Spatially direct and indirect transitions observed for Si/Ge quantum dots

Larsson, Mats; Elfving, Anders; Holtz, Per-Olof; Hansson, G. V.; Ni, Wei‐Xin

doi:10.1063/1.1587259

Cited by 45 publications

(27 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Exciting with a laser power of 10 mW, there is a gradual transition from a predominant low energy band to a dominating high energy band with increasing temperature. The temperature dependence consequently supports the interpretation given above where the low emission band is ascribed to the spatially indirect recombination and the high energy band is attributed to the spatially direct transitions ͑also discussed in our previous work 23 ͒. Raising the sample temperature in- creases the probability for the electrons to populate the higher energy level inside the Ge dot, which opens the possibility for the spatially direct transition.…”

Section: Temperature and Excitation Power Dependence Of Plsupporting

confidence: 71%

Growth-temperature-dependent band alignment inSi∕Gequantum dots from photoluminescence spectroscopy

Larsson

Elfving

et al. 2006

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

The present work is a photoluminescence study of Si-embedded Stranski-Krastanov Ge quantum dots. The value of the conduction band offset is a result of the magnitude of the tensile strain in the Si surrounding the compressive strained Ge dot. Due to the increased Si/ Ge intermixing and reduced strain in the Si barrier, a reduction of the conduction band offset is observed at increased growth temperatures. The optical properties as derived from photoluminescence spectroscopy are correlated with structural properties obtained as a function of the growth temperature. High growth temperatures result in large Ge dots with low density due to the pronounced surface diffusion and Si/ Ge intermixing. As confirmed by photoluminescence, the band gap of the Ge dots increases with increased growth temperature due to the higher degree of Si/ Ge intermixing. The band alignment is of type II in these structures, but the occurrence of both spatially indirect and spatially direct transitions are confirmed in temperature-dependent photoluminescence measurements with varied excitation power conditions. An increasing temperature results in a gradual transition from the spatially indirect to the spatially direct recombination in the type-II band lineup, due to higher oscillator strength for the spatially direct transition combined with a higher population factor at higher temperatures.

show abstract

Section: Temperature and Excitation Power Dependence Of Plsupporting

confidence: 71%

Growth-temperature-dependent band alignment inSi∕Gequantum dots from photoluminescence spectroscopy

Larsson

Elfving

et al. 2006

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

show abstract

“…Although Ge is also a semiconductor with indirect band gap, one of the promising approaches to increase the luminescence efficiency is to use Ge/Si nanostructures like quantum wells and Ge self-assembled quantum dots (QDs). In such QDs, the selection rules can be relaxed due to the three-dimensional carrier localization and therefore the emission efficiency can be enhanced [2]- [4]. Moreover, it is easy to grow high-quality Ge QDs directly on Si wafer.…”

Section: Introductionmentioning

confidence: 99%

(Invited) Electroluminescence from Micro-Cavities of Photonic Crystals, Micro-Disks and Rings Including Ge Dots Formed on SOI Substrates

Shiraki

Xia

et al. 2012

ECS Trans.

View full text Add to dashboard Cite

We fabricated Si micro-cavities with Ge dots and successfully observed electroluminescence at room temperature. In the case of micro-disks, we observed both modes of whispering gallery modes and Fabry-Perot modes in photoluminescence, but the latter was found to be well eliminated from micro-rings. For photonic crystals, we observed systematic dependence of PL peaks on the structure parameters such as the diameter and period of air holes and crystal pattern. More than one thousand of Q-factor was observed in these photonic crystals. Well resolved electroluminescence peaks were observed both for micro-disks and photonic crystals at room temperature. However, the line width was found to be much broader than that of PL samples, probably due to the additional metal electrodes, oxide films and doping regions which are not included in PL samples. Moreover, the peak shift to higher energies coming from thermal treatment for diode fabrication was observed.

show abstract

“…On the other hand, the optical analysis of any SAQDs is usually performed using embedded dots, since the surface states act as efficient non-radiative channels for uncapped dots. Previous studies using uncapped SAQDs have indeed observed weaker photoluminescence ͑PL͒ as compared to capped dots on systems such as InAs/GaAs, 6 InGaAs/GaAs, 7 Ge/Si, 8 and InP/InGaP. 9 In contrast, uncapped InP/GaAs SAQDs present an efficient PL emission that allows us to obtain structural and optical properties from the same sample, which is actually a very important advantage when investigating SAQD properties.…”

Section: Introductionmentioning

confidence: 99%

Structural and optical properties of InP quantum dots grown on GaAs (001)

Godoy

Nakaema

Lopes

et al. 2007

Phys. Status Solidi (c)

View full text Add to dashboard Cite

We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots.

show abstract

Spatially direct and indirect transitions observed for Si/Ge quantum dots

Cited by 45 publications

References 9 publications

Growth-temperature-dependent band alignment inSi∕Gequantum dots from photoluminescence spectroscopy

Growth-temperature-dependent band alignment inSi∕Gequantum dots from photoluminescence spectroscopy

(Invited) Electroluminescence from Micro-Cavities of Photonic Crystals, Micro-Disks and Rings Including Ge Dots Formed on SOI Substrates

Structural and optical properties of InP quantum dots grown on GaAs (001)

Contact Info

Product

Resources

About