Microwave Hall Research Articles

Microwave Hall effect measurement for materials in the skin depth region

We developed a new microwave Hall effect measurement method for materials in the skin depth region at low temperatures using a cross-shaped bimodal cavity. We analytically calculated electromagnetic fields in the cross-shaped cavity and the response of the cavity including the sample, whose property is represented by the surface impedance tensor; furthermore, we constructed the method to obtain the Hall component of the surface impedance tensor in terms of the change in resonance characteristics. To confirm the validity of the new method, we applied our method to measure the Hall effect in metallic Bi single crystals at low temperatures, and we confirmed that the microwave Hall angles coincide with the DC Hall angle. Thus, it becomes clear that the Hall angle measurement under cryogenic conditions becomes possible without any complicated tuning mechanisms, and our bimodal cavity method can be used to measure the microwave Hall effect on materials in the skin depth region. The result opens a new approach to discuss the Hall effect in condensed matter physics such as the microwave flux-flow Hall effect in superconductors.

Effects of oxygen related thermal donors on the performance of silicon heterojunction solar cells

Absract The influence of oxygen-related thermal donors (TDs) on the performance of silicon heterojunction (SHJ) solar cells was explored experimentally in this paper. It is found that a certain number of thermal donors could do much harm to the performance of SHJ solar cells. The efficiency of SHJ solar cells is usually reduced by a value of ~ 1% absolute in the case of thermal donors with a concentration of nearly 1015 cm−3. The microwave photoconductance decay and Hall Effect studies have proved that the TDs can significantly reduce the carrier lifetime of n-type silicon substrate, but have no influence on the carrier mobility. Deep level transient spectroscopy (DLTS) measurements have further demonstrated that the TDs cause an energy level at Ec-0.13 eV with carrier capture cross-section of 10−15 cm2, which is responsible for the reduction of carrier lifetime and solar cell efficiency.

The microwave Hall effect measured using a waveguide tee

This paper describes a simple microwave apparatus to measure the Hall effect in semiconductor wafers. The advantage of this technique is that it does not require contacts on the sample or the use of a resonant cavity. Our method consists of placing the semiconductor wafer into a slot cut in an X-band (8–12 GHz) waveguide series tee, injecting microwave power into the two opposite arms of the tee, and measuring the microwave output at the third arm. A magnetic field applied perpendicular to the wafer gives a microwave Hall signal that is linear in the magnetic field and which reverses phase when the magnetic field is reversed. The microwave Hall signal is proportional to the semiconductor mobility, which we compare for calibration purposes with d.c. mobility measurements obtained using the van der Pauw method. We obtain the resistivity by measuring the microwave reflection coefficient of the sample. This paper presents data for silicon and germanium samples doped with boron or phosphorus. The measured mobilities ranged from 270 to 3000 cm2/(V s).

The MTT-S Historical Collection [MTT World

The at the 2014 International Microwave Symposium (IMS2014) in Tampa, Florida, USA, marked the 35th anniversary of the IEEE Microwave Theory and Techniques Society (MTT-S) Historical Collection. The collection was started and first displayed at IMS1980 in Washington, D.C. According to a report by Ted Saad: At the 15 January 1980 MTT-S Administrative Committee (AdCom) meeting in Washington, D.C., Dr. Steve Adam, the then AdCom president, gave me the task of preparing a historical exhibit for the 1980 MTT-S Symposium to be held in Washington on 28–30 May 1980. No specifications or instructions were given. The was an outgrowth of a suggestion on the part of Dr. John Horton, who for several years had proposed some type of microwave hall of fame. The collection has grown steadily over the years and now consists of more than 1000 cataloged items. At the end of 2014, there were 522 pieces of hardware, 328 books, 196 miscellaneous documents, and 14 videos. The hardware artifacts comprise; 353 tubes, including gridded types, klystrons, magnetrons and other crossed-field types, radar transmit‐ receive (T/R) tubes, and tube components; 76 subassemblies or modules, including amplifiers, oscillators, and various test equipment; 56 transmission line items, including couplers, slotted lines, variable attenuators, phase shifters, and filters; 37 individual solid-state components. Some of the artifacts are one-of-akind experimental pieces like the copper- foil-lined wooden block that was used as a waveguide coupler. Many are samples of mass quantities taken from the production line. The oldest truly microwave items are two 1932 splitanode magnetrons from Ross Kilgore of Westinghouse. The newest is a 1996 Litton mini traveling-wave tube (TWT). The books include engineering texts such as a complete 28-volume set of the MIT Radiation Laboratory (Rad Lab) series, biographies of various individuals, company histories, and manufacturers' catalogs.

