A detailed study of InAs/InGaAs quantum dots in quantum well (DWELL) structures grown on GaAs substrates for infrared photodetectors was performed using surface photovoltage (SPV) spectroscopy. Three types of samples were investigated: as-grown, and annealed with dielectric coating SiO 2 or SiN. The annealing resulted in intermixing of the material components. The amplitude and phase SPV spectra were measured at room temperature under various experimental conditions. The comparison of the SPV with the photoluminescence (PL) spectra allows one to conclude that the spectral features are due to optical transitions in the DWELL structure. The blueshift observed of these features in the intermixed samples implies that the energy levels responsible for the transitions change correspondingly due to the intermixing process. The interface band-bending in the samples and the mechanisms of the carrier dynamics were determined by a comparative analysis of the SPV amplitude and phase spectra, using our vector model for representation of the SPV signal. © Published under licence by IOP Publishing Ltd.