Electron Hall Mobility Research Articles

Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2Se3under high pressure

This paper reports an experimental and theoretical investigation on the electronic structure of bismuth selenide (Bi${}_{2}$Se${}_{3}$) up to 9 GPa. The optical gap of Bi${}_{2}$Se${}_{3}$ increases from 0.17 eV at ambient pressure to 0.45 eV at 8 GPa. The quenching of the Burstein-Moss effect in degenerate samples and the shift of the free-carrier plasma frequency to lower energies reveal a quick decrease of the bulk three-dimensional (3D) electron concentration under pressure. On increasing pressure the behavior of Hall electron concentration and mobility depends on the sample thickness, consistently with a gradual transition from mainly 3D transport at ambient pressure to mainly two-dimensional (2D) transport at high pressure. Two-carrier transport equations confirm the trapping of high-mobility 3D electrons, an effect that can be related to a shallow-to-deep transformation of donor levels, associated with a change in the ordering of the conduction band minima. The high apparent areal density and low electron mobility of 2D electrons are not compatible with their expected properties in a Dirac cone. Measured transport parameters at high pressure are most probably affected by the presence of holes, either in an accumulation surface layer or as minority carriers in the bulk.

Comparative Study of Electrical and Microstructural Properties of 4H-SiC MOSFETs

N-channel MOSFETs were manufactured on p-type and on p-implanted, n-type 4H-SiC substrates. The electron mobility in the inversion channel was measured to be correlated with the structural and chemical properties determined by transmission electron microscopy. With regard to what was previously discussed in the literature, interfacial layer formation and carbon distribution across the SiC/SiO2 interface were considered in relation with the measured Hall electron mobility.

Electron drift-mobility measurements in polycrystalline CuIn1−xGaxSe2 solar cells

We report photocarrier time-of-flight measurements of electron drift mobilities for the p-type CuIn1−xGaxSe2 films incorporated in solar cells. The electron mobilities range from 0.02 to 0.05 cm2/Vs and are weakly temperature-dependent from 100–300 K. These values are lower than the range of electron Hall mobilities (2-1100 cm2/Vs) reported for n-type polycrystalline thin films and single crystals. We propose that the electron drift mobilities are properties of disorder-induced mobility edges and discuss how this disorder could increase cell efficiencies.

Room Temperature Deposition of Highly Transparent n-ZnO on PET and ZnO Semiconductor FET

ABSTRACTIn this paper we report on the fabrication of n-doped ZnO and semiconducting n-ZnO at room temperature by a new ablation deposition technology that makes use of electron/plasma ablation sources named Pulsed Plasma Deposition (PPD) developed by Organic Spintronics Srl.The oxygen vacancies n-doped ZnO PPD grown thin film is deposited on PET and shows a resistivity of 3 x 10-4ohm cm. The n-ZnO TCO is compact, smooth and highly transparent in the UV-VIS (better than 90 T%) as well as in the near IR spectral range and it is remarkably temperature stable. Typical ZnO deposition rate of the PPD is 500 nm/min.The RT deposited semiconductor ZnO shows a very large Hall electron mobility up to 1000 cm2/Vs approaching that of the single crystal. Preliminary results of Si/SiO2 based bottom gate and contact FET test pattern structures with a 50 nm overlaying ZnO thin film shows an ON/OFF ratio of 50000 and a FET mobility of 1 cm2/Vs. Further implementation on appropriate FET design will be performed to explore the possibility to achieve a larger FET mobility. The PPD proves to be an enabling technology that makes it possible the advent of flexible OLED displays.