Microwave Hall mobility and electrical properties of electrospun polymer nanofibers

Composite nanofibers from poly(methylmethacrylate)- (PMMA-) conducting polyaniline [PANI(HCl)] were prepared by using the electrospinning technique. The morphology and structural details of the fibers were characterized by SEM and the ac conductivity of the composite fibers found was measured to be ∼ 2.17×10−4 S/cm which is very good enhancement compared to that of pure PMMA and conductivity of PANI-PMMA thin films as well. The conductivity is found to increase with increase in the polyaniline content in the composite. Microwave Hall mobility measurements on electrospun nanofibers showed 17 cm2/V s for the lower loadings. With further increase in the polyaniline content in the composite, the mobility value decreases which is attributed to the increase in carrier-carrier scatterings.

Effet Hall Hyperfréquence Dans Des Semi-Conducteurs Constituant Des Jonctions

The resonances at microwave frequencies can be observed in polarized junctions; this was studied in previous papers and we have called for an important contribution of minority carriers. With a magnetic field B, a non diagonal component of the electrical conductivity can exist, a sort of microwave Hall effect. This can be considered as the effect of the non-diagonal part of the microwave susceptibility along the E ⁁ B direction. We report the observation of this non-diagonal component, which allows to verify the sign of the charge carriers. This experiment can be considered as a generalization of the d.c. Hall effect.

Microwave hall effect measurements on biopolymers

A 33-GHz microwave Hall effect detection system is described which is capable of measuring charge carrier mobility values larger than about 3 × 10-5 m2/V sec. An important advantage of this electrodeless technique for measurements on biological materials is that macroscopic defects do not mask the desired microscopic electronic properties. For several polypeptides and protein samples the results are consistent with a conduction mechanism involving the hopping or tunneling of charge carriers between localized energy states. However, for collagen-methylglyoxal samples a relatively large p-type Hall effect has been observed which not only indicates the possibility of conduction in a band of extended states, but also gives strong support to the concept that methylglyoxal can act as an electron acceptor in charge-transfer interactions with protein molecules.

Electronic properties of protein-methylglyoxal complexes: Strong evidence for energy-band conduction

Various measurements, including piezoelectric, hydration isotherm, microwave Hall effect, steady-state conduction, and dielectric properties over the effective frequency range 10−5 to 1010 Hz, are reported for several protein samples that have been complexed with methylglyoxal. The extent of the binding of methylglyoxal has been established using C14 labeled methylglyoxal and scintillation counting measurements. Compared with the normal proteins, the brown complexed proteins exhibit a marked increase in electronic conductivity, free-electron spin density, and piezoelectric response. Unlike the untreated proteins, the protein complexes also exhibit a distinct low-frequency dielectric dispersion and at 10 GHz there is a reversal of the usual electric-field saturation of polarizability. Compared with normal casein, the casein complex exhibits an increase in the monolayer hydration capacity. These effects can be taken as evidence that when methylglyoxal is incorporated into the structure of a protein molecule, a charge-transfer interaction occurs resulting in the creation of mobile electron “holes.” This, in turn, satisfies the basic prerequisite for the applicability of Szent-Gyorgyi's electronic theory of the “living state” and of cancer.

Microwave Hall mobility studies on polymer-single walled carbon nanotube composite fibers

Composite fibers of single walled carbon nanotubes dispersed in poly(methyl methacrylate) and polystyrene are prepared using electrospinning. The single fiber electrical conductivity is measured as a function of the composition of carbon nanotubes. A noncontact method of measuring the carrier mobility at microwave frequency (14GHz) using bimodal cavity is employed. The mobility measurements indicate lower percolation threshold for mobility compared to electrical conduction. For higher concentrations of carbon nanotubes, the mobility is found to decrease indicating possible carrier-lattice scattering.

