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Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands.

Das S, Das K, Singha RK, Manna S, Dhar A, Ray SK, Raychaudhuri AK - Nanoscale Res Lett (2011)

Bottom Line: The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy.The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands.The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. physkr@phy.iitkgp.ernet.in.

ABSTRACT
The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail.

No MeSH data available.


Related in: MedlinePlus

Temperature-dependent PL from Ge islands grown on (a) unpatterned substrate and (b) patterned substrate (500-nm pitch).
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Figure 4: Temperature-dependent PL from Ge islands grown on (a) unpatterned substrate and (b) patterned substrate (500-nm pitch).

Mentions: Figure 4a,b shows the temperature-dependent PL spectra of Ge islands grown on unpatterned and patterned substrates (500-nm pitch sample), respectively. No appreciable PL intensity enhancement was observed for sample with 160-nm pitch over that of unpatterned sample. At a particular temperature (30 K), the PL emission intensity from the highly ordered island (500-nm pitch sample) is one order of magnitude higher than the randomly distributed islands. The details of different PL peak positions and their origins are summarized in Table 1. PL spectra (30 K) from the unpatterned substrate consist of three major peaks at 0.761, 0.702, and 0.665 eV. From Figure 1b, it is clear that islands distribution is nearly bimodal in unpatterned area. The smaller islands have average height approx. 7 nm, whereas the larger ones are approx. 18 nm in height. The observed broad PL peak around 0.761 eV is attributed to the no-phonon (NP) transition of charge carriers localized in and around the smaller islands. Owing to a type-II band alignment, the holes are trapped inside the islands, while the electrons are weakly localized in the strained Si layers around the islands [3]. An asymmetry in the lower energy side of this 0.761 eV peak reveals the existence of TO phonon-assisted transition along with the NP one. The ratio of NP/TO phonon peak intensity is larger in smaller islands because of higher spatial confinement, which leads to the breaking of k-selection rule. The other two peaks located at 0.702 and 0.665 eV, respectively, are identified as the NP and TO phonon lines of larger-sized islands. The separation between NP and TO lines is 37 meV, which is close to the energy of the characteristic Ge-Ge phonons [17]. The energy difference between the NP peaks of smaller and larger islands is about 59 meV. This can be explained by higher confinement energy for smaller islands as PL energy is given by(1)


Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands.

Das S, Das K, Singha RK, Manna S, Dhar A, Ray SK, Raychaudhuri AK - Nanoscale Res Lett (2011)

Temperature-dependent PL from Ge islands grown on (a) unpatterned substrate and (b) patterned substrate (500-nm pitch).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211512&req=5

Figure 4: Temperature-dependent PL from Ge islands grown on (a) unpatterned substrate and (b) patterned substrate (500-nm pitch).
Mentions: Figure 4a,b shows the temperature-dependent PL spectra of Ge islands grown on unpatterned and patterned substrates (500-nm pitch sample), respectively. No appreciable PL intensity enhancement was observed for sample with 160-nm pitch over that of unpatterned sample. At a particular temperature (30 K), the PL emission intensity from the highly ordered island (500-nm pitch sample) is one order of magnitude higher than the randomly distributed islands. The details of different PL peak positions and their origins are summarized in Table 1. PL spectra (30 K) from the unpatterned substrate consist of three major peaks at 0.761, 0.702, and 0.665 eV. From Figure 1b, it is clear that islands distribution is nearly bimodal in unpatterned area. The smaller islands have average height approx. 7 nm, whereas the larger ones are approx. 18 nm in height. The observed broad PL peak around 0.761 eV is attributed to the no-phonon (NP) transition of charge carriers localized in and around the smaller islands. Owing to a type-II band alignment, the holes are trapped inside the islands, while the electrons are weakly localized in the strained Si layers around the islands [3]. An asymmetry in the lower energy side of this 0.761 eV peak reveals the existence of TO phonon-assisted transition along with the NP one. The ratio of NP/TO phonon peak intensity is larger in smaller islands because of higher spatial confinement, which leads to the breaking of k-selection rule. The other two peaks located at 0.702 and 0.665 eV, respectively, are identified as the NP and TO phonon lines of larger-sized islands. The separation between NP and TO lines is 37 meV, which is close to the energy of the characteristic Ge-Ge phonons [17]. The energy difference between the NP peaks of smaller and larger islands is about 59 meV. This can be explained by higher confinement energy for smaller islands as PL energy is given by(1)

Bottom Line: The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy.The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands.The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. physkr@phy.iitkgp.ernet.in.

ABSTRACT
The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail.

No MeSH data available.


Related in: MedlinePlus