Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots

Abstract

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.

InAs quantum dot morphology after capping with In, N, Sb alloyed thin films

“…This is in agreement with results from scanning transmission electron microscopy studies on similar samples. 22 Since the accumulation of Sb on top of the QDs is not observed with GaAsSb capping (layer 1), it must be due to the concomitant presence of N and Sb. Despite the lower growth temperature, the quaternary alloy reorganizes itself, likely to minimize strain, giving rise to a final complex configuration.…”

Effect of annealing in the Sb and In distribution of type II GaAsSb-capped InAs quantum dots

“…Indeed, the average Sb content in the SRL was estimated assuming the validity of Vegard's law at these contents by using the same procedure described in [29]. Taking all in account, these results imply a similar peak Sb content in both samples, about (20 ±1)%, that is quite far from the nominal value of 28%.…”

“…The inset shows the resolved cation and anion columns. The second and third rows show maps of normalized anion and cation intensity [28,29]. the more usual situation, where In is confined in the QDs; and a second, where there is a small accumulation of In over the QDs.…”

Long-wavelength room-temperature luminescence from InAs/GaAs quantum dots with an optimized GaAsSbN capping layer

“…This could be related to a reduced composition modulation that resulted from a lower diffusion of N and Sb atoms on the growth surface. In particular, the reduced FWHM of the PL seems to indicate a homogenization of the CL composition on top of the QDs, where a strong Sb accumulation induced by the presence of N was reported when growing at 1 ML s −1 [14]. Moreover, the shorter time of exposure to the plasma could be attenuating the damage induced by the excited N species, mainly N ions, coming from the plasma source.…”

“…However, significant structural changes of the capping layer due to the addition of N have been found to take place [14]. Strain and compositional inhomogeneities are induced during the CL growth, yielding a degradation of the luminescence such that, as far as we know, no room-temperature (RT) emission has been reported to date using such a CL.…”