High Hall Mobility Research Articles

Micrograin structure influence on electrical characteristics of sputtered indium tin oxide films

The relationship between micrograin structures and electrical characteristics of sputtered indium tin oxide (ITO) films was investigated. Micrograin structures were observed by a high resolution scanning electron microscope. Electrical characteristics were evaluated by four point probe resistance measurement and Hall effect measurement. Low resistivity ITO films had domain structures. One domain consisted of many sputter grains having the same orientation. The resistivity decreased with increasing domain size. The domain boundary might cause scattering for conduction electrons. Therefore, larger domain ITO films had a higher Hall mobility. The minimum resistivity was 1.8×10−4 Ω cm, deposited at a sputtering voltage of −250 V and a 250 °C deposition temperature. The electron conduction mechanism in domain structured ITO films was taken into consideration.

Hall mobility and temperature dependent photoluminescence of carbon-doped GaAs

We have analyzed Hall mobilities and photoluminescence (PL) spectra of carbon(C)-doped GaAs epilayers as a function of hole concentration and temperature. We have obtained an empirical relation of hole concentration dependent Hall mobility appropriate for C-doped GaAs which have higher Hall mobilities than Zn-doped GaAs. By PL measurement, temperature dependence of band gap energy E g and PL peak energy E M shift of C-doped GaAs with a hole concentration of 9.2 × 10 19 cm -3 have been measured. The resulting E g and E M at 0 K are (1.420 ± 0.003) eV and (1.458 ± 0.003) eV, respectively. The PL peak energy of C-doped GaAs with hole concentrations varying from 1 × 10 17 to 9.2 × 10 19 cm -3 have been measured and compared with previously reported data.

Si/SiGe modulation-doped structures with thin buffer layers: Effect of substrate orientation

High quality Si (strained)/Si0.7Ge0.3 (relaxed) modulation-doped structures incorporating unusually thin (700 nm) buffer layers were grown with molecular beam epitaxy at 700 °C. By utilizing (100) substrates misoriented toward (011) by 4°, the density of threading dislocations was reduced by over an order of magnitude as compared with conventional techniques. These layers produced exceptionally high Hall mobilities of 1790 cm2/V s at 300 K and 19 000 cm2/V s at 77 K on n-type modulation-doped heterostructures. The effect of substrate misorientation on threading dislocation density was investigated using transmission electron microscopy and Nomarski microscopy.

Carbon incorporation during growth of GaAs by TEGa-AsH3 base low-pressure metalorganic chemical vapor deposition

Heavily carbon-doped GaAs (1×1018∼1×1020 cm−3) grown by low-pressure metalorganic chemical vapor deposition using triethylgallium and arsine as sources and liquid carbon-tetrachloride (CCl4) as dopant has been investigated. The carrier concentration was verified at various growth temperatures, V/III ratios, and CCl4 flow rates. Dopant concentration first increased from 550 °C and reached a maximum at 570 °C growth temperature (Tg) and then decreased monotonously. Carbon incorporation was strongly enhanced when the V/III ratio was less than 30 at Tg=590 °C or less than 40 at Tg=630 °C. Hole concentration increased and then decreased as CCl4 flow rate increased. Growth rate of layers decreased as growth temperature and flow rate of CCl4 increased. The doping efficiency of epitaxial layers grown on the (100) substrate was higher than that on the 2° off toward <110≳ misoriented substrate. Carbon-doped GaAs films had higher Hall mobility than zinc-doped GaAs films at high doping levels due to less self-compensation. The highest dopant concentration in this system was 2.3×1020 cm−3 at Tg=580 °C and V/III=10.

Optimization of modulation-doped Ga1−xInxAs/InP heterostructures towards extremely high mobilities

This paper presents a study of the electrical and structural properties of inverted modulation-doped GaInAs/InP heterostructures grown by low-pressure metalorganic vapor phase epitaxy. First, the thickness of the GaInAs layer was optimized in lattice-matched samples to find the smallest thickness in which high Hall mobility is observed. Next, in a section closest to the InP the In content was varied. A steady increase of mobility with indium composition was observed. A maximum of 450 000 and 15 500 cm2/V s was obtained for a 10-nm-thick Ga1−xInxAs layer with x=0.77 at 6 and 300 K, respectively. Channels with higher indium content exceed the critical thickness and mobility drops off sharply. The decreasing mobility correlates with the formation of misfit dislocations at the interface indicating increasing scattering processes of the GaInAs layer.

