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

Peres M, Magalhães S, Fellmann V, Daudin B, Neves AJ, Alves E, Lorenz K, Monteiro T - Nanoscale Res Lett (2011)

Bottom Line: In Eu-implanted SL structures, the GaN QD recombination was found to be dependent on the implantation fluence.Despite the fact that different deexcitation processes occur in undoped and Eu-implanted SL structures, the excitation population mechanisms were seen to be sample-independent.Two main absorption bands with maxima at approx. 4.1 and 4.7 to 4.9 eV are responsible for the population of the optically active centres in the SL samples.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Física e I3N, Universidade de Aveiro, Campus de Santiago, Aveiro, 3810-193, Portugal. tita@ua.pt.

ABSTRACT
Undoped self-assembled GaN quantum dots (QD) stacked in superlattices (SL) with AlN spacer layers were submitted to thermal annealing treatments. Changes in the balance between the quantum confinement, strain state of the stacked heterostructures and quantum confined Stark effect lead to the observation of GaN QD excitonic recombination above and below the bulk GaN bandgap. In Eu-implanted SL structures, the GaN QD recombination was found to be dependent on the implantation fluence. For samples implanted with high fluence, a broad emission band at 2.7 eV was tentatively assigned to the emission of large blurred GaN QD present in the damage region of the implanted SL. This emission band is absent in the SL structures implanted with lower fluence and hence lower defect level. In both cases, high energy emission bands at approx. 3.9 eV suggest the presence of smaller dots for which the photoluminescence intensity was seen to be constant with increasing temperatures. Despite the fact that different deexcitation processes occur in undoped and Eu-implanted SL structures, the excitation population mechanisms were seen to be sample-independent. Two main absorption bands with maxima at approx. 4.1 and 4.7 to 4.9 eV are responsible for the population of the optically active centres in the SL samples.

No MeSH data available.


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Influence of the thermal annealing on the optical (PL and PLE) and XRR properties of GaN QD/AlN SL structures. (a) Temperature-dependent PL spectra of the excitonic recombination for a 10-period GaN QD/AlN SL structure before and after thermal annealing at 1200°C (full lines). Normalised RT PLE spectra monitored at the PL band maximum for the as-grown (line + closed symbols) and annealed (line + open symbols) samples. 14 K PL and PLE spectra of an AlN layer (dashed lines). (b) Specular X-ray reflection for the as-grown and annealed GaN QD/AlN SL structures. The XRR determined period thickness is shown in the graph for both samples.
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Figure 1: Influence of the thermal annealing on the optical (PL and PLE) and XRR properties of GaN QD/AlN SL structures. (a) Temperature-dependent PL spectra of the excitonic recombination for a 10-period GaN QD/AlN SL structure before and after thermal annealing at 1200°C (full lines). Normalised RT PLE spectra monitored at the PL band maximum for the as-grown (line + closed symbols) and annealed (line + open symbols) samples. 14 K PL and PLE spectra of an AlN layer (dashed lines). (b) Specular X-ray reflection for the as-grown and annealed GaN QD/AlN SL structures. The XRR determined period thickness is shown in the graph for both samples.

Mentions: Figure 1 shows the temperature-dependent PL spectra of a 10-period as-grown and thermally annealed GaN QD/AlN SL (#1110A and #1110D, respectively). The main maxima of the GaN QD excitonic recombination occur below (before thermal annealing) and above (after thermal annealing) the bulk GaN bandgap (approx. 3.5 eV). 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. The PL thermal quenching measured between 14 K and RT is mediated by different non-radiative processes as indicated by an intensity ratio, I(14 K)/I(RT), of 4 and 2.5, respectively, for the as-grown and annealed samples, when excited with the He-Cd laser line. This ratio is usually a measure of the carrier localization on the QD and it can be concluded that a higher PL thermal stability was achieved after the thermal annealing.


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

Peres M, Magalhães S, Fellmann V, Daudin B, Neves AJ, Alves E, Lorenz K, Monteiro T - Nanoscale Res Lett (2011)

Influence of the thermal annealing on the optical (PL and PLE) and XRR properties of GaN QD/AlN SL structures. (a) Temperature-dependent PL spectra of the excitonic recombination for a 10-period GaN QD/AlN SL structure before and after thermal annealing at 1200°C (full lines). Normalised RT PLE spectra monitored at the PL band maximum for the as-grown (line + closed symbols) and annealed (line + open symbols) samples. 14 K PL and PLE spectra of an AlN layer (dashed lines). (b) Specular X-ray reflection for the as-grown and annealed GaN QD/AlN SL structures. The XRR determined period thickness is shown in the graph for both samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211471&req=5

Figure 1: Influence of the thermal annealing on the optical (PL and PLE) and XRR properties of GaN QD/AlN SL structures. (a) Temperature-dependent PL spectra of the excitonic recombination for a 10-period GaN QD/AlN SL structure before and after thermal annealing at 1200°C (full lines). Normalised RT PLE spectra monitored at the PL band maximum for the as-grown (line + closed symbols) and annealed (line + open symbols) samples. 14 K PL and PLE spectra of an AlN layer (dashed lines). (b) Specular X-ray reflection for the as-grown and annealed GaN QD/AlN SL structures. The XRR determined period thickness is shown in the graph for both samples.
Mentions: Figure 1 shows the temperature-dependent PL spectra of a 10-period as-grown and thermally annealed GaN QD/AlN SL (#1110A and #1110D, respectively). The main maxima of the GaN QD excitonic recombination occur below (before thermal annealing) and above (after thermal annealing) the bulk GaN bandgap (approx. 3.5 eV). 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. The PL thermal quenching measured between 14 K and RT is mediated by different non-radiative processes as indicated by an intensity ratio, I(14 K)/I(RT), of 4 and 2.5, respectively, for the as-grown and annealed samples, when excited with the He-Cd laser line. This ratio is usually a measure of the carrier localization on the QD and it can be concluded that a higher PL thermal stability was achieved after the thermal annealing.

Bottom Line: In Eu-implanted SL structures, the GaN QD recombination was found to be dependent on the implantation fluence.Despite the fact that different deexcitation processes occur in undoped and Eu-implanted SL structures, the excitation population mechanisms were seen to be sample-independent.Two main absorption bands with maxima at approx. 4.1 and 4.7 to 4.9 eV are responsible for the population of the optically active centres in the SL samples.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Física e I3N, Universidade de Aveiro, Campus de Santiago, Aveiro, 3810-193, Portugal. tita@ua.pt.

ABSTRACT
Undoped self-assembled GaN quantum dots (QD) stacked in superlattices (SL) with AlN spacer layers were submitted to thermal annealing treatments. Changes in the balance between the quantum confinement, strain state of the stacked heterostructures and quantum confined Stark effect lead to the observation of GaN QD excitonic recombination above and below the bulk GaN bandgap. In Eu-implanted SL structures, the GaN QD recombination was found to be dependent on the implantation fluence. For samples implanted with high fluence, a broad emission band at 2.7 eV was tentatively assigned to the emission of large blurred GaN QD present in the damage region of the implanted SL. This emission band is absent in the SL structures implanted with lower fluence and hence lower defect level. In both cases, high energy emission bands at approx. 3.9 eV suggest the presence of smaller dots for which the photoluminescence intensity was seen to be constant with increasing temperatures. Despite the fact that different deexcitation processes occur in undoped and Eu-implanted SL structures, the excitation population mechanisms were seen to be sample-independent. Two main absorption bands with maxima at approx. 4.1 and 4.7 to 4.9 eV are responsible for the population of the optically active centres in the SL samples.

No MeSH data available.


Related in: MedlinePlus