Hall Effect Mobility Research Articles

Bias Stress Measurements on High Performance AlGaN/GaN HFET Devices

High performance AlGaN/GaN heterojunction field effect transistor (HFET) devices have been fabricated, using material grown by MBE on sapphire substrates. The Hall effect 2DEG sheet charge densities and mobilities were as high as 1.68 × 10 13 cm -2 and 1000 cm 2 /Vs respectively. Peak dc currents in excess of 1 A/mm, with transconductances in excess of 220 mS/mm were common. f T and f max scaled linearly with the inverse of the gate length, with maximum values of 39 and 80 GHz recorded for T-gates of length 0.3 μm. The devices with optically defined gates were stressed at V DS = 10 V and V G = 1 V. for times up to 5000 s. The stress decreased both f T and f max , but this degradation mostly recovered after a few days. In contrast, the gate leakage current improved (decreased) with stressing, but did not return to the initial undesirable levels. Thus, we found that electrical bias stressing can have a positive effect on some of the characteristics of our devices.

Transport properties of n-type CuGaSe 2

Hall effect, electrical conductivity, and charge carrier mobility of n-type CuGaSe 2 single crystals are studied in the temperature range between 2 and 300 K. The experimental data, analyzed within the framework of a simple model of a semiconductor with two types of carriers of one sign, indicate the existence of an impurity band. The values of the gap between the main and impurity band, the concentration of donors, and the concentration of the compensating acceptors are calculated. The mobility above 100 K is described by scattering of conduction band electrons at phonons and impurities. The sharp drop at low temperatures is explained by a crossover to Mott-type variable-range hopping in the impurity band.

Native Defect Nature of Electrical Centres in Low-Resistivity Zinc Selenide

Hall effect, electric conductivity and electron mobility in n-ZnSe crystals, annealed in Zn melt at temperatures from 500 to 950 °C, are studied in the temperature range from 55 to 500 K. The sharp increase of the shallow donor concentration is accompanied by a decrease of their compensation from K = NA/ND = 0.91 to 0.35, and of the activation energy ED from 28 to 9 meV, as the annealing temperature of n-ZnSe crystals increases above 650 °C. At low annealing temperatures, the conductivity of n-ZnSe is determined by shallow non-controlling donors such as AlZn, GaZn, InZn. The concentration of VZn native defects compensating the shallow donors is sharply decreased and the concentration of the VSe shallow donors determining the conductivity of crystal is sharply increased, as the annealing temperature increases above 800 °C. The decrease of annealing temperature of the samples below 650 °C results in a drastic decrease of the conductivity of the crystal, a decrease of electron concentration, and abnormally low mobility values. The observed anomalies of transport effects are found to be caused by the presence of a random potential relief in n-ZnSe samples.

Hall effect of the colossal magnetoresistance manganiteLa1−xCaxMnO3

The Hall resistivity ${\ensuremath{\rho}}_{H}$ and magnetoresistance of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ ${(T}_{c}=265$ K) have been measured at temperatures to 360 K in fields $H$ to 14 T. By comparing ${\ensuremath{\rho}}_{H}$ with the magnetization $M$, we have extracted the anomalous coefficient ${R}_{s}.$ We uncover an interesting relationship: ${R}_{s}$ is proportional to the zero-field resistivity from 200 to 360 K. Above ${T}_{c},$ the Hall angle $\mathrm{tan}{\ensuremath{\theta}}_{H}\ensuremath{\sim}M$. Further, the effective Hall mobility is $H$ independent over a wide range of $H$. We contrast these scaling relations with the Hall effect in typical ferromagnets.

Germanium Thin Film Formation by Low‐Pressure Chemical Vapor Deposition

Thin films of polycrystalline germanium were formed by the pyrolysis of germane gas in a low‐pressure reactor. Process parameters investigated were deposition temperature in the range 250 to 350°C and pressure in the range 300 to 600 mTorr. The properties of the film have been characterized using transmission electron microscopy and x‐ray diffraction for structural analysis, atomic force microscopy for surface morphology analysis, secondary ion mass spectroscopy for compositional analysis, and Hall effect measurement for electrical parameter extraction, etc. High Hall effect mobility on the order of 300 cm2/V s was obtained, even at a relatively low deposition temperature of 300°. This makes the germanium thin films potentially very promising for low‐temperature device processing.