Electronic-transport properties of unhydrogenated amorphous gallium arsenide

Hall mobility, μH, and electrical conductivity, σ, of unhydrogenated amorphous-gallium-arsenide films, prepared by r.f. sputtering, have been measured. Conductivity as a function of temperature shows a variable-range hopping mechanism atT<260 K, while at high temperature, conductivity and Hall mobility are both thermally activated. The results are interpreted in terms of the presence of defect complexes due to an excess of Ga. The stoichiometry and the structure of the films are used to explain the behaviour and the values of μH. The values of the activation energy of the conductivity seem in agreement with theoretical calculations on the position of electronic states created by defect complexes in the mobility-gap of a-GaAs.

Electric and magnetic field dependence of the conductivity in poly(3-hexylthiophene langmuir-blodgett films

The conductivity of undoped and NOPF 6-doped Langmuir-Blodgett thin films of poly(3-hexylthiophene) has been studied under strong electric (up to 60 kV/cm) and magnetic (up to 15 T) fields at low temperatures (down to 4.3 K). The electric-field dependence of the conductivity in doped films fits the theory of charging-energy-limited tunneling between highly conducting regions. In the electric-field-induced conduction mode, the magnetoresistance adopts a positive B 2 dependence which is argued to arise from the geometrical contribution corresponding to an extremely high and bias-dependent Hall mobility, over 10 3 cm 2/Vs below 40 K. However, the high Hall mobility was not measurable using a conventional four-point technique. The results can be reproduced in free-standing films of doped poly(3-hexylthiophene). Undoped Langmuir-Blodgett films show a linearly varying positive magnetoresistance the magnitude of which increases with decreasing temperature.

Growth Morphology of InN Thin Films by Scanning Tunneling and Atomic Force Microscopies and X-Ray Scattering

AbsiractThe evolution of the growth morphology of thin films of InN on (00.1) sapphire and on (00.1) sapphire prenudeated by a layer of AIN have been followed as a function of the thickness of the InN overlayer. The InN thin films and the AIN nucleation layers were deposited by reactive magnetron sputtering and first characterized by X-ray scattering, profilometry, and electrical transport. These AIN-nucleated InN films displayed heteroepitaxial grains, and high Hall mobility -even in the limit of InN overlayer on the order of 20-40Å. In parallel, InN films of varying thickness were grown directly onto (00.1) sapphire. These films showed a mixture of textured and heteroepitaxial grains, and lower Hall mobility. Atomic force and scanning tunneling microscopy studies have focussed on the morphology of the InN films with thicknesses: (a) much smaller than the AIN nucleation layer; and, (b) near the morphological transition that occurs at ∼1μm and has been attributed to the crossover from a 2D to a 3D growth mechanism. Additional correlations of X-ray structural coherence with growth mode are also examined.

Investigation of Carbon Incorporation into GaAs by TEGa-AsH3 Based Low Pressure Metalorganic Chemical Vapor Deposition

ABSTRACTHeavily Carbon doped GaAs(l×1018−1×1020cm−3 ) grown by low pressure metalorganic chemical vapor deposition(LPMOCVD) using triethylgallium(TEGa), arsine(AsH3) as sources and liquid carbon-tetrachoride(CCI4) as dopant has been investigated. The carrier concentration was verified at various growth temperatures, V/III ratios and CCI4 flow rates. Dopant concentration first increased from 550°C and reached a maxium at 570°C and then decreased monotonously. Carbon incorporation was strongly enhanced when V/III ratio was less than 30 at Tg=590°C or less than 40 at Tg=630°C. Hole concentration increased and then decreased as CCI4 increased. The doping efficiency of epitaxtial layers grown on(100) substrate was higher than that on 2° off toward &lt;110&gt; misoriented substrate. Carbon doped GaAs films had higher Hall mobility than zinc doped GaAs films at high doping level due to less self-compensation. The highest dopant concentration in this system was 2.3×1020cm−3 at Tg=580°C and V/III=10.

Magnetotransport studies of remote doped Si/Si 1− xGe x heterostructures grown on relaxed SiGe buffer layers

n-Type modulation-doped Si/Si 1− x Ge x single heterostructures grown on relaxed Si 1− x Ge x buffer layers with extremely high Hall mobilities are investigated by Hall and Shubnikov-de Haas measurements. For samples grown on thick buffers with linearly increasing germanium contents we find the single-particle relaxation time τ s to be about an order of magnitude smaller than the transport relaxation time τ t which indicates that long-range scattering is the dominant scattering mechanism in these heterostructures. At intermediate magnetic fields both the spin and the remaining twofold valley degeneracies of the strained silicon channels are lifted. The quality of these samples is further illustrated by well-defined quantum Hall plateaux accompanied by vanishing longitudinal resistivities at integer filling factors.

