Influence of thermal annealing on the structural and optical properties of GaN/AlN quantum dots

Abstract

The influence of the post-growth thermal annealing on the structural and optical properties of GaN/AlN quantum dots (QDs) is reported. X-ray techniques suggest smooth and high quality interfaces of the stacked multilayer structures for the asgrown and annealed samples without any period thickness change. High-angle annular dark field images by scanning transmission electron microscopy show an intermixing between the GaN QDs and AlN spacers after annealing. The QDs recombination shifts to lower energies (red shift) for big dots and to higher energies (blue shift) for small dots, reflecting two competitive processes taking place during the thermal annealing.

Functionalizing self-assembled GaN quantum dot superlattices by Eu-implantation

“…X-ray reflection ͑XRR͒ profiles of the as-grown samples have been published previously; 19 the derived period thickness for both samples discussed here is 9.5͑2͒ nm and does not change with implantation or annealing. The high number of visible SL peaks in XRR specular curves 19 and XRD 2 − scans ͑up to order 6, see Fig.…”

“…The high number of visible SL peaks in XRR specular curves 19 and XRD 2 − scans ͑up to order 6, see Fig. 2͒ reveal an excellent quality of layers and interfaces.…”

“…Besides the Eu 3+ emission all SL samples also maintain their excitonic QD emission ͑not shown͒ at ϳ450 nm which is slightly blueshifted compared to the as-grown sample consistent with an earlier study of annealed QDs. 19 For the two higher implantation fluences, in the ionimplanted and annealed SL, the peak position of the 5 D 0 → 7 F 2 transition occurs around 624 nm. Three sharp but partially overlapping lines can be distinguished and a direct comparison with the spectrum of the AlN:Eu layer indicates that the Eu 3+ emission in the SL samples implanted with 1 ϫ 10 14 and 1 ϫ 10 15 cm −2 arises mainly from the AlN host ͑buffer, spacer or capping layers͒.…”

“…19 The symmetric 2 − scans discussed so far only give information on the c-lattice parameter. In order to investigate if the implantation also affects the average a-lattice parameter of the SL, RSMs around the 105 asymmetric reciprocal lattice point were acquired for sample no.…”

Effect of Eu-implantation and annealing on the GaN quantum dots excitonic recombination

“…This suggests that the annealing of the SL structure at 1200°C in nitrogen promotes a change in the balance between the QC and QCSE as seen by the high-energy shift of the GaN QD recombination [ 7 ]. Among the various effects which could be responsible for the blue shift of the PL peak position, both interdiffusion and thermally-induced strain relaxation mechanism should be considered to explain the competition between the QC and QCSE [ 7 ]. The large number of satellites observed by XRR (Figure 1b ) indicates that both the as-grown and the annealed SL have smooth interfaces and high-crystalline quality.…”