Low-temperature annealing of polycrystalline Si/sub 1-x/Ge/sub x/ after dopant implantation

Hall effect measurement was employed to study the isothermal annealing of boron or phosphorus implanted polycrystalline Si/sub 1-x/Ge/sub x/ thin films, with x varying from 0.3-0.55. X-ray diffraction and cross-sectional transmission electron microscopy were used to study the crystal structure, whereas X-ray photoelectron spectroscopy was used to determine the film composition and the chemical bonding states of the elements. In low-temperature (/spl les/600/spl deg/C) annealing, the conductivity, the dopant activation, and the Hall effect mobility decreased during extended annealing. The effective activation of phosphorus was less than 20% and decreased with increasing Ge content. Boron activation could reach above 70%. It was also found that Si/sub 1-x/Ge/sub x/ could be oxidized at 600/spl deg/C in a conventional furnace even with N/sub 2/ protection, especially for phosphorus doped films with high Ge content. Consequently, a low-temperature SiO/sub 2/ capping layer is necessary during extended annealing.

The influence of CH4/H2/Ar plasma etching on the conductivity of n-type gallium nitride

The influence of plasma etching on the electrical properties of n-type gallium nitride (GaN) thin films has been investigated. Electron-cyclotron-resonance microwave plasma reactive ion etching in CH4/H2/Ar, in CH4/H2, and in H2 results in an increase in the GaN layer’s sheet carrier concentration and a decrease in the effective Hall mobility. Neither wet chemical etching nor etching in Cl2 or BCl3 plasmas introduces similar changes. Therefore, the observed damage is considered to be related to the CH4/H2/Ar plasma chemistry. In particular, it suggests hydrogen influence on the defect generation. Subsequent annealing of the affected GaN layers at 800 °C removes the plasma damage.

Improvement of implanted layer properties of semi-insulating GaAs by ingot annealing

The electrical properties and structural quality of wafers from lightly Cr-doped semi-insulating (SI) GaAs crystal before and after the three-step ingot annealing (IA) were studied. Comparison is based on the characteristics of seed and tail slices of the as-grown ingot and slices from seed and tail annealed slices cut normal to the growth axis. The carrier concentration profiles of implanted active layers were determined by C– V measurement with double mercury probe. Values of equivalent sheet carrier concentration, average low-field sheet Hall-effect mobility, and activation efficiency were obtained by measurement of the sheet Hall coefficient and the sheet resistivities of the square Hall-effect pattern. Spatially resolved cathodoluminescence (CL) of the investigated wafers is presented to support the interpretation of observed results.

Hall Effect and Resistivity Characterization of Doped, Electrodeposited CdSe

Doped thin films were electrodeposited onto indium‐tin oxide (ITO) substrates that were pretreated with a thin layer of Se, Cd, or In. Hall effect and resistivity measurements were performed to determine the effects of doping on the resistivity, carrier concentration, and carrier mobility. The data varied in a systematic fashion that correlated with the substrate treatment and doping procedures. Carrier concentrations ranged from 1019 to 109 cm−3, and the electrical resistivities were measured in the range of . Hall effect mobilities were in the range of 1–50 cm2/Vs. As doping levels increased, both resistivity and mobility decreased. Samples deposited on vapor treated ITO showed consistently high resistivities and moderate mobility values. When electrochemical treatments of ITO were used, the properties varied systematically with the amount of Cd or In electrodeposited, exhibiting resistivities in the lower range and carrier densities in the higher range. The temperature dependent resistivity and Hall effect data were analyzed using the Seto‐Baccarani model for polycrystalline semiconductors. This model assumes that the dominant transport mechanism is thermionic emission of carriers over the potential barriers that form at the intercrystalline grain boundaries.

