Room Temperature Hall Effect Measurements Research Articles

Improved ITO thin films with a thin ZnO buffer layer by sputtering

In this paper, we report a buffering method of improving the quality of ITO thin films on glass by r.f. magnetron sputtering. By applying a ZnO buffer before the ITO deposition in the same run of sputtering, ITO films showed single (111)-oriented highly textured structure, while ITO films showed mixed-oriented polycrystalline structure on bare glass. A design of experiment was taken out to minimize the resistivity of ITO films in the deposition parameter space (oxygen ratio, total gas pressure, and temperature). Resistance measurements showed that the ITO films with ZnO buffers had a remarkable 50% decrease of resistivity comparing to those without ZnO buffers at optimized deposition condition. Room-temperature Hall effect measurements showed that the decrease in resistivity comes from a large increase of mobility and a slight increase of carrier density after forming gas annealing. The ZnO/glass may be a good alternative substrate to bare glass for producing high quality ITO films for advanced electro-optic applications.

Synthesis and Growth of Gallium Nitride by the Chemical Vapor Reaction Process (CVRP)

A new process for synthesis and bulk crystal growth of GaN is described. GaN single crystal c-plane platelets up to 9mm by 2mm by 100μm thick have been grown by the Chemical Vapor Reaction Process (CVRP). The reaction between gallium and a nitrogen precursor is produced by sublimation of solid ammonium chloride in a carrier gas, which passes over gallium at a temperature of approximately 900°C at near atmospheric pressures. Growth rates for the platelets were 25-100 μm/hr in the hexagonal plane. Seeded growth in the c-direction was also accomplished by re-growth on previously grown c-plane platelets. The crystals were characterized by X-ray diffractometry, atomic force microscopy, secondary ion mass spectrometry, inert gas fusion, and room temperature Hall effect and resistivity measurements.

P- and N-type doping of GaN and AlGaN epitaxial layers grown by metalorganic chemical vapor deposition

Mg- and Si-doped GaN and AlGaN films were grown by metalorganic chemical vapor deposition and characterized by room-temperature photoluminescence and Hall-effect measurements. We show that the p-type carrier concentration resulting from Mg incorporation in GaN:Mg films exhibits a nonlinear dependence both on growth temperature and growth pressure. For GaN and AlGaN, n-type doping due to Si incorporation was found to be a linear function of the silane molar flow. Mg-doped GaN layers with 300K hole concentrations p ∼2×1018 cm−3 and Si-doped GaN films with electron concentrations n∼1×1019 cm−3 have been grown. N-type Al0.10Ga0.90N:Si films with resistivities as low as p ∼6.6×10−3 Ω-cm have been measured.

Growth of low resistivity p-type GaN by metal organic chemical vapour deposition

Mg-doped GaN epitaxial layers were grown on (0001) sapphire by metal organic chemical vapour deposition and were characterised by room-temperature and variable-temperature Hall-effect measurements. The authors report an in-situ Mg acceptor activation procedure which occurs in a N/sub 2/ ambient during the post-growth cool-down cycle. GaN:Mg films with a wide range of free-hole concentrations and electrical resistivities have been grown by varying the Mg precursor molar flow rate, the growth pressure, and the growth temperature. The highest 300 K free hole concentrations achieved were p/spl sime/2.2/spl times/10/sup 18/ cm/sup -3/ with mobilities /spl mu//sub p//spl sime/2.2 cm/sup 2//Vs.

Giant transversal magnetoimpedance and Hall-effect measurements in Co70.4Fe4.6Si15B10

We report room-temperature transversal magnetoimpedance (TMI) and Hall-effect measurements performed in ribbons of the zero-magnetostriction soft-ferromagnet Co70.4Fe4.6Si15B10 alloy annealed at 587 K for 15 min at a dc magnetic field of 2 kOe. The annealing showed little effect on the magnetostriction of the samples. The frequency f and the amplitude Iac of the current used in the measurements, and the measuring magnetic field H were varied in the intervals 10≤f≤105 Hz, 2.5≤Iac≤25 mA, and −15≤H≤15 kOe, respectively. The magnetic field dependence of the TMI shows a peak which is strongly dependent on f and on Iac. It reaches the giant value of 28% at H=350 Oe for f=100 kHz and Iac=25 mA. This TMI giant value is of the same order of the giant longitudinal magnetoimpedance (GLMI) but its peak is positioned in a magnetic field two orders of magnitude larger than the value obtained for the GLMI. The Hall effect yielded a value of RS=0.43 μΩ cm kOe−1. Peaks which are also frequency dependent were observed at the Hall voltage.