Molecular-beam epitaxial growth of p- and n-type ZnSe homoepitaxial layers

Undoped, p- and n-type ZnSe homoepitaxial layers have been successfully grown by molecular beam epitaxy on dry-etched substrates. ZnSe substrates were etched with a BCl 3 plasma to eliminate polishing damage. The full width at half maximum of an X-ray rocking curve for a homoepitaxial layer has reached 21 arc sec. N-doped ZnSe homoepitaxial layers grown with the active-nitrogen doping technique have shown p-type conduction which is the evidence of p-type conduction in ZnSe. The n-type homoepitaxial layers have been grown with Cl doping. The Cl-doped homoepitaxial layers have shown high Hall mobilities relative to heteroepitaxial layers. These undoped, N-doped and Cl-doped layers have exhibited strain-free photoluminescence properties; free exciton emission, neutral acceptor-bound exciton emission and neutral donor-bound exciton emission showed a single peaks at 2.804, 2.7931 and 2.7980 eV, respectively.

Growth Dependence of Thickness, Morphology and Electrical Transport of InN Over Layers on Ain-Nucleated (00.1) Sapphire

ABSTRACTThe seeded-heteroepitaxial growth, morphology and electrical transport properties of InN overlayers deposited by reactive magnetron sputtering on AIN-nucleated (00.1) sapphire have been investigated. For comparison, InN films were grown directly onto (00.1) sapphire under identical experimental conditions. These unseeded films showed a unimodal growth and were a mixture of textured and broadly heteroepitaxial grains. Low Hall mobility and carrier concentration and high resistivity were typical. In contrast, the AIN-nucleated InN overlayers exhibited a bimodal growth, strongly heteroepitaxial grains, and high Hall mobility. A particularly interesting aspect of the films grown on seeded (00.1) sapphire is the preservation of electrical continuity and high Hall mobility even in the limit of InN overlayers with thicknesses only on the order of 20–40Å.

Zinc and tellurium doping in GaAs and Al xGa 1− xAs grown by MOCVD

Diethylzinc and diethyltellurium have been used as p-type and n-type dopants, respectively, for GaAs and Al x Ga 1 - x As epilayers grown by low-pressure metalorganic chemical vapor deposition. The influence of growth temperature, growth rate, and dopant mole fraction upon carrier concentration were investigated for both dopants under similar growth conditions. The V/III ratio was 50 for all the samples. It was observed that the growth parameters do not affect the mobility of doped samples for a given carrier concentration. For both Zn and Te doped layers, the carrier concentrations increased linearly with decreasing growth temperature and increasing mole fraction. For the undoped samples, higher growth rates resulted in lower background impurity incorporation and higher Hall mobilities. The Te incorporation increased with increasing growth rate; however, the Zn incorporation was reduced under similar conditions. The morphology of heavily-doped samples was found to be dependent upon growth temperature and growth rate. By varying these two parameters, mirror-smooth surface morphology was obtained for Zn-doped GaAs epilayers of 1 × 10 20 cm -3 and Te-doped GaAs epilayers of 1 × 10 19 cm -3.

Polycrystalline silicon carbide films deposited by low-power radio-frequency plasma decomposition of SiF4-CF4-H2 gas mixtures

Polycrystalline silicon carbide thin films have been deposited on amorphous substrates by radio-frequency plasma-assisted decomposition of tetrafluoro silane, tetrafluoro methane, and hydrogen gas mixtures using low-power density and deposition temperatures. The material is shown to possess the α-SiC structure using transmission electron microscopy. It has highly visible transmittance and exhibits bands due to silicon carbide as well as fluorine bonded to carbon and silicon in the infrared transmission spectra. It is easily doped, both types showing high conductivity (∼10 S/cm) and Hall mobility [∼10 cm2/(V s)] for either carrier type. The conductivity is seen to be independent of thickness down to ∼10 nm when deposited on glass. This behavior and the dependence of both structural and electronic properties on deposition parameters is discussed in terms of the chemical reactions in gas phase and on the growth surface.

Thickness Dependence of Electrical and Structural Properties of FTO Films

AbstractFluorine (0.8 M) doped tin oxide films of various thicknesses were prepared on heated glass substrates (520 °C) by spray pyrolysis technique. The chemical and thermal stabilities of FTO films were found to be very good. The characterization has been done by XRD and found to agree with the reported results. As thickness of the film increases, intensities of peaks increased. From the X‐ray diffraction data, grain size of the crystallites have been calculated. The electrical and structural properties were studied for different thicknesses. Hall measurements showed that thicker films have relatively high Hall mobilities compared to those of thinner films. The high carrier concentration showed that the films are degenerate. The relationship between carrier concentration and Hall mobility revealed that the ionized impurity scattering centres were the dominant cause of scattering.

