Time-resolved photoluminescence in ZnO epitaxial thin films studied by up-conversion method

Yamamoto, Akio; Kido, Takeo; Goto, T.; Chen, Yefan; Yao, Takafumi; Kasuya, A.

doi:10.1016/s0022-0248(00)00098-1

Cited by 38 publications

(28 citation statements)

References 11 publications

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“…At the recovery stage, the intensity of the EHP band therefore decreases with time, and consequently the EHP band continuously converts to the P band after several picoseconds through a reverse Mott transition. Although the bandgap renormalization and the cooling of the carriers in the EHP state were also observed in previous pump-probe and up-conversion experiments [3,4], dynamics of the EHP was not fully clarified. Since the time-resolved luminescence spectra can be directly observed in the OKG method, the whole dynamics of the EHP including the conversion into a high density excitonic state was studied for the first time in this experiment.…”

Section: Resultsmentioning

confidence: 90%

“…Recently, stimulated emission and room temperature lasing from an exciton-exciton collision process and an electron-hole plasma (EHP) with a low threshold was observed in ZnO epitaxial thin films [1,2]. Dynamics of such high density states in ZnO epilayers was also studied by pump-probe transient absorption spectroscopy [3], up-conversion technique [4] and optical Kerr gate (OKG) method [5]. The OKG method is considered to be the most powerful method to clarify dynamics of the high density carriers, because time-resolved luminescence spectra are directly observed in femtosecond time regime [5,6].…”

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confidence: 99%

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Conversion of an electron–hole plasma into a high density excitonic state in ZnO epitaxial thin films

Toshine

Takeda

et al. 2004

phys. stat. sol. (c)

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PACS 78.47.+p, 78.55.Et Time-resolved luminescence spectra of an exciton-exciton scattering process and an electron-hole plasma (EHP) were measured in ZnO epitaxial thin films by the optical Kerr gate method. At moderate excitation density below critical Mott density, stimulated emission of luminescence due to the exciton-exciton scattering process (P band) was observed. The P band shows a red shift and spectral narrowing in the first 1-2 ps after the excitation which reflects a thermal redistribution of excitons in the n = 1 excitonic state. On the other hand, at high excitation density above the critical Mott density, stimulated emission of the luminescence due to the EHP was observed. After thermalization of the EHP, the luminescence intensity of the EHP band decreases with time, and the EHP band converts to the P band after ~10 ps through a reverse Mott transition. 1 Introduction ZnO-based II-VI semiconductors have attracted much interest because of their suitable properties for short wavelength optoelectronic applications. Compared with the other wide gap materials, ZnO has larger exciton binding energy (~60 meV), which assures more efficient excitonic emission at higher temperatures. Recently, stimulated emission and room temperature lasing from an exciton-exciton collision process and an electron-hole plasma (EHP) with a low threshold was observed in ZnO epitaxial thin films [1,2]. Dynamics of such high density states in ZnO epilayers was also studied by pump-probe transient absorption spectroscopy [3], up-conversion technique [4] and optical Kerr gate (OKG) method [5]. The OKG method is considered to be the most powerful method to clarify dynamics of the high density carriers, because time-resolved luminescence spectra are directly observed in femtosecond time regime [5,6]. Here, we report on dynamical behavior of the EHP and an exciton-exciton scattering process and conversion of EHP to high density excitonic state in ZnO epitaxial thin films studied by the OKG method.

