The surface phonon dispersion was investigated by high-resolution electron-energy-loss spectroscopy on the deuterium-terminated Si͑111͒-͑1 ϫ 1͒ prepared by an improved wet chemical method. The phonon modes were recorded over the entire surface Brillouin zone and compared with the theoretical phonon dispersion curves derived on the basis of semiempirical total-energy scheme calculated by Sandfort et al. ͓Phys. Rev. B 51, 7139 ͑1995͔͒ and by Gräschus et al. ͓Surf. Sci. 368, 179 ͑1996͔͒. The present results of the observation fairly agree with the theoretical curves, except a discrepancy for B 3 and R 1 branches exhibiting a sizable dispersion between 35 and 55 meV, which was predicted to have no dispersion by the theory. The suface-projected bulk phonon is distributed below 65 meV of the vibration energy, and the Si-D modes with higher energies than that are independent of SPBP. The Si-D vibrations with energies between 35 and 65 meV strongly intermix with bulk phonons, and below 35 meV, the Si-D's move together in phase and the surface phonons are the same as those of hydrogen-terminated Si͑111͒-͑1 ϫ 1͒.
In AlGaN/GaN high-electron-mobility transistors (HEMTs) with an AlN spacer layer, which improves two-dimensional electron gas (2DEG) properties, it is important to decrease ohmic contact resistance because an AlN spacer layer with an extremely wide band gap decreases the contact resistance significantly. We employed Si ion implantation doping to solve this problem and successfully obtained a sufficiently low contact resistance equivalent to that of HEMT without an AlN spacer layer. In the fabricated AlGaN/AlN/GaN HEMTs with Si-ion-implanted source/drain contacts, as another effect of AlN spacer layer insertion, a reduction in the forward Schottky gate current was found, which made it possible to apply a high gate voltage in the transistor operation. Combined with the improvement in 2DEG properties, a marked enhancement in drain current density of 25–30% was observed.
The gas composition is one of the most important parameters for reducing process temperature of the plasma enhanced chemical vapor deposition. We investigate the effect of the gas flow rate of SiH4, H2, and N2 on the quality and the deposition rate of the silicon nitride films (SiNx) formed by the microwave excited PECVD. The SiH4 flow rate is most important parameter for controlling the deposition rate and the film quality in the PECVD using N2, H2, SiH4 gasses. The deposition rate strongly depends on the SiH4 flow rate; however the film quality was degraded with the increase of the flow rate. The hydrogen has an optimum flow rate for the high deposition rate and high quality film formation. The hydrogen effectively dissociates the SiH4 gas and makes the nitridation species (NHx), as the result, the optimal hydrogen improves the reaction efficiency of SiH4 and NHx.
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