Tunnel-coupled InGaAs/GaAs quantum wells: Structure, composition, and energy spectrum

An integrated approach to the analysis of tunnel-coupled InGaAs/GaAs quantum well heterostructures is suggested. In the approach, both experimental and theoretical investigation methods are used. Transmission electron microscopy combined with energy-dispersive X-ray spectrometry is used to determine the spatial distribution of the InGaAs alloy’s composition. The photoluminescence and photoconductivity spectra of the structures are recorded experimentally. In order to interpret the results in more detail, computer simulation of the epitaxial growth is performed. By simultaneously solving the Schrödinger equation and the Poisson equation, the energy states are calculated for the quantum-confined hetertostructure with initial and real composition profiles. The results of calculations are correlated with the data obtained for interband optical transitions from the analysis of the photoluminescence and photoconductivity spectra. Good agreement between the experimental and theoretical results is gained. The approach suggested in the study provides a means for refining the real geometrical features of the structure, for correlating the spectral results with the real composition profile of the structure, and for correcting the structural and growth parameters to improve the optical characteristics of the structure.