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Section: Resultsmentioning

confidence: 90%

mentioning

confidence: 99%

Conversion of an electron–hole plasma into a high density excitonic state in ZnO epitaxial thin films

Toshine

Takeda

et al. 2004

phys. stat. sol. (c)

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“…7-11 Therefore, before higher quality ZnO thin films of n-type and p-type conductivities can be fabricated, it is important to further clarify the role of intrinsic defects on the dynamics of carriers/excitons trapping and recombination in the material from the viewpoints of basic physics as well as devices engineering. Moreover, much less is known about relaxation mechanisms of high-density carriers/excitions in ZnO epilayers, [12][13][14][15] which is of particular importance when related to high-injection devices. For probing the picture of carrier dynamics in semiconductors, one popular technique is the ultrafast laser based all optical pump-probe differential reflectivity(PPR) spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Intensity-dependent dynamics of photoexcited carriers in ZnO epilayers studied using pump-probe reflectance

Guo

et al. 2005

SPIE Proceedings

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The dynamics of carriers/excitons in as grown and annealed ZnO epilayers at room-temperature under high excitation densities were monitored by pump-probe(4.65/3.1 eV) differential reflectance R ∆ transients on a time scale equal to 100 ps. The R ∆ buildup showed a density-independent time delay of about 1.45 ps relative to the pump pulse, indicative of hot phonon effects, i.e., LO-phonon bottleneck, common to the as grown and annealed ZnO epilayers. Both appeared an initial fast R ∆ decay with a time constant of about 20-25 ps due to rapid defect trapping. After the fast decay, the R ∆ transient of the as grown ZnO became of sign reversal and turned to an induced absorption signal from defect levels with a decay time of several hundred picoseconds weakly dependent on excitation intensities. For the annealed ZnO, no change over in sign was observed on the slowly recovering component of R ∆ , of which, in particular, the decay time was found to linearly depend upon carrier density. This finding, as confirmed by photoluminescence measurements, was attributed to a bimolecular recombination in terms of an exciton-exciton scattering in ZnO. These observations suggest that this unique pump-probe technique can provide a useful tool for understanding the defect physics of semiconducting materials.

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“…Meanwhile, the investigation and understanding of the dynamic processes of fundamental optical transitions in ZnO thin films are just in their infancy. 5,[10][11][12][13][14][15] In this regard, time-resolved PL(TRPL) can provide a nondestructive and powerful technique for studying ZnO thin films, because of which the temporal information combined with spectral PL data can elucidate the dynamics of carriers involved in optical transitions. The exciton lifetime, an important quantity related to material quality and device performance, can be measured by TRPL.…”

Section: Introductionmentioning

confidence: 99%

Time-integrated and time-resolved photoluminescence in ZnO epitaxial thin films grown onto (100) silicon substrates by MOCVD

Guo

Hong

et al. 2005

SPIE Proceedings

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Room-temperature spectral and temporal behaviors of UV and visible emissions in ZnO epilayers grown onto (100) silicon substrates have been investigated by means of time-integrated and time-resolved photoluminescence(TIPL & TRPL). The PL lifetimes as short as 25-50 ps for the excitonic UV lines peaked at ~380 nm were found, indicative of ultrafast trapping of excitons by defects states inside the band gap. Compared to its as-grown precursor, the ZnO epilayer subjected to postgrowth thermal annealing in air showed enhanced intensities of both UV as well green emissions by nearly the same factor of ~3.1, in accompany with complete disappearance of the impurity luminescence peaked at 2.83 eV. More importantly, the green luminescence in the post-annealed ZnO was observed to decay as hyperbolic 1 − t and logarithmically shift its peak emission toward higher energies with increased excitation intensity, in excellent agreement with the tunnel-assisted donor-acceptor pair(DAP) recombination model. The possible mechanism of compensation between intrinsic impurities was also discussed.

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Time-resolved photoluminescence in ZnO epitaxial thin films studied by up-conversion method

Cited by 38 publications

References 11 publications

Conversion of an electron–hole plasma into a high density excitonic state in ZnO epitaxial thin films

Conversion of an electron–hole plasma into a high density excitonic state in ZnO epitaxial thin films

Intensity-dependent dynamics of photoexcited carriers in ZnO epilayers studied using pump-probe reflectance

Time-integrated and time-resolved photoluminescence in ZnO epitaxial thin films grown onto (100) silicon substrates by MOCVD

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