric states in two coupled ultrathin InAs layers embedded in a GaAs matrix. The conduction band offset E c could be separated from the valence band offsets, since in a 32 monolayer (ML) barrier sample, the splitting between the heavy-hole exciton transitions is solely determined by E c . Knowing E c , the heavy-hole (hh) and light-hole (lh) band offsets E hh and E lh could subsequently be determined from the coupling-induced shift and splitting in samples with a 16, 8 and 4 ML barrier. We find a conduction band offset of 535 meV, a conduction band offset ratio of Q c = 0.58 and a strain induced splitting between the hh and lh subbands of 160 meV. c  1997 Academic Press Limited Key words: strained quantum wells, band offsets, ultrathin InAs layers. 1. Introduction The magnitude of the band offsets in compressively strained ultrathin InAs layers embedded in a GaAs matrix is a subject of recent interest. Up to now, a procedure for a straightforward separation of the conduction and valence band offsets was missing, resulting in a large spreading of the band offsets reported previously [1 – 3] . Moreover, the excitonic character of the observed optical transitions and the strong dependence of the exciton binding energies on the InAs layer thickness [1] had not been considered in the band offset determination. Finally, all band offsets determined up to now employed the square-well model to calculate the confined energy levels. This approach cannot be justified for InAs layers of monolayer thickness. In this paper we determine the band offsets using two coupled ultrathin InAs layers separated by a GaAs barrier. Due to coupling, the confined electron, hh- and lh-states are split into symmetric and antisymmetric states, in the following denoted as e ± , hh ± and lh ± , respectively (see Fig. 1 A). When the effective masses and the thickness of the InAs layer and GaAs barrier are known, the energy splitting between the symmetric and antisymmetric states directly yields the band offsets. Moreover, E c could be determined independently from E hh since the hh + –hh − splitting is zero in a 32 ML GaAs barrier sample due to the large hh effective mass and the large barrier thickness. Finally, additional uncertainty due to excitonic effects could be eliminated, 0749–6036/97/040527 + 06 $25.00/0 sm960177 c  1997 Academic Press Limited