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ABSTRACT: Nominally undoped, hydrothermally grown ZnO single crystals have been investigated
before and after exposure to remote H-plasma. Defect characterization has been made by two
complementary techniques of positron annihilation: positron lifetime spectroscopy and coincidence
Doppler broadening. The high-momentum parts of the annihilation photon momentum distribution
have been calculated from first principles in order to assist in defect identification. The positron
annihilation results are supplemented by Atomic Force Microscopy for characterization of the
crystal surface. It was found that virgin ZnO crystal contains Zn-vacancies associated with
hydrogen. H-plasma treatment causes a significant reduction in concentration of these complexes.
Physical mechanism of this effect is discussed in the paper.
Defect and Diffusion Forum 09/2012; 331:113.
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ABSTRACT: Homoepitaxial ZnO films deposited on annealed hydrothermal O-face ZnO single crystals show superior structural quality. This is demonstrated by narrow ZnO(00.2) rocking curves with FWHM of typically 23 to 35 arcsec, and nearly dislocation-free TEM cross sections. Nominally undoped ZnO films indicate a minor in-plane strain of about 250 ppm and no out-of-plane strain. Target doping by 0.01% P2O5 or 0.5% Li3N results in pseudomorphic film growth without in-plane strain. Increasing doping concentration of 0.1 and 1% P2O5 results in both in-plane and out-of-plane strain up to 0.9% indicating relaxed films. The O-face polarity of the homoepitaxial ZnO films is confirmed by convergent beam electron diffraction. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 07/2008; 5(10):3280 - 3287.
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Integrated Optoelectronic Devices 2008; 01/2008
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PROCEEDINGS-SPIE THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING. 01/2008; 6895:6895.
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ABSTRACT: MgZnO thin films, MgZnO/ZnO heterostructures (HS) and double heterostructures (DHS) have been prepared on a-plane sapphire
substrates by means of pulsed laser deposition (PLD). A linear blueshift of the MgZnO emission with increasing Mg content
is observed in photoluminescence spectroscopy (PL) at 2K. Cathodoluminescence measurements verify the spatial homogeneity
of the emission properties of the MgZnO films. The film roughness is evaluated from atomic force microscopy scans. In MgZnO/ZnO
HS the ZnO grows on all appearing MgZnO facets. PL investigations of such PLD-grown heterostructures show the high optical
quality of thin ZnO films (d≤100nm) grown on MgZnO. Capping those structures with a thin MgZnO layer further improves their
luminescence intensity and enhances the emission of free-exciton luminescence from the ZnO layers. MgZnO/ZnO/MgZnO DHS with
nominal ZnO layer thicknesses of dnom≤6nm show a clear intensification of the ZnO PL. Temperature dependent PL and transmission measurements between 4.4 and 300K
prove the dominating emission to be due to the recombination of excitons localized in the ZnO. At 2K, due to confinement
effects, their emission energy is blueshifted up to 51meV compared to free excitons in bulk ZnO.
Applied Physics A 06/2007; 88(1):99-104. · 1.63 Impact Factor
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H. von Wenckstern,
G. Benndorf,
S. Heitsch,
J. Sann,
M. Brandt, H. Schmidt,
J. Lenzner,
M. Lorenz,
A.Y. Kuznetsov,
B.K. Meyer,
M. Grundmann
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ABSTRACT: We report the electrical and optical properties of P-doped epitaxial ZnO thin films grown heteroepitaxially on sapphire substrates
or homoepitaxially on ZnO wafers grown by the hydrothermal method, respectively. As-grown heteroepitaxial thin films exhibit
semi-insulating to strongly n-conducting behavior depending on the P-content and the oxygen partial pressure applied during
deposition. New features are observed in the recombination spectra compared to nominally undoped ZnO thin films. The spectral
position of these new features also depends on the growth conditions making a clear correlation between P-incorporation and
particular spectral features feasible. For the homoepitaxially grown thin films lateral scanning capacitance microscopy measurements
revealed areas of both n- and p-type majority carriers.
Applied Physics A 01/2007; 88(1):125-128. · 1.63 Impact Factor
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ABSTRACT: Epitaxial ZnO thin films on sapphire substrates can be used as fast and laterally homogeneous scintillators to convert electrons
into photons, for example for imaging purpose. We report on the improvement of the cathodoluminescence intensity of epitaxial
pulsed laser deposited ZnO films on a-plane sapphire substrates with diameter up to 33mm. The lateral homogeneity of the
integral cathodoluminescence intensity was inspected using a modified RHEED setup. Cathodoluminescence spectra were excited
at the ZnO side of the samples and detected both in reflection and in transmission geometry. The redshift of the excitonic
cathodoluminescence peak in transmission relative to reflection and the peak shift with the excitation depth can be explained
by a model based on self absorption of the photons in the ZnO film.
Applied Physics A 01/2007; 88(1):89-93. · 1.63 Impact Factor
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Thin Solid Films 01/2007; 515(24):8761-8763. · 1.89 Impact Factor
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G. Brauer,
W. Anwand,
W. Skorupa,
J. Kuriplach,
O. Melikhova,
J. Cizek,
I. Prochazka,
C. Moisson,
H. Wenckstern von, H. Schmidt,
M. Lorenz,
M. Grundmann
Superlattices Microstruct. 01/2007; 42:259.
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Phys. Rev. B. 01/2007; 76:035214.
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Appl. Phys. A. 01/2007; 88:89.
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Superlattices Microstruct. 01/2007; 42:14.
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H. Wenckstern von,
G. Benndorf,
S. Heitsch,
J. Sann,
M. Brandt, H. Schmidt,
J. Lenzner,
M. Lorenz,
A. Y. Kuznetsov,
B. K. Meyer,
M. Grundmann
Appl. Phys. A. 01/2007; 88:125.
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Superlattices Microstruct. 01/2007; 42:231.
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H. Wenckstern von, H. Schmidt,
C. Hanisch,
M. Brandt,
C. Czekalla,
G. Benndorf,
G. Biehne,
A. Rahm,
H. Hochmuth,
M. Lorenz,
M. Grundmann
phys.stat.sol. (RRL). 01/2007; 1(4):129 - 131.
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Appl. Phys. A. 01/2007; 88:157.
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Appl. Phys. A. 01/2007; 88:135.
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Appl. Phys. Lett. 01/2007; 91:022913.
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ABSTRACT: The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n -conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280 meV , respectively.
Applied Physics Letters 09/2006; · 3.84 Impact Factor
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Solid State Commun. 01/2006; 137:417.