Hyperthermal (30–500 eV) C + ion-beam doping into GaAs during molecular beam epitaxy

Ion-beam doping of GaAs with hyperthermal (30–500 eV) carbon ion (C +) has been investigated using a combined ion beam and molecular beam epitaxy (CIBMBE) system. The CIBME system is a combination technique between a low-energy ion accelerator and a solid-source MBE, which are connected under ultra-high vacuum (UHV) condition. C +-doping was carried out during GaAs MBE growth at substrate temperature of 550°C with the same C + beam current density. Grown layers were characterized by low-temperature (2 K) photoluminescence and room temperature Hall effect measurements, and it was revealed that the incorporation behavior of C significantly depends on the acceleration energy of C + ( E C). The highest net hole concentration (∥ N A − N D∥) was obtained at E C + = 170 eV. In the energy range of E C + < 170 eV, ∥ N A − N D∥ slightly increased as E C + increased, and for E C + > 170 eV ∥ N A − N D∥ dramatically decreased with increasing E C + , which can be explained in terms of enhanced sputtering effect. On the other hand, ion-beam induced radiation damages were observed for E C + > 170 eV.

Doping-induced changes in the physical properties of In2O3:Sn films

Here we report studies carried out on heavily tin-doped and undoped indium oxide films. Structural, electronic transport and compositional properties of the sprayed films deposited with different doping levels of tin (0-110 at.% in solution), were investigated. X-ray diffraction, room-temperature Hall effect measurements, conductivity measurements at low temperatures and x-ray photoelectron spectroscopy were used for these studies. The films were polycrystalline and the preferred growth showed systematic changes with dopant incorporation from (400) to (222). The carrier mobility was very sensitive to these changes in orientation of preferred growth as well as the grain size. The high carrier concentration ( approximately 1020 cm-3) implied that the films belong to the class of degenerate semiconductors. Such a high carrier concentration was a result of increased non-stoichiometry and increased dopant incorporation. The conductivity measurements at low temperatures show that with increased Sn incorporation, electronic transport is governed by ionized impurity scattering and acoustic lattice scattering.

A study of the transition from high to low resistivity in As-grown GaAs MBE material

This work discusses the transition from high resistivity as-grown GaAs layers to thermally metastable low resistivity as-grown layers by molecular beam epitaxy. This transition occurs at about 430°C and coincides with a reflective high energy electron diffraction reconstruction change from a 2 × 1 to 2 × 4 pattern for an As4/Ga beam equivalent pressure ratio of 20. For growth temperatures in the range 350 to 430°C, room temperature Hall-effect measurements have shown resistivities of <107 ohm-cm and photoluminescence has shown new peaks at 0.747 eV and a band from 0.708 to 0.716 eV at 4.2K, in unannealed material.

Resistivity of Ru 2Si 3 single crystals

Below around 1000°C the Nowotny chimney-ladder compound Ru 2Si 3 crystallizes in orthorhombic structure (space group Pbcn). In this structure it is reported to be a semiconductor with a band gap of 0.7 eV. We obtained large single crystals of Ru 2Si 3 by a modified Czochralski pulling technique from a levitated melt in a cold Hukin type crucible. We report here resistivity measurements from 4.2 K to room temperature for current flowing along the three main crystallographic directions. The resistivity is anisotropic within the whole temperature region with ϱ a /ϱ b ≈ 2 and ϱ c /ϱ b ≈ 1.5 and is roughly constant in the whole temperature region. At room temperature and below, the conduction is extrinsic and scattering is dominated by phonons. Below 100 K freezing-out of impurity electrons gradually occurs. Below 20 K a hopping-like regime is expected but no clear evidence for a known theoretical law is obtained in a significant temperature range. At room temperature Hall effect measurement leads to positive carriers with a concentration n = 1.0 × 10 18 cm -3 and a mobility μ = 3.5 cm 2/V·s.

