High-pressure photoluminescence study of the electronic structure of InP/GaP quantum dots

The electronic subband structure of self-assembled InP/GaP quantum dots (QDs) has been investigated by means of photoluminescence (PL) measurements as a function of hydrostatic pressure up to 8 GPa and temperature. At ambient pressure the PL emission of the sample arises from direct optical transitions between the lowest electron and hole Gamma-point states confined in the QDs. At a very low pressure of about 0.15 GPa, the Gamma-X conduction band crossover occurs, after which the PL emission of the dots becomes roughly 20 times weaker in intensity and its energy exhibits the slight redshift typical of indirect recombination processes from the conduction band X valleys. Our results indicate a type-I band alignment for the strained InP/GaP dot structure at low pressure and yield a value of 300 +/- 30 meV for the valence-band offset.