Electrical properties of β-Ga2O3 single crystals grown by the Czochralski method

Electrical properties of nominally undoped β-Ga2O3 crystals grown by the Czochralski method from an iridium crucible under a carbon dioxide containing atmosphere were studied by temperature dependent conductivity and Hall effect measurements as well as deep level transient spectroscopy. All crystals were n-type with net donor concentrations between 6 × 1016 and 8 × 1017 cm−3. The Hall mobility of electrons was on average 130 cm2/Vs at room temperature and attained a maximum of 500 cm2/Vs at 100 K. The donor ionization energy was dependent on the donor concentration. Extrapolation of this dependence to zero concentration yielded a value of about 36 meV for isolated donors agreeing well with the ionization energy derived from effective-mass theory. Three deep electron traps were found at 0.55, 0.74, and 1.04 eV below the conduction bandedge. The trap at EC – 0.74 eV was detected in all samples with concentrations of 2 – 4 × 1016 cm−3. This concentration is comparable to that of compensating acceptors we have to take into account for an explanation of the temperature dependent electron density. Therefore, under the assumption that the electron trap at EC – 0.74 eV possesses acceptor character, this trap could be the dominating compensating acceptor in our crystals. Besides, a value of ΦB = (1.1 ± 0.1) V was determined for the Schottky barrier height of Ni on the (100) surface of n-type β-Ga2O3.

220-GHz Quaternary Barrier InAlGaN/AlN/GaN HEMTs

Depletion-mode high-electron mobility transistors (HEMTs) based on a quaternary barrier <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{In}_{0.13}\hbox{Al}_{0.83}\hbox{Ga}_{0.04}\break\hbox{N/AlN/GaN}$</tex> </formula> heterostructure on SiC substrate were fabricated. The 66-nm-long gate device shows a dc drain current density of 2.1 A/mm, a peak extrinsic transconductance of 548 mS/mm, and a record current gain cutoff frequency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}$</tex></formula> of 220 GHz for quaternary barrier GaN-based HEMTs, which is also among the highest <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}$</tex></formula> for all GaN-based HEMTs. The large <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L_{g} \cdot f_{T}$</tex></formula> product of 14.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{GHz} \cdot \mu\hbox{m}$</tex></formula> with a gate-length-to-barrier-thickness aspect ratio of 5.8 indicates a high effective electron velocity of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{0.9} \times \hbox{10}^{7}\ \hbox{cm/s}$</tex></formula> , attributed to a high electron Hall mobility (1790 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{cm}^{2}/\hbox{V} \cdot \hbox{s}$</tex> </formula> at an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n_{s}$</tex></formula> of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \hbox{1.8} \times \hbox{10}^{13}\ \hbox{cm}^{-2}$</tex></formula> )—the highest reported in GaN-channel HEMTs with In-containing barriers. An intrinsic electron velocity of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{1.7} \times \hbox{10}^{7}\ \hbox{cm/s}$</tex></formula> , extracted from conventional Moll delay-time analysis, is comparable to that reported in the state-of-art AlGaN/GaN HEMTs.

Electron Mobility in Moderately Doped Si&lt;sub&gt;1-x&lt;/sub&gt;Ge&lt;sub&gt;x&lt;/sub&gt;

Si1-xGex alloys with small atomic fraction of Ge, x≤ 0.05 are investigated. The Hall mobility of electrons in n-type materials was measured at cryogenic temperatures, T≤ 100 K. Taking into account the partial mobility due to charge carrier scattering by ionized centers and phonons it is possible to estimate the partial mobility associated with alloy scattering. It appears that this contribution to the electron mobility in n-Si1-xGex at low temperatures is important even at x≈0.01. The obtained results can be useful for understanding the nature of SiGe alloys and their transport properties.

Low resistance Ti/Au contacts to amorphous gallium indium zinc oxides

We report on low-resistance Ti (50 nm)/Au (80 nm) contacts to amorphous gallium indium zinc oxides (a-GIZO). The specific contact resistances obtained using the transmission line method were as low as 2.85×10−5 Ω cm2 when annealed at 500 °C for 1 min in N2 ambient. This could be attributed to the combined effects of structural relaxation of a-GIZO films at elevated temperatures, causing drastic increases in both electron concentration and Hall mobility, and to interfacial reactions between Ti/Au and a-GIZO layers producing oxygen vacancies near the surface.