Molecular beam epitaxial growth of (Al,Ga)As/GaAs heterostructures and Si doping characterization study on vicinal (110) GaAs substrates

The growth of device quality (Al,Ga)As/GaAs heterostructures on [110]-oriented GaAs substrates is reported. In-situ reflection high energy electron diffration (RHEED) oscillation and ex-situ photoluminescence measurements are used to optimize the growth conditions. Si-doped GaAs epi-layers with different dopant concentrations grown at various substrate temperatures and differing As 4⧸Ga flux ratios were characterized by room temperature Hall effect measurements. It is found that silicon, as a dopant, can behave amphoterically in [110]-oriented GaAs epi-layers. By appropriately adjusting either the substrate temperature or the As 4⧸Ga flux ratio, it is possible to grow high quality n-type or p-type material using only silicon as a dopant. Up to a transition temperature of about 630°C, silicon atoms can be incorporated as donor impurities for an As 4⧸Ga flux ratio of 5. At and above this temperature, the atoms occupy lattice sites where they behave as acceptors for the same flux ratio.

Comparison of the electric properties of single-crystal and polycrystalline diamond by hall effect and capacitance-voltage measurements

The transport properties of type IIb (naturally B-doped), single-crystal diamond were investigated by differential capacitance-voltage ( C- V) measurements, Hall effect measurements and resistivity measurements. The results for the Hall effect and resistivity measurements on single-crystal samples were compared with similar measurements on polycrystalline samples grown by microwave-assisted chemical vapor deposition. The C- V and Hall effect measurements on single crystal, type IIb diamond samples showed consistent results. Temperature-dependent resistivity measurements verified an activation energy of 0.36 eV, while room temperature Hall effect measurements on a (100)-oriented, type IIb single crystal indicated that the active carrier concentration was 2.1 × 10 13 cm −3. This result was consistent with total B concentrations measured by both C- V and secondary ion mass spectroscopy (SIMS). The transport properties for polycrystalline samples were not as good as those for single-crystal samples. At room temperature, the mobilities were 3 and 10 cm 2 V −1 s −1 for two in situ doped polycrystalline thin films, as compared with 325 cm 2 V −1 s −1 for the single-crystal sample. For one in situ doped sample, the activation energy was measured to be 0.05 eV and the room temperature carrier concentration was 1.8 × 10 16 cm −3, while SIMS indicated that the total atomic B concentration was 5 × 10 18 cm −3. The relatively low carrier concentrations measured in the polycrystalline samples may be indicative of a high level of compensation (about 65%) or trapping of charge at the grain boundaries, leading to a depletion of carriers in the crystallites.

In-Situ generated arsine radicals for gallium arsenide homoepitaxy

Removed from the deposition region, an upstream hydrogen microwave plasma generates arsenic hydrides by etching the surface of solid arsenic. The hydrides are transported to the deposition region and mixed with trimethylgallium to achieve low temperature (350°-400°C) and low pressure (750 mtorr) homoepitaxial GaAs films. Low precursor V:III ratios are used to achieve homoepitaxial films with high levels of carbon dopants (l019 to mid 1020 cm−3). No active or afterglow plasma exists in the growth region. The observed homo epitaxial growth activation energies of 54 kcal/mole and 66 kcal/mole for films deposited with V:III ratios of 1:1 and 1:4, respectively, are in the range of those reported for the heterogeneous decomposition of trimethylgallium in the absence of arsine. The films are found to be of good crystalline quality via double crystal x-ray rocking curves. The majority carriers are holes and have hole concentrations that correlate to the carbon doping, as determined by room temperature Hall effect measurements and secondary ion mass spectroscopy. Carrier mobility versus carbon concentration is also presented.

P-type Conduction in Bulk ZnSe by Nitrogen Ion-Implantation

ABSTRACTP-type conduction in bulk ZnSe has been achieved using 1×1016 cm−2 nitrogen (N) ionimplantation followed by a high temperature rapid thermal annealing. Room temperature Hall effect measurements of the sample show that the hole concentration is ∼1×1017 cm−3, and the mobility is ∼30 cm2/V-s. Photoluminescence (PL) measurements were performed to study the optical behavior of the samples, and the results show that the ion implantation damage can be partially repaired by thermal annealing at 900°C or higher. Thermal degradation and recovery of the ion-implantation damage were studied as a function of the annealing temperature.

Crystal growth of CuInSe2 by the Bridgman method

Single crystals of CuInSe2 have been fabricated by the vertical Bridgman method. A conventional Czochralski crystal-pulling system was adapted for this purpose. An accelerated crucible-rotation technique was employed for a better mixing of the melt during the growth. Void- and crack-free crystal grains with an area as large as 50 mm2 and a thickness of more than 5 mm could be selectively cut from the ingots. From room-temperature Hall-effect measurements, mobility values as large as 73 cm2 ∙ V−1 ∙ s−1 were obtained for the present samples. X-ray diffraction studies suggested that abrasive polishing might create an amorphous layer on the surface of the CuInSe2 crystals.

