Excitonic Properties of ZnO

Klingshirn, C.; Priller, H.; Decker, Manuel; Brückner, J.; Kalt, H.; Hauschild, Robert; Zeller, Jürgen; Waag, A.; Bakin, A.; Thonke, H. Wehmann K.; Sauer, R.; Kling, Rainer; Reuß, F.; Kirchner, C.

doi:10.1007/11423256_22

Cited by 26 publications

(10 citation statements)

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“…Since ${E_{{\rm{xx}}}^{\rm{b}} }$ is larger than the splitting of the A and B VBs, in ZnO, the biexciton states which contain one hole from the A and one from the B VB or even two B holes are also observed. The binding energies of these states are similar, relative to the two involved excitons 12. 73 Biexcitons have also been observed in ZnO QWs, see, for example, ref.…”

Section: High Excitation Effectssupporting

confidence: 56%

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ZnO: Material, Physics and Applications

2007

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ZnO is presently experiencing a research boom with more than 2000 ZnO-related publications in 2005. This phenomenon is triggered, for example, by hope to use ZnO as a material for blue/UV optoelectronics as an alternative to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits that are transparent in the visible or for semiconductor spintronics. Currently, however, the main problem is to achieve high, reproducible and stable p-doping. Herein, we critically review aspects of the material growth, fundamental properties of ZnO and ZnO-based nanostructures and doping as well as present and future applications with emphasis on the electronic and optical properties including stimulated emission.

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Section: High Excitation Effectssupporting

confidence: 56%

“…But frequently, such problems tend to have an extremely long decay time. As detailed in various references,12, 44 the arguments put forward recently in favour of the normal valence‐band ordering in ZnO are not convincing. Therefore, we use in the following the inverted ordering: A Γ 7 , B Γ 9 , C Γ 7 .…”

Section: Electronic Band Structurementioning

confidence: 97%

ZnO: Material, Physics and Applications

2007

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“…Wide band gap oxide semiconductor ZnO and its related heterostructures have raised substantial interest in the optoelectronics-oriented research field in the blue/ultraviolet ͑UV͒ range. 1 Besides, with a small spin-orbit coupling and a very large exciton binding energy, ZnO represents a potential candidate for room-temperature ͑RT͒ spintronic applications. However, only few measurements on the carrier spin dynamics in bulk or even nanostructured ZnO have been published to date compared to GaAs-based structures.…”

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confidence: 99%

Exciton and hole spin dynamics in ZnO investigated by time-resolved photoluminescence experiments

et al. 2008

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The carrier spin dynamics in ZnO is investigated by time-resolved optical orientation experiments. We evidence a clear circular polarization of the donor-bound exciton luminescence in both ZnO epilayer and nonintentionally doped bulk ZnO. This allows us to measure the localized hole spin relaxation time. We find h s ϳ 350 ps at T = 1.7 K in the ZnO epilayer. The strong energy and temperature dependences of the photoluminescence polarization dynamics are well explained by the fast free exciton spin relaxation time and the ionization of bound excitons.Wide band gap oxide semiconductor ZnO and its related heterostructures have raised substantial interest in the optoelectronics-oriented research field in the blue/ultraviolet ͑UV͒ range. 1 Besides, with a small spin-orbit coupling and a very large exciton binding energy, ZnO represents a potential candidate for room-temperature ͑RT͒ spintronic applications. However, only few measurements on the carrier spin dynamics in bulk or even nanostructured ZnO have been published to date compared to GaAs-based structures. 2-4 Ghosh et al. 5 have investigated the electron spin properties in n-type ZnO structures and found an electron spin relaxation time varying from 20 ns to 190 ps when the temperature increases from T = 10 to 280 K. RT electron spin relaxation as long as 25 ns has also been measured by electron paramagnetic resonance ͑EPR͒ spectroscopy in colloidal n-doped ZnO quantum dots. 6 To the best of our knowledge, neither the exciton nor the hole spin dynamics in ZnO have been measured yet. Indeed two experimental issues arise: ͑i͒ the small value of the spinorbit coupling energy ͑9-16 meV͒ ͑Refs. 7 and 8͒ imposes resonant optical excitation conditions 9 in the near UV to create an exciton spin polarization; ͑ii͒ the direct measurement of the free hole spin relaxation by pump-probe experiments would require the fabrication of stable p-doped samples, 10,11 which remains a challenge in ZnO ͑Ref. 12͒. In order to investigate the hole spin dynamics in ZnO, we have studied the polarization properties of the exciton bound to neutral donors. Since this complex consists of a singlet of electrons and a hole, its spin polarization is directly determined by the orientation of the hole bound in the complex. [13][14][15] ZnO crystallizes in the wurtzite phase, where the hexagonal crystal field ⌬ cr and the spin-orbit coupling ⌬ so give rise to three doubly degenerated valence bands, labeled A, B, and C. The optical selection rules and oscillator strengths impose that only the transitions from the A and B valence bands are optically allowed when the light propagates along the c axis of the crystal. 7,8,13 We present in this paper a detailed investigation of the optical orientation of excitons and holes in ZnO bulk and epilayer samples. By time-resolved photoluminescence ͑PL͒ experiments, we evidence the fast free exciton spin relax-ation ͑ FX s Ͻ 10 ps͒ and we measure the hole spin relaxation time ͑up to h s ϳ 350 ps͒ in the donor-bound exciton complex.The samples under investigatio...

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“…21 Extensive studies have been performed on the optical properties of ZnO, 22,23 particularly the excitonic transition, and their potential applications. 24 In spite of continuous improvements in the techniques used, 25-31 p-type doping remains one of the most important issues to be resolved for fabrication of reliable ZnO electronic and optoelectronic devices.…”

Section: The Zno Materials Systemmentioning

confidence: 99%

Numerical Simulation of ZnO-Based Terahertz Quantum Cascade Lasers

Bellotti

Paiella

2010

Journal of Elec Materi

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In this work, a particle-based Monte Carlo model is used to quantify the potential of terahertz sources based on the ZnO-based material system relative to existing devices based on GaAs/AlGaAs quantum wells. Specifically, two otherwise identical quantum cascade structures based on ZnO/ MgZnO and GaAs/AlGaAs quantum wells are designed, and their nonequilibrium carrier distributions are then computed as a function of temperature. The simulation results show that, because of their larger optical phonon energy, ZnO/MgZnO quantum cascade laser structures exhibit weaker temperature dependence of the population inversion than in the case of similar structures made of GaAs/AlGaAs. In particular, as the temperature is increased from 10 K to 300 K, population inversion is found to decrease by a factor of 4.48 and 1.50 for the AlGaAs and MgZnO structure, respectively. Based on these results, the MgZnO devices are then predicted to be, in principle, capable of laser action without cryogenic cooling.

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Excitonic Properties of ZnO

Cited by 26 publications

References 1 publication

ZnO: Material, Physics and Applications

ZnO: Material, Physics and Applications

Exciton and hole spin dynamics in ZnO investigated by time-resolved photoluminescence experiments

Numerical Simulation of ZnO-Based Terahertz Quantum Cascade Lasers

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