Excitonic ultraviolet laser emission at room temperature from naturally made cavity in ZnO nanocrytal thin films

Kawasaki, Masashi; Ohtomo, Akira; Ohkubo, I.; Koinuma, Hideomi; Tang, Zikang; Yu, Ping; Wong, George K.; Zhang, B.P.; Segawa, Y.

doi:10.1016/s0921-5107(98)00248-7

Cited by 168 publications

(80 citation statements)

References 20 publications

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“…[1][2][3][4][5][6][7] It has higher exciton binding energy ͑60 meV for ZnO versus 28 meV for GaN͒ and higher optical gain ͑300 cm Ϫ1 ͒ than GaN ͑100 cm Ϫ1 ͒ at room temperature. 1 Moreover, recent reports on externally pumped lasing in epitaxial ZnO thin films by Kawasaki et al 2 and Bagnall et al 3 have stimulated great interest in ZnO material for realizing efficient, excitonic UV blue lasers at room temperature.…”

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confidence: 99%

Oxygen pressure-tuned epitaxy and optoelectronic properties of laser-deposited ZnO films on sapphire

Choopun

Vispute

Noch

et al. 1999

Applied Physics Letters

322

161

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Influence of oxygen pressure on the epitaxy, surface morphology, and optoelectronic properties has been studied in the case of ZnO thin films grown on sapphire (0001) by pulsed-laser deposition. Results of Rutherford backscattering and ion channeling in conjunction with atomic force microscopy clearly indicate that the growth mode, degree of epitaxy, and the defect density strongly depend on the oxygen background pressure during growth. It is also found that the growth mode and the defects strongly influence the electron mobility, free-electron concentration, and the luminescence properties of the ZnO films. By tuning the oxygen pressure during the initial and the final growth stages, smooth and epitaxial ZnO films with high optical quality, high electron mobility, and low background carrier concentration have been obtained. The implication of these results towards the fabrication of superlattices and controlled n- and p-type doping is discussed.

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confidence: 99%

Oxygen pressure-tuned epitaxy and optoelectronic properties of laser-deposited ZnO films on sapphire

Choopun

Vispute

Noch

et al. 1999

Applied Physics Letters

322

161

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“…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.…”

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confidence: 99%

“…[3][4][5][6] The origin of this behavior compared to bulk material has been attributed to giant excitonic oscillator strengths in low-dimensional nanocrystalline structures, based on theoretical studies. 3,12 Reflectance data on our samples, however, show a reduction in the oscillator strengths ͑i.e., a reduction in the longitudinal-transverse splitting, ⌬ LT ͒ compared to bulk material, in addition to increased exciton damping.…”

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confidence: 99%

“…In nanocrystalline samples, the FE population created by optical absorption in the ϳ50 nm penetration depth 18 will be strongly confined in this volume by grain boundaries. 4 In contrast, FE diffusion lengths in bulk material may be significantly larger. FE diffusion lengths at low temperature ͑Ͻ77 K͒ are reported in the range of 0.2-2 m, 16,19,20 and hence the initial exciton population will diffuse and lower its density substantially.…”

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confidence: 99%

“…There is strong evidence throughout the literature supporting this idea, showing that high intensity PL emission ͑and lasing͒ is seen from nanocrystalline ZnO thin films even when the grain structure is pronounced. 4 The mechanism of repulsion will probably be related to a variety of physical causes, but space-charge layers close to grain boundaries, associated with charge trapping at the boundaries, may be particularly important. Electric fields in these space-charge regions are known to be important in understanding the properties of ZnO thin films, and these samples in particular.…”

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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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Structures and Photoluminescence Properties of ZnO Films Epitaxially Grown by Atmospheric Pressure MOCVD

Kashiwaba

Haga

Watanabe

et al. 2002

phys. stat. sol. (b)

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High-quality ZnO (11 2 20) epitaxial films have been grown on sapphire (01 1 12) substrate by atmospheric pressure MOCVD method using zinc acetylacetonate (Zn(C 5 H 7 O 2 ) 2 ) and oxygen. The crystallinity of the ZnO films was considerably improved with increasing the film thickness. The full width at half maximum (FWHM) obtained from the w rocking curve of X-ray diffraction indicated a minimum value of 0.35 at the film thickness of 0.30 mm. The lattice constant estimated from the diffraction angle 2q was almost equivalent to the value of single crystalline bulk ZnO. The room temperature photoluminescence spectrum of the ZnO films consists of band edge emission at 380.08 nm. The low-temperature (4.2 K) photoluminescence spectrum indicates two broad lines of 3.31 and 3.32 eV from donor-acceptor pairs and one sharp line of 3.363 eV from exciton bound nature donor.

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Excitonic ultraviolet laser emission at room temperature from naturally made cavity in ZnO nanocrytal thin films

Cited by 168 publications

References 20 publications

Oxygen pressure-tuned epitaxy and optoelectronic properties of laser-deposited ZnO films on sapphire

Oxygen pressure-tuned epitaxy and optoelectronic properties of laser-deposited ZnO films on sapphire

Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

Structures and Photoluminescence Properties of ZnO Films Epitaxially Grown by Atmospheric Pressure MOCVD

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