Narrowing of ground energy level distribution in an array of InAs/AlAs QDs by post grown annealing

Abstract

The effect of a post growth annealing on the structure and photoluminescence (PL) of InAs/AlAs quantum dots has been studied. The annealing at temperatures below 650 ºC does not effect the PL spectrum, while a blue shift as large as 400 meV and a significant narrowing of the QD PL band are observed at annealing temperatures in the range 650-950 ºC. Transmission electron microscopy demonstrates that the changes in the PL spectrum are accompanied by an increase in the average QD size and its dispersion. The blue shift and narrowing are explained by a shift of the QD energy levels towards the level of a shallow quantum well as a result of interdiffusion.1 Introduction Self-assembled quantum dots (QDs) as objects with δ-like density of states are predicted to replace quantum wells in the active layers of optoelectronic devices such as lasers. However, the use of this QD advantage is restricted by broad distribution of the energy levels of individual QDs in QDs array. The energy dispersion is attributed to QD size, shape, composition, and strain fluctuation and manifests itself in a broadening of luminescence lines of exciton recombination in QDs. In order to decrease this dispersion growth and post growth treatment techniques were proposed. Recently, it was shown that a short-time high temperature annealing could be successfully used to decrease the width of the photoluminescence (PL) line in an array of InAs/GaAs QDs [1][2][3][4]. In this work we study effect of a high temperature annealing on photoluminescence and structure of InAs QDs embeded in an AlAs matrix. Blue shift and significant narrowing of the PL band of the QDs have observed with increase in annealing temperature as a result of shallower confining potential due to InAs-AlAs interdiffusion.

Exciton recombination dynamics in an ensemble of (In,Al)As/AlAs quantum dots with indirect band-gap and type-I band alignment

“…The largest lateral QD sizes are found for structure S4, which was annealed at the highest temperature of 800 • C. The comparison between the annealed structure S4 and the unannealed structure S2 indicates that post-growth annealing leads to an increase of the QD diameter with a broader distribution, in good agreement with previous results. 18 The annealing results in an increase of the average QD diameter from 13.8 to 19.6 nm, and S D from 60% to 75%, respectively. The diameter increase by annealing is a result of InAs diffusion from the QD into the surrounding AlAs matrix.…”

“…Nevertheless, the sharpness of the (In,Al)As/AlAs interfaces can be smeared out by means of high-temperature post-growth thermal annealing. 18 Two of the studied structures, S2 and S3, were annealed for one minute at elevated temperatures T an . Data on T an are listed in Table I, whereas technical details can be found in Ref.…”

“…The at first sight unusual reduction of the FWHM of the IQD band with increasing S D was explained in our previous study. 18 We calculated in Refs. 11, 8 the energy separation between the optical transitions of direct and indirect excitons and showed that it weakly depends on the QD size, shape, and composition.…”

“…18 The annealing results in an increase of the average QD diameter from 13.8 to 19.6 nm, and S D from 60% to 75%, respectively. The diameter increase by annealing is a result of InAs diffusion from the QD into the surrounding AlAs matrix.…”

“…Data on T an are listed in Table I, whereas technical details can be found in Ref. 18. The following, we will refer the annealed S2 structure as the S4 structure.…”