The Luminescence of ZnO under High One‐ and Two‐Quantum Excitation

Klingshirn, C.

doi:10.1002/pssb.2220710216

Cited by 595 publications

(269 citation statements)

References 24 publications

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“…Still, the LDA+U band gaps, e.g. 1.53 eV in ZnO and ~0 eV in CuInSe 2 are much smaller than the experimental gaps (3.37 eV in ZnO [41] and 1.04 eV in CuInSe 2 [42]). The remaining discrepancy is accommodated by shifting the CBM upwards (by ∆E C ).…”

Section: Methods Of Calculationmentioning

confidence: 97%

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

2005

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Using first-principles electronic structure calculations we identify the anion vacancies in II-VI and chalcopyrite Cu-III-VI 2 semiconductors as a class of intrinsic defects that can exhibit metastable behavior. Specifically, we predict persistent electron photoconductivity (n-type PPC) caused by the oxygen vacancy V O in n-ZnO, and persistent hole photoconductivity (p-type PPC) caused by the Se vacancy V Se in p-CuInSe 2 and p-CuGaSe 2 . We find that V Se in the chalcopyrite materials is amphoteric having two "negative-U" like transitions, i.e. a double-donor transition ε(2+/0) close to the valence band and a double-acceptor transition ε(0/2−) closer to the conduction band. We introduce a classification scheme that distinguishes two types of defects (e.g., donors): type-α, which have a defect-localized-state (DLS) in the gap, and type-β, which have a resonant DLS within the host bands (e.g., conduction band). In the latter case, the introduced carriers (e.g., electrons) relax to the band edge where they can occupy a perturbedhost-state (PHS). Type α is non-conducting, whereas type β is conducting. We identify the neutral anion vacancy as type-α and the doubly positively charged vacancy as type-β. We suggest that illumination changes the charge state of the anion vacancy and leads to a crossover between α-and β-type behavior, resulting in metastability and PPC. In CuInSe 2 , the metastable behavior of V Se is carried over to the (V Se -V Cu ) complex, which we identify as the physical origin of PPC observed experimentally. We explain previous puzzling experimental results in ZnO and CuInSe 2 in the light of this model.

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Section: Methods Of Calculationmentioning

confidence: 97%

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

2005

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“…It has recently become the focus of many studies, since a wide range of applications are possible due to its direct and large bandgap [2]. Devices such as detectors, lasers and diodes operating in the blue and ultraviolet (UV) spectrum have been reported [3], but are not very efficient yet.…”

Section: Introductionmentioning

confidence: 99%

Electronic properties of defects in pulsed-laser deposition grown ZnO with levels at 300 and 370meV below the conduction band

Auret

Meyer

Rensburg

et al. 2007

Physica B: Condensed Matter

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We have used deep level transient spectroscopy (DLTS) to characterize defects in ZnO grown by pulsed-laser deposition (PLD). Using high resolution Laplace DLTS, we found that at the high temperature side of the commonly observed defect E3 (about 300 meV below the conduction band) another close lying peak (E3′ with thermal activation energy of 370 meV) is also observed. The concentration ratio of E3 and E3′ depends on the annealing history of the samples. It is most prevalent in as-grown samples and samples that had been annealed in an oxygen atmosphere. This suggests that E3′ may be related to the incorporation of oxygen in the lattice. Electron capture onto that E3′ defect strongly increases with increasing temperature.

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“…With increasing excitation, one observes the growth first of the FE band at 3.33 eV and then the P band at 3.23 eV, corresponding to the well-known exciton-exciton collision process, ϳ100 meV below the FE. 2 The emission bands are significantly broadened due to the damping effects mentioned earlier. The plot of integrated emission intensity versus excitation power shown in Fig.…”

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confidence: 87%

Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

Tobin

McGlynn

Henry

et al. 2006

Applied Physics Letters

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We present optically pumped emission data for ZnO, showing that high excitation effects and stimulated emission/lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading-via the nonlinear dependence of emission in the exciton bands on the pump intensity-to large increases in emission and to stimulated emission. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2174107͔ ZnO has recently emerged as a strong candidate for ultraviolet photonic devices, with attractive properties, including a large exciton binding energy of 60 meV enabling efficient excitonic emission at room temperature. Many groups have studied stimulated emission and lasing properties of bulk ZnO, under electron beam 1 and optical pumping, 2 but evidence for stimulated emission and lasing has only been seen at rather low temperatures. Recent studies of optically pumped nanocrystalline samples reveal stimulated emission and lasing even at room temperature, in contrast to the bulk studies, even in samples of similar or inferior quality compared to bulk crystals. [3][4][5][6] We have studied optically pumped emission at room temperature from bulk single-crystal material ͑Eagle-Picher Corporation͒ and samples grown by pulsed laser deposition ͑PLD͒ on c sapphire. Details of the sample growth are given elsewhere. 7 Some films were annealed in O 2 ͑0.3 mbar͒ between 400°C and 600°C in the growth chamber after deposition leading to a consistent increase in grain size ͑30 → 80 nm͒ with annealing temperature. 7 All films show evidence of electric-field damping of the free exciton ͑FE͒ and film thicknesses are in the range of 200-250 nm. 7,8 The samples were studied using continuous-wave photoluminescence ͑PL͒ and high excitation pumping with a frequencytripled Nd:YAG laser ͑355 nm 10 Hz 6 ns pulse width͒ focused on the sample to a diameter of ϳ1.2 mm ͑determined by the knife-edge method͒ enabling excitation intensities in the range of 500-7000 kW/ cm 2 . Full details are described in Refs. 7 and 9. Figure 1͑a͒ shows emission at 300 K from a PLD sample ͑annealed at 500°C͒ as a function of increasing Nd:YAG excitation power. The data from this sample are representative of all the PLD samples. With increasing excitation, one observes the growth first of the FE band at 3.33 eV and then the P band at 3.23 eV, corresponding to the well-known exciton-exciton collision process, ϳ100 meV below the FE. 2 The emission bands are significantly broadened due to the damping effects mentioned earlier. The plot of integrated emission intensity versus excitation power shown in Fig. 1͑b͒ exhibits a distinct threshold at a pump power slightly above 2000 kW/ cm 2 , which is not explained by a superlinear power-law dependence of emis...

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The Luminescence of ZnO under High One‐ and Two‐Quantum Excitation

Cited by 595 publications

References 24 publications

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

Electronic properties of defects in pulsed-laser deposition grown ZnO with levels at 300 and 370meV below the conduction band

Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

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