Home About us Contact
|
Home About us Contact | ||
|
|
||
Two-dimensional Electron Gas (two-dimensional + electron_gas)
Selected AbstractsOptimization of homoepitaxially grown AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010J. 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] Spin-filtering effect in a two-dimensional electron gas under a local fringe fieldPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Seon-Gu Huh Abstract We fabricated a spin-filtering device which consists of InAs based two-dimensional electron gas and two ferromagnetic pads. A fringe field at the edge of a ferromagnetic pad was used to induce spin polarization of the moving electrons in a two-dimensional electron gas. The direction of the fringe field was determined by the magnetization of the ferromagnetic pad, which was switched by using the external magnetic field. A current of which spins were aligned by one fringe field (polarizer) was filtered by the other fringe field (analyzer). The resistance of the device was in either a high state or a low state depending on the alignment of the fringe fields. The spin-filtering effect diminishes rapidly as the thermal energy exceeds the Zeeman splitting. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hot phonons in GaN channels for HEMTsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2006A. Matulionis Abstract Accumulation of non-equilibrium longitudinal optical (LO) phonons (termed hot phonons) is considered as a possible cause for limitation of hot-electron drift velocity at high electric fields in a GaN biased channel with a two-dimensional electron gas (2DEG). Equivalent hot-phonon temperature and hot-phonon lifetime are estimated from experimental results on hot-electron noise at a microwave frequency. Dependence of the hot-phonon parameters on electron density and channel composition is investigated, and frequency performance of high-electron-mobility transistors (HEMTs) is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Current imaging in quantum point contactsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006Alessandro Cresti Abstract The experimental imaging of microscopic currents in two-dimensional electron gas based systems has been recently realized exploiting an ingenious use of scanning microscope tips. By means of the Keldysh Green's function formalism in a tight-binding framework, I study the electron transport in a model quantum point contact device, obtaining detailed maps of the local current distribution. The results are then compared with those obtained by a direct simulation of the experimental process, i.e. introducing a suitable external potential to reproduce the effect of the coupled microscopic tip on the overall conductance and the electron flow. The analysis of the differences between the two calculations helps to interpret the experimental maps and sheds light on the interference effects of the tip. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polarization effects in 2-DEG and 2-DHG AlGaN/AlN/GaN multi-heterostructures measured by electron holographyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010Q. Y. Wei Abstract The electrostatic potential profiles and charge distributions in modulation-doped n-type and p-type AlGaN/AlN/GaN heterostructures have been measured by electron holography with high spatial resolution. For n-type two-dimensional electron gas structure a negative curvature and for p-type two-dimensional hole gas structure a positive curvature in the potential profile at the AlN/GaN interface were observed, which demonstrated the accumulation of two-dimensional carriers. The measured electrostatic potential profiles were also compared with the calculated band diagram in the heterostructures. [source] Ultrafast decay of non-equilibrium (hot) phonons in GaN-based 2DEG channelsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009Arvydas MatulionisArticle first published online: 27 OCT 200 Abstract Fast and ultrafast decay of non-equilibrium longitudinal optical phonons (hot phonons) is discussed on examples of two-dimensional electron gas (2DEG) channels confined in nominally-undoped nitride and selectivelydoped arsenide heterostructures subjected to pulsed dc electric power. At a low,moderate power, a nonmonotonous dependence of the hot-phonon lifetime on the 2DEG density is found. The fastest decay takes place at ,2.5 × 1012 cm,2 in GaInAs 2DEG channel and at ,7 × 1012 cm,2 in GaN 2DEG channel. The result is discussed in terms of plasmon,LO-phonon resonance. The hot-phonon lifetime decreases when the supplied power is increased if the 2DEG density exceeds the resonance density. The shortest hot-phonon lifetime of 60 fs is obtained at/above 50 nW/electron for the lattice-matched AlInN/AlN/GaN 2DEG channel (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhancement in electrical properties of GaN heterostructure field-effect transistor by Si atom deposition on AlGaN barrier surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Norio Onojima Abstract This study demonstrates that deposition of Si atoms on AlGaN barrier surfaces in GaN heterostructure field-effect transistors (HFETs) can modulate the electrical properties of the two-dimensional electron gas (2DEG). The results of Hall measurements performed using the eddy current and four-point van der Pauw methods showed that the sheet resistance of an AlGaN/GaN HFET sample without surface passivation increased from that of the unprocessed sample after post-metallization annealing at 820 °C for ohmic contacts. In contrast, the sheet resistance of the Si-deposited sample did not increase even after annealing. Furthermore, eddy current measurements for unprocessed wafers with and without Si deposition revealed that the sheet resistance can be reduced by depositing Si atoms, regardless of annealing. The effect of Si deposition on devices having a thin Al-rich barrier layer was found to be significant. The deposition of Si atoms (2 nm) on the AlN barrier surface in an AlN/GaN HFET (AlN 2 nm) resulted in a remarkable decrease in the sheet resistance from 60356 to 388 ,/sq. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of barrier thickness on AlInN/AlN/GaN heterostructures and device propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009H. Behmenburg Abstract We report on structural and device properties of AlInN/AlN/GaN transistor heterostructures grown by metal organic vapour phase epitaxy (MOVPE) on 2, sapphire substrates with AlInN barriers of thicknesses between 4 nm and 10 nm. The In content and thickness of the thin AlInN barrier is shown to be well determinable by high-resolution X-ray diffraction (HRXRD). Room temperature Hall measurements yielded similar mobility between 1400 cm2V,1s,1 and 1520 cm2V,1s,1 on all samples and increasing sheet carrier concentration ns with rising barrier thickness resulting in a minimum sheet resistance value of 200 Ohm/,. The effect of surface passivation with Si3N4 on the electrical properties is investigated and found to strongly increase sheet carrier concentration ns of the two-dimensional electron gas (2DEG) to values above 2×1013cm,2. Characterization of transistors with gate length Lg of 1.5 ,m produced from the grown samples reveals high transconductance (gm) and a maximum drain current (ID) of 300 mS/mm and ,1 A/mm, respectively. For the sample with 4.6 nm barrier thickness, a reduced gate leakage current (IGL) and a absolute value of the threshold voltage (Vth) of -1.2 V is detected. Radio frequency (RF) measurements of passivated samples lead to maximum current gain cut-off frequencies ft of 11 GHz and maximum oscillating frequencies fmax of 25 GHz. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of minority carrier lifetime for InAlAs/InGaAs high electron mobility transistors by using 1.55-,m femto-second pulse laserPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008Hirohisa Taguchi Abstract The minority carrier lifetime (,) of High electron mobility transistors (HEMTs) made using the InAlAs/InGaAs material system lattice-matched to the InP substrate had been obtained from optical response measurements with a 1.55-,m femto-second pulse laser where the laser was illuminated onto the backside of a wafer. The drain current of HEMTs associated with the optical pulse was detected using a digitizing oscilloscope, and , was estimated from the exponential dependence of drain current on time. In our current investigation, we found that , is dominated by the following modes: (1) the amount of time required for holes to transit across the channel toward the source, and (2) the amount of time required for the holes accumulated in the source region to recombine with two-dimensional electron gas (2DEG) through the Auger mechanism. Because the sheet concentration (ps) of holes accumulated in source region is low at a low source-to-drain voltage (VDS), Auger recombination is not predominant, and , was only dominated by the hole transit time. At a high VDS, ps became high enough for Auger recombination to occur and dominate ,. Furthermore, we investigated the optical power dependence of , where the optical power was supplied in a continuous wave (CW) to generate photo-excited holes in a steady state. The value of , decreased monotonically as VDS increased and saturated in as little as 6x10,10 s when the optical power was increased. The theoretical investigation was made to understand this saturation phenomenon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN/GaN-based MEMS with two-dimensional electron gas for novel sensor applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008F. Niebelschütz Abstract Novel microelectromechanical resonators structures have been realized based on AlGaN/GaN heterostructures, which provide a basis for sophisticated sensor structures. There were grown on SiC substrates confining a two dimensional electron gas (2DEG). By means of the developed etching technology, freestanding resonators were patterned without degrading the sheet carrier concentration and electron mobility of the 2DEG inside the beams, which was confirmed by electrical measurements before and after the various process steps. As actuation and read out principle magnetomotive and piezoelectric effects were used, respectively. Due to the high sensitivity of the 2DEG and the chemical stability of the utilized materials these structures are suitable for chemical and biological sensor applications, where the sensitivity of the 2DEG on the surrounding environment acts as additional sensing signal, for example for simultaneous measurements of the viscosity and pH , value of a nanoliter droplet. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nitride based nanotransistors as new sources and detectors of THz radiationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008A. El Fatimy Abstract The plasma waves in gated two-dimensional electron gas have a linear dispersion law, similar to the sound waves. The transistor channel is acting as a resonator cavity for the plasma waves, which can reach frequencies in the Terahertz (THz) range for a sufficiently short gate length Field Effect Transistors (FETs). THz emission and detection by nanometer III-V transistors have been recently reported. In this work we report on THz emission and detection by nanometer GaN/AlGaN HEMTs. In particular, we show that specific GaN properties allow to observe THz emission up to room temperature. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of electron-electron interaction on the diffusion current of spin-polarized electronsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Yutaka Takahashi Abstract Electron-electron interaction modifies carrier transport in the spin-polarized system. The effects are investigated in the two-dimensional electron gas in semiconductor heterostructures. We find that the diffusion currents of spin-up and spin-down electrons are reduced, compared to the non-interacting values, by the momentum exchange between spin-up and spin-down electrons through their collisions (Spin Drag), and also by the electron energy renormalization arising from the manyparticle correlations. We numerically calculate the diffusion coefficients of spin-up and spin-down electrons separately in high-quality heterostructures of GaAs at low temperatures, including the effect of finite spin life time. Our calculations show that the diffusion coefficients are reduced down to less than half of their non-interacting values. We also find the negative diffusivity at low temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] XPS study of surface potential in AlGaN/GaN heterostructure with Cat-CVD SiN passivationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007N. Onojima Abstract AlGaN surface potentials in AlGaN/GaN heterostructures with and without SiN passivation were investigated using x-ray photoelectron spectroscopy (XPS). SiN films were formed on AlGaN surfaces by catalytic chemical vapor deposition (Cat-CVD), which has already been found to increase two-dimensional electron gas (2DEG) density. Based on a simple electrostatic analysis, the 2DEG density is expected to increase as the AlGaN surface potential decreases. This study experimentally demonstrates that a reduction in the AlGaN surface potential is actually induced by Cat-CVD SiN passivation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of electrical properties of insulators (Si3N4, SiO2, AlN, and Al2O3)/0.5 nm Si3N4/AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Narihiko Maeda Abstract The electrical properties in AlGaN/GaN heterostructures with Si- and Al-based insulators (Si3N4, SiO2, AlN, and Al2O3) have been examined and analyzed. By insulators deposition, significant increase in the two-dimensional electron gas (2DEG) density (Ns) was observed with the order of Ns(Al2O3) > Ns(AlN) , Ns(SiO2) > Ns(Si3N4) > N0 (N0: Ns without insulators). As the result, the decrease in the sheet resistance (R) was observed; the smallest order of R was R(Al2O3) < R(AlN) < R(Si3N4) < R0 , R(SiO2) (R0: R without insulator). The insulators deposition effect has thus been shown to be significant and different among insulators. The increase in Ns was analyzed in terms of the change in the potential profile, and the observed differences in Ns among insulators have been interpreted. The band engineering including insulators is indispensable in understanding and designing AlGaN/GaN HFETs, since insulators are commonly used for the surface passivation as well as for the gate insulators, and the insulators deposition is to alter the essential device parameters such as the source resistance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-field electron transport in AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005J. M. Barker Abstract Experimental studies have been performed on the velocity-field characteristics of AlGaN/GaN heterostructures. A pulsed voltage input in combination with a four-point measurement was used in a 50 , environment to determine the drift velocity of electrons in the two-dimensional electron gas as a function of the applied electric field. These measurements show an apparent saturation velocity near 3.1 × 107 cm/s, at a field of 140 kV/cm. A comparison of these studies shows that the experimental velocities are close to previously published simulations based upon Monte Carlo techniques. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hot-electron transport in III,V nitride based two-dimensional gasesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003S. A. Vitusevich Abstract We report on experimental and theoretical studies of low and high field transport in AlGaN/GaN two-dimensional electron gas (2DEG). Magnetotransport of 2DEG created as a result of polarization effects at the heterointerface has been studied. The velocity-electric field characteristics extracted from pulsed current,voltage measurements in AlGaN/GaN heterostructures are in good agreement with transport calculations up to fields as high as 100 kV/cm. [source] Two-Dimensional Electron Dynamics in GaN/AlGaN HeterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003S.A. Vitusevich Abstract This report addresses the study of two-dimensional electron gas (2DEG) transport at low and moderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN) gateless heterostructures grown on sapphire for HEMT applications. The transmission line model (TLM) patterns of different channel lengths L and the same channel width are used. We have developed a simple theoretical model to adequately describe the observed peculiarities in the I,V characteristics measured in steady-state and pulsed (10,6 s) regimes. The effect of Joule heating of a heterostructure is clearly distinguished. The thermal impedances and the channel temperature rise caused by the Joule self-heating have been extracted for the devices of different L at different values of dissipated power. [source] | ||||||||||