ELECTRON SCATTERING IN BURIED InGaAs/HIGH-K MOS CHANNELS

Hall electron mobility in buried QW InGaAs channels, grown on InP substrates with HfO 2 gate oxide, is analyzed experimentally and theoretically as a function of top barrier thickness and composition, carrier density, and temperature. Temperature slope α in μ ~Tα dependence is changing from α=-1.1 to +1 with the reduction of the top barrier thickness indicating the dominant role of remote Coulomb scattering (RCS) in interface-related contribution to mobility degradation. Insertion of low-k SiO x interface layer formed by oxidation of thin in-situ MBE grown amorphous Si passivation layer has been found to improve the channel mobility, but at the expense of increased EOT. This mobility improvement is also consistent with dominant role of RCS. We were able to a obtain a reasonable match between experiment and simple theory of the RCS assuming the density of charges at the high-k/barrier interface to be in the range of (2-4)×1013 cm-2.

Effect of Substrate Removal on the Optoelectronic Properties of GaAs Epitaxial Layers and GaAs/AlGaAs Vertical-Cavity Surface-Emitting Lasers

We measured the electron Hall mobility of Si-doped GaAs epitaxial layers (ELs) that were flip-chip-bonded onto an alumina mount to investigate how the quality of the thin layer changes before and after GaAs substrate removal. The electron Hall mobilities at room temperature before and after substrate removal were almost unchanged. Photoluminescence spectra after substrate removal exhibited peak wavelengths at 872-874 nm, which were almost equal to those before substrate removal. This indicates that the quality of ELs was maintained after the process. We measured near-field patterns (NFPs) and far-field patterns (FFPs) of GaAs/AlGaAs vertical-cavity surface-emitting lasers with and without a substrate. There was no change in the full-width-at-half-maximum of the NFP or in the FFP for the optical output range of 0.5-1.3 mW. We confirmed that our novel process is useful for optoelectronic packaging.

High electron mobility lattice-matched InAlN/GaN materials

InAlN can be in-plane lattice matched (LM) to GaN, and the formed InAlN/GaN heterostructure is one kind of materials with high conductivity to be used in GaN-based high electron mobility transistors (HEMTs). It is reported that the high-mobility InAlN/GaN material is grown by using pulsed metal organic chemical vapor deposition (PMOCVD) on sapphire, and the Hall electron mobility reaches 949 and 2032 cm2/Vs at room temperature and 77 K, respectively. The two-dimensional electron gas (2DEG) is formed in the sample. When 1.2 nm thick AlN space layer is inserted to form InAlN/AlN/GaN structure, the Hall electron mobility increases to 1437 and 5308 cm2/Vs at room temperature and 77 K, respectively. It is shown by analyzing the results of X-ray diffraction and atomic force microscopy and the features of PMOCVD that the crystal quality of InAlN/GaN material is quite high, and the InAlN layer LM to GaN has smooth surface and interface. The high mobility characteristics of InAlN/GaN and InAlN/AlN/GaN materials are ascribed to the fact that the 2DEG has a comparatively low sheet density (1.61013-1.81013 cm-2), the alloy disorder scattering is weakened in the high-quality InAlN crystal since its compositions are evenly distributed, and the interface roughness scattering is alleviated at the smooth interface where the 2DEG is located.

Low-temperature LPE growth and characterization of InGaAsN thick layers

Abstract This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method.

Atomic Layer Deposition of Gallium-Doped Zinc Oxide Transparent Conducting Oxide films

ABSTRACTThin transparent conducting oxide (TCO) films of gallium-doped zinc oxide have been deposited on glass substrates by atomic layer deposition (ALD) using diethyl zinc, triethyl gallium and water vapour as precursors. The gallium-doped zinc oxide films were deposited over the temperature range 100-350°C. Transmission electron microscopy reveals that the as-deposited films are polycrystalline in character. The electrical resistivity of the gallium-doped zinc oxide films was evaluated using four-point probe and contactless measurement methods as a function of film thickness. The lowest sheet resistance of 16 Ω/☐ was measured from a film thickness of 400nm and a gallium content of 5 atomic percent. The electron Hall mobility of this film was 12.3 cm2/Vs. The visible transmittance of the films was 78% with a haze of 0.2%.

