Average Drift Mobility Research Articles

Phonon Mediated Electron-Electron Scattering in Metals

It is shown that the linear resistivity dependence on temperature for metals above the Debye’s temperature mainly is caused by electron-electron scattering of randomly moving electrons. The electron mean free path in metals at this temperature range is in inverse proportion to the effective density of randomly moving electrons, i.e. it is in inverse proportion both to the temperature, and to the density-of-states at the Fermi surface. The general relationships for estimation of the average diffusion coefficient, the average velocity, mean free length and average relaxation time of randomly moving electrons at the Fermi surface at temperatures above the Debye’s temperature are presented. The effective electron scattering cross-sections for different metals also are estimated. The calculation results of resistivity dependence on temperature in the range of temperature from 1 K to 900 K for Au, Cu, Mo, and Al also are presented and compared with the experimental data. Additionally in temperature range from 1 K to 900 K for copper, the temperature dependences of the mean free path, average diffusion coefficient, average drift mobility, average Hall mobility, average relaxation time of randomly moving electrons, and their resultant phonon mediated scattering cross-section are presented.

Formation of secondary electron cascades in single-crystalline plasma-deposited diamond upon exposure to femtosecond x-ray pulses

Secondary electron cascades were measured in high purity single-crystalline chemical vapor deposition (CVD) diamond, following exposure to ultrashort hard x-ray pulses (140fs full width at half maximum, 8.9keV energy) from the Sub-Picosecond Pulse Source at the Stanford Linear Accelerator Center. We report measurements of the pair creation energy and of drift mobility of carriers in two CVD diamond crystals. This was done for the first time using femtosecond x-ray excitation. Values for the average pair creation energy were found to be 12.17±0.57 and 11.81±0.59eV for the two crystals, respectively. These values are in good agreement with recent theoretical predictions. The average drift mobility of carriers, obtained by the best fit to device simulations, was μh=2750cm2∕Vs for holes and was μe=2760cm2∕Vs for electrons. These mobility values represent lower bounds for charge mobilities due to possible polarization of the samples. The results demonstrate outstanding electric properties and the enormous potential of diamond in ultrafast x-ray detectors.

Drift mobility and the frequency response of diode connected organic transistors

A method to characterize the frequency response of an organic field effect transistor (FET) is presented. Analysis then shows a method to calculate the average drift mobility from the frequency at which a pole appears in the response. This pole is believed to appear at the point where charge carriers can no longer fully traverse the channel in one period of the input signal. The dc output characteristics of the device are also described, and saturation mobility values are derived. This saturation mobility and the drift mobility calculated from the frequency response are comparable. This method can be used in determining the drift mobility in other materials such as single nanowires in the FET configuration.

Carrier transport properties in high resistivity polycrystalline CdZnTe material

Abstract The electrical properties of polycrystalline CdZnTe (Zn = 4%) having high resistivity (3.3 × 10 9 Ω cm) were investigated by using the time-of-flight technique. We have found that the average drift mobility of as-deposited polycrystalline CdZnTe samples is 1.21 cm 2 /V s and the electron trapping time is 4.6 μs. In a comparison of annealed samples at different conditions, the variation of resistivity in polycrystalline CdZnTe is considered to be mainly related to the fluctuation of carrier concentration, which originates from the change of density in deep level.

Characterization of high-resistivity poly-CdZnTe thick films grown by thermal evaporation method

The high-resistivity polycrystalline CdZnTe thick films are grown by thermal evaporation method. The electrical properties of polycrystalline CdZnTe having high resistivity were investigated using time of flight technique. We have measured the average drift mobility and mobility lifetime of polycrystalline CdZnTe. In the comparison of annealed samples at different conditions, the variation of resistivity in the polycrystalline CdZnTe is considered to be related to the fluctuation of carrier concentration. From the analysis of transient photocurrent of time of flight based on multiple trapping model, we have found that the two dominant localized states which is considered to be related to the Cd vacancy (E/sub V/+0.36 eV), and grain boundary defects (E/sub V/+0.75 eV) play a dominant role in increasing resistivity through compensation process.

Average Drift Mobility and Apparent Sheet-Electron Density Profiles in Strained-Si–SiGe Buried-Channel Depletion-Mode n-MOSFETs

In this paper, we describe a simple method to extract the average drift mobility and the apparent sheet electron density versus the applied gate voltage and the vertical effective electric field in strained-Si-SiGe buried-channel depletion-mode metal-oxide semiconductor field-effect transistors (n-MOSFETs). For this, we adapted an established technique used in evaluating mobility profiles in Schottky-gate MESFETs, by taking into account the existence in our devices of the gate-oxide capacitance C/sub ox/ and by introducing an effective junction capacitance C/sub D/, which follows the ideal Schottky's depletion approximation. By applying our method on fabricated transistors we were able to obtain the average drift mobility profile versus the applied vertical effective field and monitor values as high as 618 cm/sup 2//Vs. We also extracted the apparent sheet electron density profile with values reaching as high as 3.4 /spl times/ 10/sup 12/ cm/sup -2/. Although the layer design had not been optimized, the results show mobility enhancement in the strained silicon channel and, to our view, point to a unique regime of operation for these devices, which should benefit the low-power and low-voltage applications. The proposed method could be used as a nondestructive tool for monitoring the transport properties in Si-SiGe modulation-doped MOSFETs. It could also serve as a useful platform for determining explicit modeling links between the layer design and the device performance.

High-frequency electron conductivity mobility in vapor-phase homoepitaxial silicon

The average room-temperature electron conductivity mobility μc in silicon measured at ultrahigh frequencies was found to be approximately 30% higher than the average drift mobility reported in the literature for bulk samples with identical resistivity. The discrepancy is attributed to the minimized effect of traps in silicon at ultrahigh frequencies where the period of the rf signal is considerably shorter than the lifetime of the traps.

Measurement of Seebeck and Hall effects in compactions of TCNQ salts

Electrical conductivity, activation energy for conduction, thermoelectric power and Hall mobility have been measured in compactions of a series of simple and complex TCNQ salts. The results indicate nearly intrinsic semi-conduction in extremely narrow bands, with an average drift mobility of about 10–2 cm2/Vs.