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Polarization Field (polarization + field)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Optimization of homoepitaxially grown AlGaN/GaN heterostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010
J. A. Grenko
Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c -axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (µRT) up to 2065,cm2,V,1,s,1 at sheet density (ns) of 8.25,×,1012,cm,2 has been measured. This work compliments prior studies in which we observed a buffer-induced modulation of the RT two-dimensional electron gas (2DEG) ns and µRT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEG properties by elimination of silicon doping in the Al0.25Ga0.75N barrier and unintentional Al in the not-intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in µRT and ns relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field () to be ,5,×,1012,cm,2. [source]

Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006
Hamid Haratizadeh
Abstract We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Polarization field crossover in semi-polar InGaN/GaN single quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010
H. Shen
Abstract We present an electroreflectance study of the polarization field in semi-polar (10) and (112) oriented InGaN quantum wells (QW). For the () sample, the flat-QW condition (the electric field in the QW is zero) is at a reverse bias voltage. For the (112) sample, the flat-QW condition is at a forward bias voltage larger than the turn on voltage of the diode. However, the flat-barrier condition (the electric field in the barrier region is zero) is at a forward bias voltage less than the turn on voltage of the diode. The flat-QW condition and the flat-barrier condition are determined by examining the zero-crossing and the Franz-Keldysh oscillations in the electroreflectance signal for (10) and (112) InGaN QWs, respectively. From the corresponding bias voltages, we deduce the polarization field in the QWs and conclude that in the semi-polar InGaN/GaN QW there is a crossover angle between the polar and non-polar orientations where the polarization field vanishes. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Modulation of mobility in homoepitaxially-grown AlGaN/GaN heterostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
J. A. Grenko
Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm,2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially-grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer-induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 ,m is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance-voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ,5x1012 cm,2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

In-plane polarization of GaN-based heterostructures with arbitrary crystal orientation

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010
Q. Y. Wei
Abstract The total polarization fields of pseudomorphic InxGa1,xN/GaN and AlxGa1,xN/GaN heterostructures with 0,,,x,,,0.4 have been calculated as a function of the crystal orientation. Especial attention is placed on the direction and magnitude of in-plane piezoelectric polarization, which is not negligible for the non-polar and semi-polar growth. For an arbitrary crystal orientation, the piezoelectric polarization prevails in the InGaN/GaN system while the spontaneous polarization prevails in the AlGaN/GaN system. The in-plane potential due to polarization fields in non-polar epilayers is found to depend on the degree of planarity of the heterojunctions, and on the respective lateral dimensions. [source]

Electromagnetic fields induced by a concentrated heat source in multiferroic materials

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2008
X. Wang
Abstract Pyroelectric and pyromagnetic effects are important for applications of multiferroic materials in elevated temperature environments. In this paper, we derive exact closed-form electromagnetic Green's function expressions for polarization fields in uniaxial multiferroic materials and bimaterials induced by a steady point heat source. The pyroelectric and pyromagnetic effects as a result of temperature change in multiferroic materials are incorporated in this study. The degen- erate and nondegenerate cases, which pertain to whether the heat conduction characteristic constant is equal to one of the two electromagnetic characteristic constants, are discussed in detail. The Green's functions for a bimaterial composed of two perfectly bonded uniaxial multiferroic half-spaces subjected to a point heat source are further obtained by means of the image method. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]