Temperature dependence of polaron cyclotron resonance mass in GaAs/AlGaAs heterostructures

The temperature dependence of polaron cyclotron resonance mass in GaAs/AlGaAs heterostructures is reinvestigated theoretically. By taking into account the electron-longitudinal-optic phonon interaction with temperature-dependent many-body effects, the conduction band non-parabolicity, and the influence of nonzero magnetic field, a good agreement with experiment is obtained.

Blocking of the polaron effect and spin-split cyclotron resonance in a two-dimensional electron gas

Cyclotron resonance (CR) of high density GaAs quantum wells exhibits well-resolved spin splitting above the LO-phonon frequency. The spin-up and spin-down CR frequencies are reversed relative to the order expected from simple band nonparabolicity. We demonstrate that this is a consequence of the blocking of the polaron interaction which is a sensitive function of the filling of the Landau levels.

Cyclotron resonance mass of magnetopolaron in a polar crystal slab at finite temperatures

Using the Green function method, we have studied the cyclotron resonance of an electron interacting with bulk longitudinal optical(BO) phonons as well as surface optical(SO) phonons in a polar crystal slab at finite temperatures. It is found that the temperature dependence of magnetopolaron depends strongly on the strength of the magnetic field. The numerical results show that the cyclotron resonance mass of polaron in a slab is an increasing or decreasing function of temperature when the magnetic field is lower or higher than the resonant magnetic field region, respectively. The magnetic field and slab width dependence of cyclotron resonance mass are also studied in this paper. (C) 1999 Elsevier Science B.V. All rights reserved.

High-field cyclotron resonance and electron-phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B > similar to 23 T), the three samples behave very differently. For the most lightly doped sample (3 x 10(11) cm(-2)) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6 x 10(11) cm(-2)) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2 x 10(12) cm(-2)) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR. (C) 1998 Elsevier Science B.V. All rights reserved.

Cyclotron-resonance mass of two-dimensional electrons in GaN/AlxGa1-xN heterostructures

The electron cyclotron-resonance (CR) mass of quasi-two-dimensional electrons in GaN/AlxGa1-xN heterostructures is studied theoretically. The correction to the CR mass due to electron-phonon interaction is investigated, taking into account band nonparabolicity, the occupation effect, and the screening of the electron-phonon coupling. The dependence of the CR mass on the electron density and on the magnetic field strength is displayed in detail, and the calculated CR mass agrees well with a recent experiment. We found that the effective electron-phonon coupling strength in GaN heterostructures is reduced below the bulk value.

High-field cyclotron resonance and electron-phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B > similar to 23 T), the three samples behave very differently. For the most lightly doped sample (3 x 10(11) cm(-2)) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6 x 10(11) cm(-2)) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2 x 10(12) cm(-2)) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR. (C) 1998 Elsevier Science B.V. All rights reserved.

Investigation on bioactivity of titanium dioxide thin films fabricated by electron cyclotron resonance plasma aided pulsed laser deposition

Titanium dioxide thin films with a rutile crystallinite size around 20 nm were fabricated by pulsed laser deposition (PLD) aided with an electron cyclotron resonance (ECR) plasma. With annealing treatment, the crystal size of the rutile crystallinite increased to 100 nm. The apatite-forming ability of the films as deposited and after annealing was investigated in a kind of simulated body fluid with ion concentrations nearly equal to those of human blood plasma. The results indicate that ECR aided PLD is an effective way both to fabricate bioactive titanium dioxide thin films and to optimize the bioactivity of titanium dioxide, with both crystal size and defects of the film taken into account.

