Carrier Mobility Ratio Research Articles

Voltage Transfer Characteristics of CMOS-Like Inverters for Ambipolar SnO Thin-Film Transistors

The voltage transfer characteristics (VTC) of complementary metal-oxide-semiconductor (CMOS)-like inverter using ambipolar SnO-thin-film transistor were analyzed based on analytical simulation to extract ambipolar parameters such as majority/minority carrier mobility. The unbalanced majority carrier mobilities caused by the inferior electron mobility limited the inverter characteristics, and the minority carrier conduction resulted in non-full swing Z-shape VTC in the oxide-CMOS-like inverter. We found that a majority/minority carrier mobility ratio was a key parameter to improve the VTC by reducing the subgap defect states in SnO channel. We also fabricated 3-stage ring oscillator using the CMOS-like inverters and confirmed the ambipolar operation with positive/negative supply voltages.

A comprehensive study on carrier mobility and artificial photosynthetic properties in group VI B transition metal dichalcogenide monolayers

Artificial photosynthesis in group VI B transition metal dichalcogenide monolayers.

Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy

The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit (ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77–300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.

Conductivity-limiting bipolar thermal conductivity in semiconductors.

Intriguing experimental results raised the question about the fundamental mechanisms governing the electron-hole coupling induced bipolar thermal conduction in semiconductors. Our combined theoretical analysis and experimental measurements show that in semiconductors bipolar thermal transport is in general a “conductivity-limiting” phenomenon, and it is thus controlled by the carrier mobility ratio and by the minority carrier partial electrical conductivity for the intrinsic and extrinsic cases, respectively. Our numerical method quantifies the role of electronic band structure and carrier scattering mechanisms. We have successfully demonstrated bipolar thermal conductivity reduction in doped semiconductors via electronic band structure modulation and/or preferential minority carrier scatterings. We expect this study to be beneficial to the current interests in optimizing thermoelectric properties of narrow gap semiconductors.

Use of lateral structures to monitor and evaluate degradation of key photovoltaic parameters in an organic bulk heterojunction material

Charge transport and recombination mechanisms within organic bulk heterojunction (BHJ) systems have been studied using lateral devices to perform in situ potentiometry. We have developed a simplified measurement technique using two types of lateral structures to elicit key charge transport parameters and study the time and process dependence of the carrier mobilities and their ratio. Small geometry lateral devices are used to evaluate the mobility of the slower carrier within the P3HT:PCBM material system. Larger structures with 5 in situ voltage probes are used to construct a simple potential profile of the device channel and accurately determine the carrier mobility ratio. These two measurements enable the calculation of carrier densities and the recombination coefficient. We monitor the change in these parameters as the P3HT:PCBM film degrades in the presence of oxygen and also examine the effect of the solvent additive 1,8-diiodooctane on this degradation mechanism. By exposing ethanol vapor to the BHJ film, we induce traps in the material and monitor the shift in dominant nongeminate recombination mechanism to a more unimolecular type. We are also able to measure the resulting decrease in carrier mobilities due to the presence of dipole-induced traps. Lateral devices are useful material diagnostic structures for studying degradation in BHJ materials.

Investigation of the acceptor and donor in fast neutron irradiated Czochralski s ilicon

Variations of the irradiated defects, resistivity, carrier mobility ratio and ca rrier concentration in high-dose neutron-irradiated n-type Czochralski silico n have been investigated by means of Fourier transform infrared spectrometer, po sitron annihilation spectroscopy and Hall effect. After irradiated with fast neu tron, the sample transformed from n to p-type. Two types of acceptor centers th at contribute to the V22O22, V22O, VO22, V-O-V and V 44-type defects will appear after annealing at temperature of 450 a nd 600 ℃, respectively. After annealing at temperatures above 650℃, with the elimin ation of acceptors, the carrier mobility ratio and the carrier-type began to re cover and a type of donor related to the irradiated defects will appear. The eff ective annealing temperature is 750℃ at which the donor is formed, and anneal ing above 900℃ for 1h will eliminate the donor.

Current gain in photodiode structures

We show that the electric field which is responsible for the removal of excess majority carriers created when a photodiode is illuminated induces an additional minority carrier current flow to the diode junction. This effect is particularly marked when the bulk semiconductor has mixed conductivity and when the minority to majority carrier mobility ratio is high, and can be the cause of anomalously low junction resistance in photodiodes.

Current Carrier Mobility Ratio in Semiconductors

Current Carrier Mobility Ratio in Semiconductors