Two different modes of electron heating are found in microwave discharges: the bulk heating mode characterized with low electron density n e and high electron temperature T e (∼10 eV), and the surface heating mode with high n e and low T e (∼3 eV). The correlation between the heating mode and the electron energy distribution function (EEDF) is qualitatively interpreted in terms of non-local kinetic theory, taking account of the ambipolar potential well. A biased optical probe diagnostics of a surface wave plasma (SWP) reveals that the surface heating mode gives a bi-Maxwellian type EEDF, that is, a sum of two Maxwellian distributions of bulk temperature T b and tail temperature T t > T b . On the other hand, the EEDF of inductively coupled plasma (ICP) is close to a single-Maxwellian distribution with electron temperature higher than the bulk temperature T b of the SWP. Such differences in the EEDFs make the composition of the reactive species of the two plasmas different; namely, ion and radical measurements at the same electron density show that the ICP contains more F radicals and less CF 3 and CF 2 radicals in comparison with the SWP. In addition, a simplified model based on the bi-Maxwellian EEDF shows how the EEDF determines the ion and radical compositions, supporting the major experimental results. These observations and calculations suggest that plasma chemistry is controllable by tailoring the EEDF with proper adjustment of bulk heating and/or surface heating of electrons.

Large-diameter high-density plasmas such as electron-cyclotron-resonance (ECR), helicon wave, inductively coupled, and surface-wave plasmas are currently being developed for plasma-assisted thin-film processes in the next generation. Actual applications of such high-density plasmas require a deeper understanding of discharge physics as well as advanced techniques for plasma control. In this paper, new findings on antenna-plasma couplings are reported. One is resonant directional excitation of helicon waves and a mechanism of density jump in a helicon RF discharge. The other is the identification of long-wavelength surfacewave modes with observation of the short-wavelength mode in a planar microwave discharge. In addition, comprehensive diagnostics of a pulsed inductively coupled plasma in chlorine is presented, which explains the pronounced effect of pulsed power discharges on charge-up suppression.

The optical constants and bandgap energy (E g) of semiconductors, characterized by spectroscopic ellipsometry (SE), are highly affected by the applied model dielectric function (MDF). In this study, we investigated the optical constants and E g in low indium content (x) Al1-x In x N alloys grown on a c-plane freestanding GaN substrate by using SE, and their applied MDF dependence was investigated. The tanΨ and cosΔ spectra, in a photon energy range of 1.5–5.0 eV, of high-quality crystalline Al1-x In x N alloys were well fitted by Adachi’s critical-point (ACP) model. The ACP model exhibited better spectral fitting results than did the Tauc–Lorentz model, which has often been adopted for Al1-x In x N alloys. The accuracy of the E g values obtained by the ACP model was confirmed by optical reflectance measurements. It is suggested that the ACP model is a suitable MDF for recent high-quality crystalline Al1-x In x N alloys as well as other III-nitride semiconductors.

The effects of the plasma profile on the global energy confinement have been studied in Heliotron E with special regard to differences between heating methods (ECH, NBI and NBI + ECH). With high power NBI, peaked Ti and peaked ne profiles (Ti(0)/⟨Ti ⟩ ≲ 2.7, ne(0)/⟨ne⟩ ≲ 4.5) were simultaneously achieved under low recycling conditions. A peaked ne profile (ne(0)/⟨ne⟩ ≳ 2.5 ) could lead to the high Ti mode where the ion heat transport in the central region is substantially reduced. By changing the ECH launching condition (on-axis, off-axis and toroidally oblique injection), the peakedness of the Te profile could be controlled in the range 1.3 ≲ Te(0)/⟨Te⟩ ≲ 4.5. A peaked Te profile and a flat ne profile (3.5 ≲ Te(0)/⟨Te⟩, ne(0)/⟨ne⟩ ≲ 1.8) were brought about by the well focused on-axis ECH. The ECH plasma with a peaked Te profile has higher stored energy than that with a moderately peaked Te profile for the same injected ECH power and the same density region. The global energy confinement time normalized by the LHD scaling, τE G/τE LHD, showed ne(0)/⟨ne⟩ dependence for the low Ti mode NBI plasmas. For the high Ti mode, the ne(0)/⟨ne⟩ dependence of τE G/τE LHD was weak. These findings suggest that the LHD scaling should be modified to scale the global energy confinement of the helical plasmas in a wide range of ne(0)/⟨ne⟩.

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