Anisotropic weakly localized transport in nitrogen-doped ultrananocrystalline diamond films

We establish the dominant effect of anisotropic weak localization (WL) in three dimensions (3D) associated with a propagative Fermi surface on the conductivity correction in heavily nitrogen-doped ultrananocrystalline diamond (UNCD) films based on magnetoresistance studies at low temperatures. Also, low-temperature electrical conductivity can show weakly localized transport in 3D combined with the effect of electron-electron interactions in these materials, which is remarkably different from the conductivity in two-dimensional WL or strong localization regime. The corresponding dephasing time of electronic wave functions in these systems described as $\ensuremath{\sim}{T}^{\ensuremath{-}p}$ with $p&lt;1$, follows a relatively weak temperature dependence compared to the generally expected nature for bulk dirty metals having $p\ensuremath{\ge}1$. The temperature dependence of Hall (electron) mobility together with an enhanced electron density has been used to interpret the unusual magnetotransport features and show delocalized electronic transport in these $n$-type UNCD films, which can be described as low-dimensional superlattice structures.

High temperature electron transport properties in AlGaN/GaN heterostructures

Hall electron mobility (μH) and sheet concentration (ns) in AlGaN/GaN heterostructures have been measured from 77 to 1020 K. The effect of the deposited Al2O3 layer is also investigated with varying its thickness. It is found that μH decreases monotonously with the temperature (T) and its dependence is well approximated with the function of μH=4.5×103 exp(−0.004T) in the temperatures over 350 K. The function is different from the commonly used one of μH=AT−α (α∼1.5), which indicates that the mobility is not only governed by the polar optical phonon scattering but also the deformation potential scattering plays a role. The sheet electron concentration (ns) has a weak dependence on the temperature, that is, slightly decreases with temperature in 300–570 K and increases gradually up to 1020 K. The decrease is explained by considering the reduction in the polarization (probably both spontaneous and piezoelectric) charge and the increase seems to be due to the parallel conduction through the interface between GaN buffer layer and sapphire substrate. The dependence of sheet resistance (Rsh) in AlGaN/GaN is compared with that of n-GaN. In the low temperatures, AlGaN/GaN shows a lower Rsh due to its high mobility, however, at the temperatures higher than 350 K, Rsh of AlGaN/GaN becomes higher than that of n-GaN. This result implies that AlGaN/GaN high-electron-mobility-transistors are inferior to GaN metal-semiconductor field-effect transistors in terms of higher source, drain, and channel resistances at high temperature operations, although further investigations on other performances such as output power and reliability are needed. The Al2O3 deposited AlGaN/GaN shows about 15% higher ns than without Al2O3 layer for the whole temperatures. On the contrary, μH at 77 K shows a slight decrease with Al2O3 deposition, which degree is not affected by the layer thickness. In the temperatures higher than 400 K, μH is almost the same for with and without Al2O3 layer.

Electronic properties of the high electron mobility Al0.56In0.44Sb/Ga0.5In0.5Sb heterostructure

Electronic properties of the Al0.56In0.44Sb/Ga0.5In0.5Sb heterostructure grown by molecular beam epitaxy are investigated. We measure by means of x-ray photoemission spectroscopy, photoluminescence, and Hall effect measurements the key parameters involved in the achievement of a high speed and very low power consumption field effect transistor: conduction and valence band offsets, energy gaps of channel and barrier materials, electron effective mass, and density of states in the channel. We observe the influence of the quantum well thickness on the electron Hall mobility and sheet carrier density. A type I heterostructure exhibiting a room temperature electron mobility of 25 000 cm2 V−1 s−1 with a sheet carrier density of 1.5×1012 cm−2 is demonstrated for the widest channel. We show that the thickness of the channel influences both Hall density and mobility through a multisubband occupancy. We discuss about the scattering mechanisms limiting the mobility in the second subband.

