K. Kirilov

A vector model for analysing the surface photovoltage amplitude and phase spectra applied to complicated nanostructures

An approach is presented for comprehensive and reliable analysis of the surface photovoltage (SPV) amplitude and phase spectral behaviour in various semiconductor materials and structures. In this approach the SPV signal is represented as a radial vector with magnitude equal to the SPV amplitude and angle with respect to the x-axis equal to the SPV phase. This model is especially helpful in complicated nanostructures, where more than one SPV formation processes arises during the spectrum run. The value of the proposed model has been demonstrated by the successful explanation of seemingly contradictory SPV amplitude and phase spectra of AlAs/GaAs superlattices with embedded GaAs quantum wells, grown on different GaAs substrates. This has provided useful information about the investigated nanostructures. The need for simultaneous examination of both SPV amplitude and SPV phase spectra in order to obtain a correct understanding of the experimental data is emphasized.

A surface photovoltage spectroscopy study of GaAs/AlAs complicated nanostructures with graded interfaces

We present a surface photovoltage (SPV) spectroscopy study of the optical properties and the bound states of graded interface AlAs∕GaAs superlattices (SLs) containing two GaAs embedded quantum wells (EQWs) with different widths. SPV spectra are measured in the metal-insulator-semiconductor operation mode under super-band-gap optical excitation at room temperature. In spite of the relatively large absorption of the GaAs substrate, the SPV spectra exhibit clearly resolved features superimposed on the substrate smooth background. These features have been identified as free exciton transitions in the EQWs and in the SL. This interpretation is based on a detailed comparison of the SPV results with those of electronic structure calculations and photoluminescence spectral measurements. The calculations are performed in frames of the envelope function approximation, employing a model structure very similar to the real one and taking into account the interface grading. The mechanisms of the SPV signal generation h...

Optical properties of thick GaInAs(Sb)N layers grown by liquid-phase epitaxy

We present an experimental and theoretical study of GaInAs(Sb)N layers with thickness around 2 μm, grown by liquid-phase epitaxy (LPE) on n-type GaAs substrates. The samples are studied by surface photovoltage (SPV) spectroscopy and by photoluminescence spectroscopy. A theoretical model for the band structure of Sb-containing dilute nitrides is developed within the semi-empirical tight-binding approach in the sp3d5s*sN parameterisation and is used to calculate the electronic structure for different alloy compositions. The SPV spectra measured at room temperature clearly show a red shift of the absorption edge with respect to the absorption of the GaAs substrate. The shifts are in agreement with theoretical calculations results obtained for In, Sb and N concentrations corresponding to the experimentally determined ones. Photoluminescence measurements performed at 300K and 2 K show a smaller red shift of the emission energy with respect to GaAs as compared to the SPV results. The differences are explained by a tail of slow defect states below the conduction band edge, which are probed by SPV, but are less active in the PL experiment.

An alternative approach to the electronic-structure calculation of crescent-shaped GaAs/AlGaAs quantum wires

An alternative approach for calculating the bound states energies in crescent-shaped GaAs/AlGaAs quantum wires is proposed. We consider carrier confinement in the X and Y directions separately, taking advantage of the fact that the crescent width is much smaller than its length, and varies slowly along the Y direction. The tight-binding method is used in the calculation of the confinement energies in the individual quantum wells, taking into account the real shape of the crescent as well as of the confinement potential along the Y direction.