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Improved ground-state modulation characteristics in 1.3 μm InAs/GaAs quantum dot lasers by rapid thermal annealing.

Zhao H, Yoon SF, Ngo CY, Wang R - Nanoscale Res Lett (2011)

Bottom Line: The choice of annealing conditions was determined from our recently reported results.With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers.In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. zhao0097@e.ntu.edu.sg.

ABSTRACT
We investigated the ground-state (GS) modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. The choice of annealing conditions was determined from our recently reported results. With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers. In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones. The observed improvements are due to (1) the removal of defects which act as nonradiative recombination centers in the QD structure and (2) the reduction in the Auger-related recombination processes upon annealing.

No MeSH data available.


Related in: MedlinePlus

Plot of ln(I) vs. ln(Lsp1/2) for the as-grown and 600°C annealed QD devices with cavity length of 2 mm at room temperature. The Ith,GS of the as-grown and 600°C annealed QD device is 93.6 and 81.8 mA, respectively.
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Figure 7: Plot of ln(I) vs. ln(Lsp1/2) for the as-grown and 600°C annealed QD devices with cavity length of 2 mm at room temperature. The Ith,GS of the as-grown and 600°C annealed QD device is 93.6 and 81.8 mA, respectively.

Mentions: Figure 7 shows the plot of ln(I) vs. ln(Lsp1/2), where I is the injection current and Lsp is the total spontaneous emission intensity. The gradient obtained is known as the Z value. The total spontaneous emission intensity is measured by modulating the device in the unamplified region, where I < Ith. Over this limited range of I, we employed a general relationship between I and Lsp [21]: ln(I) ∝ Z ln(Lsp1/2), where 1 ≤ Z ≤ 3, depending on the relative importance of nonradiative monomolecular recombination process due to defects or impurities (Z = 1), bimolecular radiative recombination process (Z = 2) or nonradiative Auger recombination process (Z = 3). Generally, 2 ≤ Z ≤ 3 applies in InAs/GaAs QDs, especially in p-doped QDs, due to the enhanced nonradiative Auger recombination [22]. As shown in Figure 7, Z reduces from 2.748 for the as-grown device to 2.217 for the annealed device. This suggests that the radiative recombination becomes more dominant than the Auger-related recombination processes resulting from annealing [21]. It is thus reasonable to say that the radiative recombination has been enhanced after 600°C RTA. The suppression of nonradiative Auger recombination may also result in smaller carrier lifetime, thus improved high-speed modulation performances, which agrees well with our experimental results on the improved small signal modulation performances in annealed lasers (as shown in Figures 1, 3, 5). Furthermore, our experimental results also demonstrate improved quantum efficiency and reduced optical loss in the 600°C annealed lasers, which have been submitted elsewhere [9].


Improved ground-state modulation characteristics in 1.3 μm InAs/GaAs quantum dot lasers by rapid thermal annealing.

Zhao H, Yoon SF, Ngo CY, Wang R - Nanoscale Res Lett (2011)

Plot of ln(I) vs. ln(Lsp1/2) for the as-grown and 600°C annealed QD devices with cavity length of 2 mm at room temperature. The Ith,GS of the as-grown and 600°C annealed QD device is 93.6 and 81.8 mA, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211475&req=5

Figure 7: Plot of ln(I) vs. ln(Lsp1/2) for the as-grown and 600°C annealed QD devices with cavity length of 2 mm at room temperature. The Ith,GS of the as-grown and 600°C annealed QD device is 93.6 and 81.8 mA, respectively.
Mentions: Figure 7 shows the plot of ln(I) vs. ln(Lsp1/2), where I is the injection current and Lsp is the total spontaneous emission intensity. The gradient obtained is known as the Z value. The total spontaneous emission intensity is measured by modulating the device in the unamplified region, where I < Ith. Over this limited range of I, we employed a general relationship between I and Lsp [21]: ln(I) ∝ Z ln(Lsp1/2), where 1 ≤ Z ≤ 3, depending on the relative importance of nonradiative monomolecular recombination process due to defects or impurities (Z = 1), bimolecular radiative recombination process (Z = 2) or nonradiative Auger recombination process (Z = 3). Generally, 2 ≤ Z ≤ 3 applies in InAs/GaAs QDs, especially in p-doped QDs, due to the enhanced nonradiative Auger recombination [22]. As shown in Figure 7, Z reduces from 2.748 for the as-grown device to 2.217 for the annealed device. This suggests that the radiative recombination becomes more dominant than the Auger-related recombination processes resulting from annealing [21]. It is thus reasonable to say that the radiative recombination has been enhanced after 600°C RTA. The suppression of nonradiative Auger recombination may also result in smaller carrier lifetime, thus improved high-speed modulation performances, which agrees well with our experimental results on the improved small signal modulation performances in annealed lasers (as shown in Figures 1, 3, 5). Furthermore, our experimental results also demonstrate improved quantum efficiency and reduced optical loss in the 600°C annealed lasers, which have been submitted elsewhere [9].

Bottom Line: The choice of annealing conditions was determined from our recently reported results.With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers.In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. zhao0097@e.ntu.edu.sg.

ABSTRACT
We investigated the ground-state (GS) modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. The choice of annealing conditions was determined from our recently reported results. With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers. In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones. The observed improvements are due to (1) the removal of defects which act as nonradiative recombination centers in the QD structure and (2) the reduction in the Auger-related recombination processes upon annealing.

No MeSH data available.


Related in: MedlinePlus