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Article

Electric Properties of n-GaN: Effect of Different Contacts on the Electronic Conduction

1Department of Physics, Faculty of Science, King Abdul-Aziz University, Jeddah, Saudi Arabia


International Journal of Physics. 2013, 1(2), 41-48
DOI: 10.12691/ijp-1-2-3
Copyright © 2013 Science and Education Publishing

Cite this paper:
S. Abdalla, F. Marzouki, S. Al-ameer, S. Turkestani. Electric Properties of n-GaN: Effect of Different Contacts on the Electronic Conduction. International Journal of Physics. 2013; 1(2):41-48. doi: 10.12691/ijp-1-2-3.

Correspondence to: S. Abdalla, Department of Physics, Faculty of Science, King Abdul-Aziz University, Jeddah, Saudi Arabia. Email: smabdullah@kau.edu.sa

Abstract

The forward current–voltage (I–V) characteristics of n-GaN films on sapphire substrate are investigated over a temperature range of 80–300K, using two different types of metal/semiconductor contacts: Al/GaN and Au/GaN. Samples with Al metallic contacts show well defined ohmic behavior with linear forward and reverse I-V characteristics indicating no potential barrier. These measurements made at temperatures in the range 77K-300K show the influence of two donor levels: one is deep at 0.23ev, while the other is shallow at 0.013ev below the conduction band. These values have been confirmed by DSCL measurements and the density of electrons n0 is calculated as a function of temperature and found that n0 = 3.08x10^14cm-3 at 300K. Besides, the mobility of electrons µ has been calculated as a function of temperature and have been found that at 300K: µ = 175cm2/v.s. On the other hand, resistively deposited Au Schottky contacts on n-type GaN show net rectification behavior. In contrast to the published data, the I-V measurements revealed that these Au contacts exhibited bad rectification properties: relatively high reverse current and bad ideality factor (n = 11.5 at 80K). This discrepancy has been attributed to the presence of a series resistance with the Au/n-GaN Schottky diode. The potential drop across this resistance decreases n from 11.5 down to a logic value 1.2 at 80K. Index Terms—GaN diode; contact resistance; ideality factor; transport mechanism.

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Article

Pulsed Laser Impact on Ferrimagnetic Nanostructures

1Department of Nanostructure Physics, Institute of Magnetism NASU, Kyiv, Ukraine


International Journal of Physics. 2013, 1(2), 28-40
DOI: 10.12691/ijp-1-2-2
Copyright © 2013 Science and Education Publishing

Cite this paper:
Mykola Krupa, Andrii Korostil. Pulsed Laser Impact on Ferrimagnetic Nanostructures. International Journal of Physics. 2013; 1(2):28-40. doi: 10.12691/ijp-1-2-2.

Correspondence to: Andrii Korostil, Department of Nanostructure Physics, Institute of Magnetism NASU, Kyiv, Ukraine. Email: amand@rambler.ru

Abstract

We have studied the mechanisms of a pulsed laser impact on the magnetization conFigureuration in ferrimagnetic multilayered magnetic nanostructures, specifically, tunneling magnetic junctions. The mechanism of such the laser-induced impact is a complex process of laser-induced thermal demagnetization of magnetic sublattices with subsequent biasing by internal magnetic fields of different nature. Depending on an intensity of laser pulses it can be effective internal magnetic fields of laser irradiation or internal magnetic fields connected with different rates of the heat demagnetization of ferrimagnetic sublattices. It is shown that investigated ferrimagnetic nanostructure are characterized very small times of the laser-induced remagnetization, which can attain subpicosecond scales.

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Article

Performance Assessment of the Waterjet Propulsion System through a Combined Analytical and Numerical Approach

1Department of Marine Technology, Amirkabir University of Technology, Tehran, Iran


International Journal of Physics. 2013, 1(2), 22-27
DOI: 10.12691/ijp-1-2-1
Copyright © 2013 Science and Education Publishing

Cite this paper:
Parviz Ghadimi, Roya Shademani, Mahdi Yousefi Fard. Performance Assessment of the Waterjet Propulsion System through a Combined Analytical and Numerical Approach. International Journal of Physics. 2013; 1(2):22-27. doi: 10.12691/ijp-1-2-1.

Correspondence to: Parviz Ghadimi, Department of Marine Technology, Amirkabir University of Technology, Tehran, Iran. Email: pghadimi@aut.ac.ir

Abstract

The application of waterjets is rapidly growing and they are increasingly being chosen for propulsion in high-speed crafts. Waterjet as a propulsion system of a vessel is also favorable when it comes to maneuvering, appendage drag, draft and fuel consumption at high speeds. Furthermore, waterjet system has recently gained more credibility for its acceptable efficiency because of the advent of more efficient and large pumps. This type of propulsion system consists of many components working together harmoniously, thus establishing a complex system. A significant problem facing designers when predicting performance of the waterjet is the interaction between the hull and the waterjet. This paper describes the powering performance of a vessel equipped with a waterjet system. The interaction between the hull and waterjet is studied in order to predict the powering characteristics. The work starts with an introduction of the waterjet and a review of its current status in design and analysis. Subsequently, hydrodynamic properties of its components are computed and interactions among them are analyzed. Finally, numerical computation is performed for acquiring pressure distribution by a two dimensional computer code in the suction area of the waterjet inlet to predict the possible occurrence of cavitation for the inlet duct.

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