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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.


Related in: MedlinePlus

Polarization of the injected carriers. (a) Integrated PL intensity of QD emission as a function of applied voltage at 15 T. (b) Circular polarization degree of QD emission for lower and higher laser intensity as function of applied voltage at 15 T and 2 K.
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Figure 5: Polarization of the injected carriers. (a) Integrated PL intensity of QD emission as a function of applied voltage at 15 T. (b) Circular polarization degree of QD emission for lower and higher laser intensity as function of applied voltage at 15 T and 2 K.

Mentions: Figure 5a shows the voltage dependence of the integrated PL intensity of QD emission at 15T. We have observed a good correlation between the I(V) curve and integrated PL intensity for the QD emission for both circular σ+ and σ- polarizations. Figure 5b shows the bias voltage dependence of the circular polarization degree for the QD emission under low and high laser intensities at 15T. We have observed that the QD circular polarization degree is always negative and that its value depends on both the applied bias voltage and the light excitation intensity. In general, its modulus presents a maximum value near the resonant tunneling condition for photo-generated holes. For the high laser intensity condition, the polarization of the QD PL band is nearly constant (~-25%), but it shows a clear bias voltage dependence for the low laser excitation intensity. In this case, the QD polarization degree clearly becomes more negative around the hole resonance and approaches zero at the electron resonance. Those results can be correlated to the density of carriers along the RTD structure and the electron and hole g-factors at the accumulation layer. We point out two basic information that are fundamental for this analysis. First, it is expected that the g-factors of electrons and holes have opposite signs for GaAs and second, the minority carriers tend to define the effective polarization of an optical recombination. Under high laser excitation intensity, the photocreated holes become the majority carrier for the whole bias voltage range of our measurements as demonstrated by the fact that the photocurrent due to photogenerated holes is markedly larger than the electronic current in dark. Therefore, the negative polarization of the QD emission should be mainly defined by the polarization accumulated electrons for all bias voltages, which is consistent with the g-factor for electrons in GaAs. Under low excitation condition, the majority carrier should change from holes at low voltages close to the hole resonant condition (hh2 resonant peak), to electrons at high voltages, close to the electron resonant condition (e2 resonant peak). Therefore, the QD polarization should be mainly defined by electrons at low voltages and by holes at high voltages, which explains that the negative polarization of the QD emission observed at low voltages tend to reduce its modulus and become more positive at high voltages.


Spin effects in InAs self-assembled quantum dots.

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

Polarization of the injected carriers. (a) Integrated PL intensity of QD emission as a function of applied voltage at 15 T. (b) Circular polarization degree of QD emission for lower and higher laser intensity as function of applied voltage at 15 T and 2 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Polarization of the injected carriers. (a) Integrated PL intensity of QD emission as a function of applied voltage at 15 T. (b) Circular polarization degree of QD emission for lower and higher laser intensity as function of applied voltage at 15 T and 2 K.
Mentions: Figure 5a shows the voltage dependence of the integrated PL intensity of QD emission at 15T. We have observed a good correlation between the I(V) curve and integrated PL intensity for the QD emission for both circular σ+ and σ- polarizations. Figure 5b shows the bias voltage dependence of the circular polarization degree for the QD emission under low and high laser intensities at 15T. We have observed that the QD circular polarization degree is always negative and that its value depends on both the applied bias voltage and the light excitation intensity. In general, its modulus presents a maximum value near the resonant tunneling condition for photo-generated holes. For the high laser intensity condition, the polarization of the QD PL band is nearly constant (~-25%), but it shows a clear bias voltage dependence for the low laser excitation intensity. In this case, the QD polarization degree clearly becomes more negative around the hole resonance and approaches zero at the electron resonance. Those results can be correlated to the density of carriers along the RTD structure and the electron and hole g-factors at the accumulation layer. We point out two basic information that are fundamental for this analysis. First, it is expected that the g-factors of electrons and holes have opposite signs for GaAs and second, the minority carriers tend to define the effective polarization of an optical recombination. Under high laser excitation intensity, the photocreated holes become the majority carrier for the whole bias voltage range of our measurements as demonstrated by the fact that the photocurrent due to photogenerated holes is markedly larger than the electronic current in dark. Therefore, the negative polarization of the QD emission should be mainly defined by the polarization accumulated electrons for all bias voltages, which is consistent with the g-factor for electrons in GaAs. Under low excitation condition, the majority carrier should change from holes at low voltages close to the hole resonant condition (hh2 resonant peak), to electrons at high voltages, close to the electron resonant condition (e2 resonant peak). Therefore, the QD polarization should be mainly defined by electrons at low voltages and by holes at high voltages, which explains that the negative polarization of the QD emission observed at low voltages tend to reduce its modulus and become more positive at high voltages.

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