Microwave hall mobility studies on polymer–metal oxide nanocomposites

AbstractFilms of polymer metal oxide composites with poly(methyl methacrylate) and metallic powders (CuO, Ni, and brushed Fe3O4) were prepared with a spin‐casting method. Electric transport studies indicated that the compositions surpassed the percolation threshold limit. Alternating current (AC) conductivity studies confirmed a hopping mechanism with power‐law behavior in frequency. For the first time, the mobility values of the carriers in these films were measured by the contactless microwave Hall effect technique with a bimodal cavity operating at 14 GHz. In this technique, a circular bimodal cavity is used to measure the change in the transmission coefficient (proportional to the carrier mobility) due to the application of a static magnetic field perpendicular to the microwave electric fields. The mobility measurements indicated a decrease in mobility with increasing quantity of CuO and Ni and showed an increase in the carrier–lattice scattering, whereas the mobility increased with increasing Fe3O4 due to the negative magneto resistance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Analysis of Bimodal Cavities for Microwave Hall Effect Measurements

In the field of non-contact methodology for the evaluation of carrier transport study, microwave Hall mobility technique using bimodal cavity is the most sensitive method available so far. Though there is no constraint for the use of different types or shapes of the bimodal cavities used, each cavity would have its own advantages and disadvantages. In this respect, it is very important to analyze the sensitivity of different cavities that could be used in this methodology. In this paper, different bimodal cavities [TE112 (X-band) cylindrical and TE111 (P-band) cylindrical, TE101 (X-band) cubical and a rectangular bimodal cavity (X-band resonating with TE103 and TE105 modes)] are used to evaluate the carrier mobility in various semiconductor samples. These cavities are then analyzed in terms of the sensitivity and the percentage of deviation from the DC mobility values.

New approach for measuring the microwave Hall mobility of semiconductors

Measurement of Hall mobility in semiconductor samples using bimodal cavity method gives distinct advantages due to noncontact nature as well as the provision to measure anisotropic mobility. But the measurement approaches followed till now have a disadvantage of having high error values primarily due to the problem in evaluating the calibration constant of the whole experimental arrangement. This article brings out a new approach that removes such disadvantage and presents the calibration constant with 1% accuracy. The overall error in the carrier mobility values is within 5%.

Microwave Hall effect measurements on biological and organic semiconductors

Microwave Hall effect measurements have been performed by improved 10 GHz bimodal cavity resonators with hybrid end walls used to avoid the background signal that obscures the measurements on low mobility materials. Hall mobility results on copper phthalocyanines CuPc and other organic semiconductors, in the range of 8 cm2/V s to 60 cm2/V s, provide evidence of acoustic phonon scattering as the dominant conduction mechanism. Presently, the microwave Hall effect seems to represent the only means available for quantitative measurements on biological substances like DNA and proteins, which yield mobility values lower than 10 cm2/V s, and are therefore consistent with conduction mechanism involving hopping of charge carriers between localized energy sites.

Measurement of the microwave Hall effect for the characterization of semiconductors

Microwave Hall experiments in a bimodal cavity are presented. The principle of the measurements is elucidated and the experimental set-up is considered. A quantitative evaluation of the measurement data is given. Precise cavity tuning with the help of a rotating sample holder is discussed. Results of measurements on crystalline silicon and pyrite (FeS 2) are shown.

Improved microwave Hall effect measurements method

Measurements of the microwave Hall mobility of semiconductors have been performed by an improved contactless method at 20 GHz by using a bimodal cavity resonator and a two-channel vector network analyzer. Data analysis was performed by using generalized expressions for the mobility, taking into account different coupling values on the two ports and a nonlinear response due to high magnetic fields in samples with mobility from thousands of cm2/V s. For several samples, Hall microwave and dc measurements have been compared, confirming the reliability of the proposed method; the characterization of bulk n-ZnSe and modulation-doped n-Al0.33Ga0.67As/GaAs two-dimensional electron gas samples is in particular presented. This method appears particularly suitable for the experimental determination of magnetotransport properties of semiconductor materials, especially when good electric contacts are difficult to be realized.

