SEQUENTIAL OPTICAL STUDY OF THE COMPONENT LAYERS OF A SEMICONDUCTOR QUANTUM-WELL SYSTEM

The constituent layers of an InGaAs-GaAs single quantum well were studied systematically and sequentially using photoluminescence, photovoltaic, and electroluminescence techniques. Spectra were obtained first on the base of the device, a heavily silicon-doped GaAs substrate, then on the substrate plus the undoped-GaAs buffer layer, and finally on the complete device consisting of the substrate, buffer layer, single metal-organic vapour phase expitaxially grown In0.13Ga0.87As quantum well (width 5.0 nm), and a GaAs cap layer. Such separate optical spectra may be required to assess the origin of spectral features when the energy of quantum-well transitions are coincident with the energies of possible transitions in the cladding layers. The results showed that when for instance, experimental conditions permit the excitation of the substrate, peaks of substrate origin whose amplitude is comparable with that of the fundamental peak of quantum-well origin (11H) could be observed. In photoluminescence, long-wavelength excitation or a thin buffer layer may enhance emission from the underlying substrate. The nature of the contact used in the electroluminescence and photovoltaic effects may also influence the relative response of the component layers. Finally, a convenient method is developed to calculate the energies of the levels in a single quantum well, as functions of the well width, for a given alloy composition and temperature.