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1,071 results on '"Morkoc, H."'

1. High-field electron transport in bulk ZnO

Author

Ardaravičius, L., Liberis, J., Ramonas, M., Šermukšnis, E., Matulionis, A., Toporkov, M., Avrutin, V., Özgür, Ü., and Morkoç, H.

Subjects
Condensed Matter - Materials Science
Abstract

Current-voltage dependence is measured in (Ga,Sb)-doped ZnO up to 150 kV/cm electric fields. A channel temperature is controlled by applying relatively short (few ns) voltage pulses to two-terminal samples. The dependence of electron drift velocity on electron density ranging from 1.42$\times$10$^{17}$ cm$^{-3}$ to 1.3$\times$10$^{20}$ cm$^{-3}$ at a given electric field is deduced after estimation of the sample contact resistance and the Hall electron mobility. Manifestation of the highest electron drift velocity up to $\sim$1.5$\times$10$^{7}$ cm/s is estimated for electron density of 1.42$\times$10$^{17}$ cm$^{-3}$ and is in agreement with Monte Carlo simulation when hot-phonon lifetime is below 1 ps. A local drift velocity maximum is observed at $\sim$1.1$\times$10$^{19}$ cm$^{-3}$ and is in agreement with ultra-fast hot phonon decay., Comment: 9 pages, 4 figures, 1 table

Published
2016

3. Illumination and annealing characteristics of two-dimensional electron gas systems in metal-organic vapor-phase epitaxy grown AlGaN/AlN/GaN heterostructures

Author

Biyikli, N., Ozgur, U., Ni, X. F., Fu, Y., Morkoc, H., and Kurdak, C.

Subjects
Condensed Matter - Materials Science
Abstract

We studied the persistent photoconductivity (PPC) effect in AlGaN/AlN/GaN heterostructures with two different Al-compositions (x=0.15 and x=0.25). The two-dimensional electron gas formed at the AlN/GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N/AlN/GaN sample from 1.6x10^{12} cm^{-2} to 5.9x1012 cm^{-2}, while the electron mobility was enhanced from 9540 cm2/Vs to 21400 cm2/Vs at T = 1.6 K. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength, being highest close to the bandgap and decreasing at longer wavelengths. The PPC effect became fairly weak for illumination wavelengths longer than 530 nm and showed a more complex response with an initial negative photoconductivity in the infrared region of the spectrum (>700 nm). The maximum PPC-efficiency for 390 nm illumination was 0.011% and 0.005% for Al0.25Ga0.75N/AlN/GaN and Al0.15Ga0.85N/AlN/GaN samples, respectively. After illumination, the carrier density could be reduced by annealing the sample. Annealing characteristics of the PPC effect were studied in the 20-280 K temperature range. We found that annealing at 280 K was not sufficient for full recovery of the carrier density. In fact, the PPC effect occurs in these samples even at room temperature. Comparing the measurement results of two samples, the Al0.25Ga0.75N/AlN/GaN sample had a larger response to illumination and displayed a smaller recovery with thermal annealing. This result suggests that the energy scales of the defect configuration-coordinate diagrams for these samples are different, depending on their Al-composition., Comment: 27 pages, 8 figures

Published
2006
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4. Weak antilocalization and zero-field electron spin splitting in AlGaN/AlN/GaN heterostructures with a polarization induced two-dimensional electron gas

Author

Kurdak, C., Biyikli, N., Ozgur, U., Morkoc, H., and Litvinov, V. I.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Spin-orbit coupling is studied using the quantum interference corrections to conductance in AlGaN/AlN/GaN two-dimensional electron systems where the carrier density is controlled by the persistent photoconductivity effect. All the samples studied exhibit a weak antilocalization feature with a spin-orbit field of around 1.8 mT. The zero-field electron spin splitting energies extracted from the weak antilocalization measurements are found to scale linearly with the Fermi wavevector with an effective linear spin-orbit coupling parameter 5.5x10^{-13} eV m. The spin-orbit times extracted from our measurements varied from 0.74 to 8.24 ps within the carrier density range of this experiment., Comment: 16 pages, 4 figures

Published
2006
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13. Luminescence of AlN/GaN superlattices implanted with Tb and Tm ions

Author

Jadwisienczak, W.M., Ramani, J., Lozykowski, H.J., Xi, J., Morkoc, H., and Anders, A.

Subjects
luminescence, AlN / GaN superlattice
Abstract

Studies on the optically active rare earth (RE) ions doped III-nitrides QWs and SLs are very scarce, however available data indicates significant improvement in the PL intensities of Eu and Er doped AlGaN/GaN superlattices. Despite encouraging initial results, the mechanism for transfer of excitation from electrons and holes produced by electron or photon pumping in such structures is still not entirely clear. As demonstrated by GaN laser diodes, light emitting diodes (LED), and GaN based electronic devices, all GaN based devices must take advantage of quantum well (QW) structures such as GaN/AlGaN, InGaN/GaN and GaN/AlN. In order to optimize the device design using RE-doped III-nitrides, it is necessary to study and understand the physical properties of RE doped nitride QWs and SLs as well as the QW structural effects on the device performance.

Published
2006

45. Illumination and annealing characteristics of two-dimensional electron gas systems in metal-organic vapor-phase epitaxy grown [Al.sub.x][Ga.sub.1-x]N/AlN/GaN heterostructures

Author

Biyikli, N., Ozgur, U., X. Ni, Y. Fu, Morkoc, H., and Kurdak, C.

Subjects
Hall effect -- Research, Aluminum nitride -- Optical properties, Aluminum nitride -- Electric properties, Photoconductivity -- Research, Gallium compounds -- Electric properties, Gallium compounds -- Optical properties, Physics
Abstract

The persistent photoconductivity (PPC) effect in [Al.sub.x][Ga.sub.1-x]N/AlN/GaN heterostructures with was studied with two different Al compositions. The PPC effect became fairly weak for illumination wavelengths longer than approximately 530nm and showed a more complex response with an initial negative photoconductivity in the infrared region.

Published
2006

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