Preparation of crystalline CuInSe 2 by directional freezing

Crystalline CuInSe 2 ingots have been prepared by a horizontal Bridgman method and a directional freezing technique. The quality of ingots grown by directional freezing technique was found to be better than that using the Bridgman method. Room temperature Hall effect measurements have been made on samples cut from as-grown ingots. The highest mobility value was 66 cm 2V -1s -1 for the p-type samples. Homojunction devices were fabricated by diffusing indium into p-type samples at a temperature of 200°C. The devices showed a photoresponse in a wavelength range from 0.5 to 1.4 μm.

The Defect Structure of Phosphorus‐Doped CdTe

Room temperature Hall effect measurements on P‐doped crystals cooled from equilibrium with atmospheres of well‐defined Cd and pressures at high temperature have made it possible to arrive at a defect model for P‐doped . Temperature dependence of the Hall effect from 77° to 335°K showed P to give rise to shallow acceptor levels at . The acceptors are probably and . The number of holes per P atom is close to one at low P contents after annealing at medium Cd pressures. The ratio decreases with increasing P concentration and by annealing at low or high cadmium pressure, indicating self‐compensation. At high the self‐compensation involves native defects . At low it involved . At high P concentrations neutral associates and are formed. The same model, with one additional constant, accounts for the solubility of phosphorus in .

The electrical properties and the magnitude of the indirect gap in the semiconducting transition metal dichalcogenide layer crystals

Room-temperature electrical resistivity and Hall effect measurements as a function of pressure are reported on p-type MoS2 and on n-type MoS2, MoSe2 and MoTe2. In each case, the resistivity decreases under pressure, due to an increase in the carrier concentration. The Hall mobility is relatively pressure-independent. The data are consistent with the predominance of extrinsic conduction in these semiconductors until well above room temperature. The impurity activation energy and its pressure dependence are given, together with estimates of the intrinsic indirect bandgap obtained from high temperature conductivity measurements, photoemission studies and band structure calculations.

Polar-Reflection Faraday Effect and the Fermi Surface ofα-Phase Silver-Magnesium and Silver-Cadmium Alloys

The Fermi surfaces of $\ensuremath{\alpha}$-phase disordered AgCd and AgMg alloys have been studied using the polar-reflection Faraday effect. Concentrations as high as 39.3-at.% Cd and 30.0-at.% Mg were obtained. It is shown that the uncertainty in the energy of states on the Fermi surface is small compared to changes which occur on alloying. Thus in both alloy systems, the Fermi surface is still a valid concept to use in discussing electronic properties of the concentrated alloys. It is found that the Fermi surfaces of both AgMg and AgCd change the same with concentration within experimental error up to 30 at.%, the maximum solubility of Mg in the $\ensuremath{\alpha}$ phase. The Fermi-surface necks continually increase in size faster than the belly dimensions with increasing Cd and Mg content. There is some evidence that the AgCd Fermi surface may have a second contact near 40-at.% Cd. By comparison with room-temperature Hall-effect measurements, it is determined that for concentrated alloys the ratio of the room-temperature relaxation time on the belly, ${\ensuremath{\tau}}_{B}$,to that on the neck, ${\ensuremath{\tau}}_{N}$, is $\frac{{\ensuremath{\tau}}_{B}}{{\ensuremath{\tau}}_{N}}=1\ifmmode\pm\else\textpm\fi{}0.2$ for both AgMg and AgCd. In spite of the similarities of the Fermi surfaces for both AgMg and AgCd, only AgCd satisfies the Hume-Rothery rules. This is the first experimental evidence that the simple explanation that the Hume-Rothery rules depend only on Fermi-surface properties of the $\ensuremath{\alpha}$ phase is inadequate.

Impurity Compensation and Magnetoresistance in p-Type Silicon

A new method is proposed for determining the separate concentrations of acceptor and donor impurities in crystals of p-type silicon, and thereby the degree of compensation of acceptors by donors. The method involves finding the total concentration of impurities in a sample from a measurement of the weak-field transverse magnetoresistance at 77°K and combining this result with the excess of acceptors over donors determined from a room-temperature resistivity or Hall effect measurement. An empirical ``master curve'' of magnetoresistance vs impurity density has been constructed for this purpose. The impurity densities for the master curve were measured by the usual method of fitting a theoretical carrier concentration vs temperature equation to an experimental curve obtained from Hall effect data.