Photoluminescence up-conversion in InAs/GaAs self-assembled quantum dots

Abstract

We report up-converted photoluminescence in a structure with InAs quantum dots embedded in GaAs. An efficient emission from the GaAs barrier is observed with resonant excitation of both the dots and the wetting layer. The intensity of the up-converted luminescence is found to increase superlinearly with the excitation density. The results suggest that the observed effect is due to a two-step two-photon absorption process involving quantum dot states.Photoluminescence ͑PL͒ up-conversion in semiconductor heterojunctions ͑HJs͒ and quantum wells ͑QWs͒, i.e., the observation of an emission at energies higher than that of the excitation energy, has attracted much attention in the last few years. 1-8 Up-conversion is a well-known phenomenon in nonlinear optics, but processes like second-harmonic generation and two-photon absorption ͑TPA͒ occur primary at high excitation intensities ͑уkW/cm 2 ͒ and are usually quite inefficient in continuous-wave ͑cw͒ experiments. 9 On the other hand, a highly efficient PL up-conversion at extremely low excitation intensity ͑0.1-10 W/cm 2 ͒ has been observed in semiconductor heterostructures. [1][2][3][4][5][6][7][8] In these experiments, the carriers photoexcited in the narrow gap material are redistributed into the wide gap material where they undergo recombination and give rise to an up-converted PL ͑UPL͒. For the mechanisms that up convert the carriers, Auger process 1-3 and two-step, two-photon absorption ͑TS-TPA͒ have been suggested. [4][5][6][7][8] In the Auger process, the energy released by the electron-hole recombination is transferred to another electron or hole. The excited carriers are ejected into the barrier and after relaxation to the band edges they recombine radiatively to give UPL. The presence of a heteroboundary lifts the k-conservation requirement in the direction perpendicular to the interface and allows Auger recombination without a thermal threshold. On the other hand, the TS-TPA must be distinguished from the purely TPA in nonlinear optics, because the intermediate state is real and relaxation of the excitation to lower-lying real states may occur before the second photon is absorbed. The up-converted band-to-band luminescence has also been previously observed in bulk semiconductors. 10,11 The effect has been explained by a TS-TPA process involving a deep energy level as an intermediate state. Recently, PL up-conversion has been reported for InP/GaInP self-assembled quantum dots ͑QDs͒ 12 and InP and CdSe colloidal QDs. 13 In Ref. 12, QD emission in the presence of electrical current flowing through the sample has been observed with an optical excitation below the ground state. The electrical current provides electrons, some of which are trapped into the QDs, while the holes are optically excited via deep energy levels localized close to the QDs. In the case of colloidal QDs, the PL up-conversion has been explained by a microscopic mechanism that involves the surface states near the valence band and conduction band edges. 13 Here we report on PL up-conversion in ...

Decoherence processes during optical manipulation of excitonic qubits in semiconductor quantum dots

“…Finally we note that we also considered processes such as two-photon absorption, presumed to be responsible for the up-converted PL at the band-edge under strong excitation [24]. Theoretical estimates of the resulting scattering rate for an exciton in an excited state come short by several orders of magnitude and would not significantly affect the dephasing process.…”

Optical and Dynamic Properties of Undoped and Doped Semiconductor Nanostructures

“…Long-lived intermediate states have been suggested to be essential for luminescence up-conversion in some heterostructures such as GaAs/Al x Ga 1-x As [136]. For semiconductor nanoparticles or quantum dots with confinement in three dimensions, luminescence up-conversion has only recently been reported for CdS [145], InP [126,146], CdSe [126], InAs/GaAs [147], and Er 3+ -doped BaTiO 3 [148]. Surface states have been proposed to play an important role in the up-conversion in nanoparticles such as InP and CdSe [126].…”

Efficient upconversion of photoluminescence via two-photon absorption in bulk and nanorod ZnO

“…Strictly speaking, a quadratic dependence of the UPL intensity on W ex may be expected for such process. However, the exact value of the power factor is known to decrease [16][17][18][19] As to a possible origin of the defect/impurity level involved in the TS-TPA, it is most likely related to an intrinsic defect or a residual impurity due to contaminant, or their complex, as all investigated structures were intentionally undoped. Common trace impurities 7 in ZnO that introduce deep levels within the bandgap include Cu, Li, Mn and Pb [23,23].…”

“…impurity/defect levels. Such two-step two-photon-absorption (TS-TPA) has previously been reported in a number of semiconductor materials [16][17][18][19] and exhibits a weaker dependence on the excitation intensity (with a power factor ≤ 2). The TS-TPA has most recently been reported in ZnO microcrystals [12], though the energy position and origin of the involved defects remain questionable.…”