ELECTRICAL TRANSPORT MEASUREMENTS IN LOW MOBILITY TWO-DIMENSIONAL ELECTRON GASES: EFFECT OF THERMOELECTRIC POWER

Quantum Hall Effect (QHE) and field effect mobility (in zero magnetic field) were measured in commercial low mobility n-channel MOSFETs. All the samples, at least in the region of higher mobility, show the quantized values of the Hall resistance. However we have identified a strong effect of the "aging" of the samples: a "new" sample shows the usual QHE curves and smooth field effect mobility curves, while an "aged" sample shows pronounced peaked structures superimposed on the normal field effect mobility. The QHE curves also show an anomalous behaviour superimposed on the usual one, We attribute the deformation of the QHE curves to an onset of a thermoelectromotive force related to electric fields which produce non-uniform electron energy distribution along the channel. We give evidence of thermoelectric effects by measurements on a high quality Hall geometry MOSFET. Our experiments indicated an approximately linear dependence of the thermoelectric voltage on the electric field along the sample.

Structural and Electrical Properties of Heteroepitaxial HgCdTe/CdZnTe/GaAs/Si

ABSTRACTThe structural and electrical properties of heteroepitaxial HgCdTe/CdZnTe/GaAs/Si were evaluated using high-resolution x-ray diffraction techniques and Hall-effect measurements as a function of temperature. Significant tilting of the layers was found for both {100} and {111} CdZnTe layers grown on misoriented {100}GaAs/Si substrates, consistent with the interpretation of a low-angle tilt boundary being formed at the interface to relieve the large lattice mismatch between the layers. The GaAs layer is in a state of biaxial tension before and after the growth of the CdZnTe layers. The x-ray FWHM of HgCdTe layers grown by LPE on these substrates was found to be reduced from that of the MOCVD-grown CdZnTe buffer layer due to both an annealing effect during LPE growth and to the increased distance of layer surface from the defective CdZnTe/GaAs interface. Hall-effect mobility for {100}HgCdTe layers was nearly identical to that of layers grown on bulk CdZnTe substrates. High-quality heterojunction infrared detectors have been fabricated using these materials.

Hall coefficient and oxygen stoichiometry in YBa2Cu3O7- delta ceramics at elevated temperatures.

The Hall coefficient and resistivity of polycrystalline ceramic samples of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ were measured at elevated temperatures and at various ambient O/sub 2/ partial pressures and correlated with separate thermogravimetric measurements of delta. In the region where the oxygen stoichiometry reaches equilibrium with the external O/sub 2/, it is shown by isothermal plots that the Hall number density decays exponentially with increasing delta and the effective Hall mobility is weakly dependent on delta. Although transport coefficients are temperature dependent, this result lends support to the picture that oxygen doping in the cuprate acts mainly to modulate the density of hole carriers.

Hall effect of the high T c superconducting Y-Ba-Cu-O compound

The Hall coefficient R h of Y-Ba-Cu Oxide has been measured from room temperature to ∼ 90K. R h is positive and temperature dependent down to ∼ 125K below which it becomes less temperature dependent. No anomaly of the effective Hall mobility occurs around 125K and the resistivity is independent of magnetic field in the whole temperature range. The onset of superconductivity near 125K in this compound has not been confirmed by the present measurements.

In-situ mobility profiling of GaAs MESFET's using the hall current technique

A novel experimental technique to perform in-situ Hall effect mobility profiling of short-channel devices is described in this paper. This is based on the measurement of the Hall current in the conduction channel of a transistor with a split source or drain contact. The mobility is then determined by a simple expression relating the Hall current, the physical dimensions of the channel, the total current injected in the device, and the magnetic induction. No special structure is required and the measurements can be performed on the usual MESFET or MODFET geometries. The same technique can also be used with devices fabricated on lower mobility materials such as silicon where the geometrical magnetoresistance measurements are not practical. Using the new technique, we have obtained spatial Hall mobility profiles in commercially available GaAs MESFET's. Our experimental results are in good agreement with data obtained by other researchers using magnetoresistance measurements. Finally, some theoretical and practical problems associated with our technique are discussed.

