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Spin effects in InAs self-assembled quantum dots.

Dos Santos EC, Gobato YG, Brasil MJ, Taylor DA, Henini M - Nanoscale Res Lett (2011)

Bottom Line: We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW).We have observed that the QD circular polarization degree depends on applied voltage and light intensity.Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, Federal University of São Carlos, São Carlos, Brazil. yara@df.ufscar.br.

ABSTRACT
We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW). We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

No MeSH data available.


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Current-voltage characteristic curves. (a) in dark and (b) for several laser intensities.
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Figure 2: Current-voltage characteristic curves. (a) in dark and (b) for several laser intensities.

Mentions: Figure 2 shows the I(V) characteristic curves for several laser intensities. In dark condition, we have observed only one electron resonant peak which was associated to the resonant tunneling through the second confined level e2 in the QW. It was shown previously [8] that even when QDs are formed, a wetting layer is still present and changes the position of the first QW confined level (e1) to a new position below the GaAs conduction-band. Therefore, resonant tunneling through e1 states cannot be observed in the I(V) characteristics curve. Under light excitation, holes are photocreated in contact layer region and tunnel through the double barrier structure. An additional resonant peak associated to hh2 hole resonance [8] is observed in lower voltage region under higher laser intensities. We have also observed that the photocurrent rapidly increases at low voltages (0.2 V), saturates in the region of about 0.2 and 0.4 V, and eventually follows the similar resonant voltage dependence as the current measured in dark conditions. We point out that even at zero bias, the QDs states which have a lower energy than the GaAs contacts, should be filled with electrons from the contact layers, resulting in a negative charge accumulation in the QW region. The potential profile of our structure should then be changed with respect to a reference sample without quantum dots [8,9]. In this case, an asymmetry in the impurity concentration of the contact layers should result in a non-zero electric field at the quantum well and, thus, in a non-zero current, at zero bias. We have indeed observed that the crossing of the I(V) curves under light excitation occurs at a voltage slightly larger than zero, which indicates that there is a small asymmetry in the impurity concentrations of the doped contact-layers. The crossing voltage corresponds to the flat band condition of the RTD structure with QDs.


Spin effects in InAs self-assembled quantum dots.

Dos Santos EC, Gobato YG, Brasil MJ, Taylor DA, Henini M - Nanoscale Res Lett (2011)

Current-voltage characteristic curves. (a) in dark and (b) for several laser intensities.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211160&req=5

Figure 2: Current-voltage characteristic curves. (a) in dark and (b) for several laser intensities.
Mentions: Figure 2 shows the I(V) characteristic curves for several laser intensities. In dark condition, we have observed only one electron resonant peak which was associated to the resonant tunneling through the second confined level e2 in the QW. It was shown previously [8] that even when QDs are formed, a wetting layer is still present and changes the position of the first QW confined level (e1) to a new position below the GaAs conduction-band. Therefore, resonant tunneling through e1 states cannot be observed in the I(V) characteristics curve. Under light excitation, holes are photocreated in contact layer region and tunnel through the double barrier structure. An additional resonant peak associated to hh2 hole resonance [8] is observed in lower voltage region under higher laser intensities. We have also observed that the photocurrent rapidly increases at low voltages (0.2 V), saturates in the region of about 0.2 and 0.4 V, and eventually follows the similar resonant voltage dependence as the current measured in dark conditions. We point out that even at zero bias, the QDs states which have a lower energy than the GaAs contacts, should be filled with electrons from the contact layers, resulting in a negative charge accumulation in the QW region. The potential profile of our structure should then be changed with respect to a reference sample without quantum dots [8,9]. In this case, an asymmetry in the impurity concentration of the contact layers should result in a non-zero electric field at the quantum well and, thus, in a non-zero current, at zero bias. We have indeed observed that the crossing of the I(V) curves under light excitation occurs at a voltage slightly larger than zero, which indicates that there is a small asymmetry in the impurity concentrations of the doped contact-layers. The crossing voltage corresponds to the flat band condition of the RTD structure with QDs.

Bottom Line: We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW).We have observed that the QD circular polarization degree depends on applied voltage and light intensity.Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, Federal University of São Carlos, São Carlos, Brazil. yara@df.ufscar.br.

ABSTRACT
We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW). We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

No MeSH data available.


Related in: MedlinePlus