Effect of vacuum magnetic annealing on the structural and physical properties of the Ni and Al co-doped ZnO films

About 300 nm-thick Zn 0.87Al 0.06Ni 0.07O, Zn 0.83Al 0.06Ni 0.11O and Zn 0.81Al 0.04Ni 0.15O films were deposited on glass substrates at 300 K by co-sputtering ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h under a magnetic field of 4.8 × 10 4 A/m applied along the film plane and then were cooled down to room temperature without magnetic field. All the films have a wurtzite structure and consist of thin columnar grains perpendicular to the substrate. The annealing promotes the (002) orientation growth in the film growing direction for the Zn 0.87Al 0.06Ni 0.07O and Zn 0.83Al 0.06Ni 0.11O films as well as the (100) orientation growth for the Zn 0.81Al 0.04Ni 0.15O film. The annealing results in a slight increase in the grain size. A weak Ni diffraction peak was detected for the annealed films with high Ni content. The annealing enhances the room temperature ferromagnetism of the films. A temperature dependence of magnetization confirms that the Curie temperature is above 400 K for the annealed films. The films magnetically annealed exhibit an anisotropic magnetization behavior. The annealed Zn 0.87Al 0.06Ni 0.07O film has the lowest resistivity (8.73 × 10 −3 Ω cm), the highest free electron concentration (1.73 × 10 20 cm − 3 ) and Hall mobility (4.16 cm 2V − 1 s − 1 ). A temperature dependence of the resistivity from 50 K to 300 K reveals that the carrier transport mechanism is Mott's variable range hopping in the low temperature range and thermally activated band conduction in the high temperature range.

The effects of neutron irradiation and low temperature annealing on the electrical properties of highly doped 4H silicon carbide

The effects of neutron irradiation on the electrical properties of highly doped 4H SiC were studied. The material was fabricated into standard Hall bars for characterization of the material’s resistivity, free-carrier concentration and electron Hall mobility as a function of 1MeV equivalent neutron fluence in SiC (Φ1MeV,SiCEq). The post-irradiation effects of low temperature (175°C) annealing on the same properties were also investigated. It was found that: (1) the material’s resistivity doubled for Φ1MeV,SiCEq=2.7×1016cm−2, (2) the resistivity recovered (i.e. decreased) by only 8+1% from its post-irradiation values after 2h of annealing, (3) the carrier concentration decreased linearly with Φ1MeV,SiCEq with a carrier removal rate of ∼48.5±6.3cm−1, (4) within experimental uncertainty, the carrier concentration recovered to its pre-irradiation values after 2h of annealing, (5) the Hall mobility decreased linearly with Φ1MeV,SiCEq with a mobility damage constant of (1.49±0.2)10−19Vs and (6) the Hall mobility was further degraded (i.e. decreased) by annealing. The mobility was found to decrease from its post-irradiation value by 27±8% after 2h of annealing.

Temperature dependence of electron concentration and mobility in n-GaN measured up to 1020 K

Temperature dependence of Hall electron concentration and mobility in n-GaN has been measured up to 1020 K. The electron concentration increased monotonically with temperature and did not saturate. The measured values were fitted with the calculated ones for the whole temperature range. It is found that following two assumptions have to be made in order to obtain the best fit for both electron concentration and mobility: (i) two donor levels and one acceptor level (including dislocation) have to be taken into account; and (ii) one donor level lies in the conduction band. The obtained results in this study will contribute to the design of GaN devices operating at high temperatures.

Mobility and remote scattering in buried InGaAs quantum well channels with high-k gate oxide

The authors present results on the Hall electron mobility in buried In0.77Ga0.23As quantum well channels influenced by remote scattering due to In0.53Ga0.47As/HfO2 interface. When the top In0.53Ga0.47As/InAlAs barrier thickness was reduced from 50 to 0 nm, the mobility degraded from 12 000 to 1200 cm2/V s while the slope of its temperature dependency in the 77–300 K range changed from the conventional negative (∼T−1.2-phonon-driven mechanism) to positive (∼T). The mobility degradation is attributed primarily to remote Coulomb scattering due to the fixed charges at the semiconductor/oxide interface, as followed from the simulation results. The mobility reaches maximum at a sheet carrier density value of 2×1012 cm−2. The data indicate that passivation of InGaAs/HfO2 interface with in situ grown amorphous SiOx strongly improves mobility.