Growth and properties of AlGaAs/GaAs heterostructures on GaAs (110) surface

We report on MBE growth of high quality modulation doped heterostructures on GaAs (110) without intentional misorientation. PL measurements have shown that a high quality (110) 2DEG system was obtained. Quantum Hall effect measurements and mobility enhancement results show that the AlGaAs/GaAs(110) interface displays the same two-dimensional electron gas characteristics as the AlGaAs/GaAs (100) interface.

Hydrogen Neutralization of Shallow-Donor Impurities in Single-Crystal Silicon

ABSTRACTNew data are presented that considerably strengthen the conclusion, reported previously, that hydrogen can passivate shallow donors in silicon by associating with them to form neutral complexes. Effects of inhomogeneity of doping with depth have been eliminated in the new experiments; the observed increase of the effective Hall mobility after hydrogenation requires neutralization of ionizeddonor scattering centers.

ELECTRICAL TRANSPORT PROPERTIES OF IODINE DOPED POLYACETYLENE

Measurements of the DC conductivity and the 10 GHz microwave conductivity of iodine doped cis and trans polyacetylene in the temperature range from 4.2 K to 300 K are reported. At room temperature no sample shows a frequency dependence ; at low temperatures, however, the microwave conductivity of moderately doped samples is considerably higher than the DC value. From the magnetoresistance at liquid helium temperature an effective Hall mobility in the order of magnitude of 102cm2/Vsec is estimated for samples with various iodine concentrations.

Electron mobility enhancement in epitaxial multilayer Si-Si1−xGex alloy films on (100) Si

Enhanced Hall-effect mobilities have been measured in epitaxial (100)-oriented multilayer n-type Si/Si1−xGex films grown on single-crystal Si substrates by chemical vapor deposition. Mobilities from ∼20 to 40% higher than that of epitaxial Si layers and ∼100% higher than that of epitaxial SiGe layers on Si were measured for the doping range ∼8×1015–∼1017 cm−3. The mobilities of multilayer Si/SiGe films approach that of single-crystal Si films at ∼2×1017 cm−3. No mobility enhancement was observed in multilayer p-type (100) films and n-type (111)-oriented films. Experimental studies included the effects upon film properties of layer composition, total film thickness, doping concentrations, layer thicknesses, and growth temperature.

Transport properties of a-Si: H alloys prepared by r.f. sputtering

Abstract Conductivity and thermopower measurements as a function of temperature are reported for a series of r.f. sputtered hydrogenated a-Si samples doped with P. The results are analysed, along with others in the literature, in terms of several models for transport. It is concluded that the best overall fit to the data involves conduction in an intrinsic band above about 400 K and conduction in a P-related impurity band between about 200–400 K. The proposed transport in the latter temperature regime disagrees with earlier conclusions of Spear and Le Comber, and it also implies a smaller shift of the Fermi level with doping than does their model. The implications of this interpretation for current measurement of Hall effect and drift mobility are briefly outlined, as are difficulties in the detailed interpretation and complications related to heterogeneity in structure.

Transport properties of a-Si: H alloys prepared by r.f. sputtering I

Abstract Conductivity and thermopower measurements as a function of temperature are reported for a series of r.f. sputtered hydrogenated a-Si samples doped with P. The results are analysed, along with others in the literature, in terms of several models for transport. It is concluded that the best overall fit to the data involves conduction in an intrinsic band above about 400 K and conduction in a P-related impurity band between about 200–400 K. The proposed transport in the latter temperature regime disagrees with earlier conclusions of Spear and Le Comber, and it also implies a smaller shift of the Fermi level with doping than does their model. The implications of this interpretation for current measurement of Hall effect and drift mobility are briefly outlined, as are difficulties in the detailed interpretation and complications related to heterogeneity in structure.