Transport mechanisms in hydrogenated microcrystalline silicon

Transport properties of microcrystalline (μc-Si/H) and polycrystalline (p-Si) silicon films are analyzed by time resolved microwave conductivity (TRMC), diffusion-induced TRMC (DTRMC), and Hall measurements. The comparison of carrier mobilities in microcrystalline silicon determined by TRMC as well as DTRMC shows that trapping in the disordered part of these films is not the main limiting parameter for transport in microcrystalline silicon. Besides, it is demonstrated that TRMC measurements are not sensitive to barriers between the crystallites. Our measurements reveal that, contrary to the case of p-Si, the influence of barriers in μc-Si/H can be neglected. Transport in μc-Si/H is consequently mainly limited by defects inside the crystallites.

Microwave dielectric constant of small samples: application to RNiO 3 perovskites

We have developed a technique to measure the dielectric constant of small quantities of compounds (a few milligrams) at microwave frequencies. When the dielectric constant ϵ r is greater than 1, the electric field is greatly modified inside the sample. The results have allowed us to overcome this problem when it is necessary to know the electric field in order to exploit further measurements such as conductivity or microwave Hall effect measurements. As proof of the validity of our results on the value of the electric microwave field, we have calculated the frequency shift for small samples in a microwave cavity. We have used classical results on the energy stored in a microwave cavity, but with some corrections for which we have considered the corresponding elements between a microwave cavity and a low frequency circuit. We have also made a proposal for a new method for measuring ϵ for very small samples (typically 1/100 mm 3) using gallery mode cavities. We have given original results for ϵ in perovskites Sm 1− x Nd x NiO 3 and some other components.

Study of electrical transport properties of fine magnetic particles using microwave Hall effect techniques

Microwave Hall effect (MHE) techniques, combined with the resonant perturbation method, can be used to study the electrical transport properties of fine magnetic particles. In our study, an X band TE112 bimodal cylindrical cavity is built and a vector network analyzer (HP8719C) is used to conduct microwave measurements. From the change of the quality factor before and after the introduction of magnetic particles, the conductivity of the particles can be obtained. From the change in power transmission between the two orthogonal degenerate modes of the bimodal cavity before and after the application of a static magnetic field, the mobility of carriers in the particles can be obtained. The sign of the carriers can be determined by calibration or by introducing a small imbalance into the cavity. The Hall mobility of fine magnetic particles can be deduced after the saturation level of the magnetization is technically achieved. Results show that the mobility and conductivity of Fe/sub 3/O/sub 4/ fine particles are much larger than those of /spl alpha/-Fe/sub 2/O/sub 3/ fine particles. The sign of the charge carriers in Fe/sub 3/O/sub 4/ fine particles is found to be negative, while the charge carriers in /spl alpha/-Fe/sub 2/O/sub 3/ fine particles show a positive sign.

Microwave hall field inertia due to dielectric relaxation time

The magnetoresistive e.m.f. caused by microwave was measured as a function ofωτm in wide (3 cm – 4mm) range wave length. It has been found that Maxwell relaxation time does not influence the microwave Hall field lag in semiconductors. The discussion of these results is presented.

Studies of Gas Adsorption on ZnO Using ESR, FTIR Spectroscopy, and MHE (Microwave Hall Effect) Measurements

This paper describes the application of a new technique-Microwave Hall Effect (MHE) measurements-to measure electron mobilities and to determine the effect of adsorption on electron densities of powders. Conduction electron densities calculated from microwave measurements of both mobilities and conductivities, as well as ESR spectroscopy and chemisorption measurements, have been applied to characterize high-surface-area ZnO (up to 30 m2/g) samples before and after exposure to O2, CO2, CO, and H2. Evacuation at 673 K removed lattice oxygen to produce paramagnetic lattice vacancies, (V+0)− and an approximately equal number of conduction electrons, e−. Adsorption of O2 decreased both species and created an O−2 species, but a larger quantity of O2 also adsorbed and appeared to reoxidize the surface and remove neutral V0 sites. Reversible CO adsorption occurred which had little effect on (V+0)− and e−; however, CO adsorption on an oxygen-precovered surface reestablished (V+0)− and e− species and decreased the O−2 species. After this step, very weak carbonate bands were observed using DRIFTS. CO2 adsorption on ZnO after evacuation at 673 K decreased the e− and (V+0)− concentrations equally, while much smaller decreases of each species occurred after CO2 adsorption on an oxygen-precovered surface, although O−2 species were unaffected. This showed that CO2 does not react with adsorbed O−2 species, but can interact with both (V+0)− and conduction electrons at sites not covered by molecular oxygen.