Surface photovoltage studies of ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ and ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}{\mathrm{As}}_{1-y}{\mathrm{N}}_y$ quantum well structures

Surface photovoltage in GaAs-based type I strained quantum well structures is discussed. First, a model for the photovoltage generation in our samples is presented. Then surface photovoltage spectra of two structures, GaAs/InGaAs/GaAs and GaAs/InGaAsN/GaAs, are analyzed. The samples show four steplike main features in the spectrum. The InGaAs sample shows also excitonic peaks associated with some of the steps. To explain the spectra, a comparison with calculations and photoluminescence measurements is made. For photon energies under the barrier band gap, the photovoltage is generated due to the optical absorption in the quantum well. To account for the magnitude of the photovoltage in this case, carriers must escape out of the quantum well. We propose and discuss three such carrier excitation-escape mechanisms. We discuss the role of an optical transition involving confined and extended states in the surface photovoltage spectra. By analyzing the temperature dependence of the spectra we come to the conclusion that the transitions involving extended states play an essential role in the photovoltage generation in our quantum well (QW) samples. This allows the determination of the band alignment of QW structures. We find that by adding 1,7% N in ${\mathrm{In}}_{0.35}{\mathrm{Ga}}_{0.65}\mathrm{As}$ strained quantum wells, the energies of the valence band maximum and conduction band minimum are lowered by 43 and 140 meV, respectively, at room temperature.