Transport properties of flash-evaporated ( Bi1 − xSbx) 2Te3 films I: Optimization of film properties

Bi 0.5Sb 1.5Te 3 films were deposited by flash evaporation on silicon wafers with thermally grown SiO 2 overlayers (SiO 2/Si substrates). Their transport properties, i.e. the electrical conductivity, Hall coefficient, magnetoresistance coefficient, Hall mobility, Seebeck coefficient, thermal conductivity and thermoelectric figure of merit, were determined in the temperature range from 80 to 400 K. Investigations concerning the annealing behaviour in an argon atmosphere were carried out on films without and with protective layers. By optimization of manufacturing conditions, it was possible to obtain films of a high Hall mobility and with a thermoelectric figure z of merit of 2.9 × 10 −3 K −1 at room temperature. Since photolithographic structurization is possible these films will be useful as p-type materials for many applications in thermoelectric thin film devices in combination with microelectronic circuits on SiO 2/Si wafers.

LPE crystal growth and magnetophonon resonance recombination of Hg1-x-yCdxMnyTe

Hg1-x-yCdxMnyTe crystals have been successfully grown on CdTe substrates for the first time by the LPE method from Hg-rich solutions (x<or=0.4, y<or=0.1). LPE layers exhibit high electron Hall mobilities and excellent compositional uniformity both in the plane and along the growth direction. Such a fact has not been reported for Hg1-xCdxTe. Using the high-quality crystals grown by this method, a new type of magnetophonon effect associated with a recombination process with the emission of two TA phonons was studied in Hg1-x-yCdxMnyTe. From the analysis of experimental results of magnetophonon resonance (MPR) recombination, the band parameters near the band edge are determined precisely. Furthermore, the MPR recombination transitions associated with the impurity level were also detected. An energy gap dependence of the resonant acceptor state has been deduced for a wide range of zero-gap regions.

Characteristics of carbon incorporation in GaAs grown by gas source molecular beam epitaxy

Nominally undoped p-type GaAs has been grown by gas source molecular beam epitaxy (GSMBE) using triethygallium and arsine. The temperature dependence of carbon incorporation has been investigated. It has been found that there exists an optimum growth temperature (Tg) of about 550 ° C, at which the lowest carbon incorporation and the highest Hall mobility are attained. At Tg higher than 550 ° C with a V/III ratio of 5, the carrier concentration exhibits an Arrhenius type dependence on Tg with an activation energy of 2.2 eV. In contrast, when Tg is lower than 550 ° C, the carrier concentration increases with decreasing Tg. Defect induced bound exciton peaks have been observed in the photoluminescence spectra except for the sample grown at the optimum growth temperature. A qualitative model to explain the characteristics of carbon incorporation will be discussed.

Low-temperature highly preferred polycrystalline Si film growth on crystallized amorphous Si by reactive ion beam deposition

Highly preferred polycrystalline Si (polysilicon) film growth on amorphous Si with ion‐assisted crystallization by reactive ion beam deposition (RIBD) at the low temperature of 550 °C was investigated. This method uses low‐energy controlled ionized species produced from electron‐cyclotron‐resonance plasma. To achieve highly preferred polysilicon film growth, a new growth process using ion‐assisted crystallization was developed as follows: After a thin amorphous Si film was deposited on an amorphous substrate at 100–150 °C and 100 eV by RIBD using SiH4, it was crystallized at 550 °C by 400‐eV H+ and H+2 irradiation using the same RIBD system. Then, a polysilicon film was grown at the same temperature and 100 eV by RIBD using SiH4. Polysilicon films grown by this process possess stronger Si(220)‐preferred growth orientation and higher Hall mobility than the films grown directly on amorphous substrates.

Dependence of GaAs-AlxGa1−xAs heterostructures on Al composition for metal-semiconductor field-effect transistor operation

High-quality GaAs-AlxGa1−xAs heterostructures for metal-semiconductor field-effect transistor (MESFET) applications have been grown by metalorganic vapor-phase epitaxy. High electron Hall mobility of up to 4000 cm2/(V s) for a carrier concentration of 3.5×1017 cm−3 was obtained for Si-doped GaAs grown on AlxGa1−xAs. It was learned that the electron Hall mobility of GaAs is not dependent on the Al composition of the AlxGa1−xAs buffer layer for 0≤x≤0.8. Good drain current-voltage saturation characteristics were observed for GaAs MESFETs with a 0.3-μm gate length and AlxGa1−xAs buffer layers. At drain voltages below 3 V, the drain conductance was at its lowest for Al composition around x=0.6. However, an anomalous peak in the drain conductance was observed at drain voltages of 3–6 V and at Al compositions of x=0.6 and 0.8. Drain conductance also increased as x did for x≥0.45 when measured at a microwave frequency. These phenomena can be understood by considering electron injection into the buffer/substrate region from the GaAs channel. The amount of this injection coincided well with the reduction in the conduction-band energy barrier at the GaAs-AlxGa1−xAs heterointerface for x&amp;gt;0.45 for electron transport.