Electron Cyclotron Resonance in Strained Si and Si0.94Ge0.06 Channels on Relaxed Si0.62Ge0.38 Buffers Grown by Rapid Thermal Chemical Vapor Deposition

We report the far-infrared measurements of the electron cyclotron resonance absorption in n-type Si/Si0. 62Ge0.38 and Si0.94Ge0.06 /Si0. 62Ge0.38 modulation- doped heterostructures grown by rapid thermal chemical vapor deposition. The strained Si and Si0.94Ge0.06 channels were grown on relaxed Si0.62Ge0.38 buffer layers, which consist of 0.6 μm uniform Si0.62Ge0.38 layers and 0.5 μm compositionally graded relaxed SiGe layers from 0% Ge to 38 % Ge. The buffer layers were annealed at 800 °C for 1 hr to obtain complete relaxation. The samples had 100 Å spacers and 300 Å 2×1019 cm-3 n-type supply layers on the tops of the 75 Å channels. The far-infrared measurements of electron cyclotron resonance were performed at 4K with the magnetic field of 4 – 8 Tesla. The effective masses determined from the slope of center frequency of absorption peak vs applied magnetic field plot are 0.20 mo and 0.19 mo for the two dimensional electron gases in the Si and Si0.94Ge0.06 channels, respectively. The Si effective mass is very close to that of two dimensional electron gas in Si MOSFET (0.198mo). The electron effective mass of Si0.94Ge0.06 is reported for the first time and about 5 % lower than that of pure Si.

Synthesis of free standing carbon nanosheet using electron cyclotron resonance plasma enhanced chemical vapor deposition

Carbon nanosheets (CNSs) have been synthesized by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) using a mixture of acetylene and argon gases on copper foil as the substrate. Micrometer-wide carbon sheets consisting of several atomic layers thick graphene sheets have been synthesized by controlled decomposition of carbon radicals in ECR-PECVD. Raman spectroscopy of these films revealed characteristics of a disordered graphitic sheet. Thick folded carbon-sheets and a semi transparent freestanding CNSs have been observed by scanning electron microscopy. This is a promising technique to synthesize free standing CNSs and can be used in the fabrication of nanoelecronic devices in future. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis of 3-dimensional porous graphene nanosheets using electron cyclotron resonance plasma enhanced chemical vapour deposition

Microwave plasma driven chemical vapour deposition was used to synthesize graphene nanosheets from a mixture of acetylene and hydrogen gas molecules. In this plasma, acetylene decomposes to carbon atoms that form nanostructures in the outlet plasma stream and get deposited on the substrate. The GNS consists of a few layers of graphene aligned vertically to the substrate. Graphene layers have been confirmed by high-resolution transmission electron microscopy, and Raman spectral studies were conducted to observe the defective nature of the sample. The growth of nanosheets in a vertical direction is assumed to be due to the effect of electric field and from the difference in the deposition rate in the axial and parallel directions. These vertical graphene sheets are attractive for various applications in energy storage and sensors.

Two-dimensional simulation of an electron cyclotron resonance plasma source with self-consistent power deposition

Using a refined two-dimensional hybrid-model with self-consistent microwave absorption, we have investigated the change of plasma parameters such as plasma density and ionization rate with the operating conditions. The dependence of the ion current density and ion energy and angle distribution function at the substrate surface vs. the radial position, pressure and microwave power were discussed. Results of our simulation can be compared qualitatively with many experimental measurements.

Effect of hydrogen dilution on the deposition of carbon-rich a-SiC:H films by the electron cyclotron resonance method

The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) process is reported. The variation in the deposition and film characteristics such as the deposition rate, optical band gap and IR absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of about 250 Å min-1 at a hydrogen dilution ratio of about 20 (hydrogen flow (sccm)/acetylene + silane flow (sccm)) and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical band gap on the hydrogen dilution within the dilution range investigated (10-60) and the optical band gap calculated from the E04 method varied marginally from about 2.85 to 3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of about 2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of about 30. The PL intensity showed a strong dependence on the hydrogen dilution variation.

Study on the ions' behavior in an electron cyclotron resonance plasma

The energy, velocity, angle distribution of ions in magnetoactive electron cyclotron resonance plasma have been studied with a two-dimension hybrid mode. The dependence of these distribution functions versus position and pressure are discussed. Our simulation results are in good agreement with many experimental measurements. (C) 1997 American Institute of Physics.

The effects of coil current distribution in a cylindrical electron-cyclotron-resonance reactor

Using a 2-D hybrid model, the authors have found that external currents play an important role in the plasma parameters in the reactor. The plasma density, temperature and electrostatic potential would be significantly influenced by the applied external currents.