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

Abstract

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 G-point states confined in the QDs. At a very low pressure of about 0.15 GPa, the G-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 AE 30 meV for the valence-band offset.

Recombination dynamics in self‐assembled InP/GaP quantum dots under high pressure

“…The results are discussed in terms of a phenomenological model for carrier relaxation and capture into the dots, which takes into account the pressure dependence of the electronic band structure, as determined previously in Refs. [2,3].…”

“…With increasing pressure, however, first occurs the conduction band Γ -X crossover in the QDs at a very low pressure of 0.1 to 0.2 GPa and at about 1.2 GPa the band alignment changes over to type-II, i.e. with the electrons localized in the GaP matrix spatially separated from the holes in the InP dots [2,3]. A striking result of this work concerned the temperature behaviour of the PL intensity of the QD emission, which displayed a maximum at 70 K at 0 GPa.…”

“…From the viewpoint of fundamental research this material combination poses an interesting question about the electronic structure of the InP quantum dots (QDs) when they are embedded in pure GaP, since the latter is a strongly indirect band-gap semiconductor with the absolute minimum of the conduction band at the X point of the Brillouin zone. In fact, high-pressure photoluminescence (PL) experiments revealed that at low temperatures and ambient pressure conditions the InP/GaP dot structure exhibits type-I band alignment and that the strong optical emission arises from direct Γ -Γ optical transitions [2,3]. With increasing pressure, however, first occurs the conduction band Γ -X crossover in the QDs at a very low pressure of 0.1 to 0.2 GPa and at about 1.2 GPa the band alignment changes over to type-II, i.e.…”