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A high-temperature oxygen annealing (HiTOA) process has been developed to recover the degradation of the electrical characteristics due to the nitrogen incorporation into the HfAlOx film. The HiTOA process was carried out after the introduction of the nitrogen atoms. This process affected the bonding configuration of the nitrogen atom coordinated to the hafnium atom, and reconverted the nitrogen atom into an oxygen one. Therefore, this substitution markedly recovered the gate leakage current through the HfAlOxN film with a slight increase in the equivalent oxide thickness. Additionally, it significantly improved the effective mobility of n+ polycrystalline silicon (poly-Si) gate n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs).

Fully silicided platinum gates have been proposed as metal gate electrodes for scaled complementary metal oxide semiconductor field-effect transistors (CMOSFETs). The Pt monosilicide (PtSi) phase was formed on gate dielectrics by a full silicidation reaction at 400°C. PtSi gate electrodes on SiO2 possess a high effective work function of 4.9 eV, which could be used as a possible metal gate electrode for p-MOSFETs, while at the PtSi/HfO2 interface, Fermi-level pinning is observed independent of the PtSi fabrication process. The Fermi-level pinning at the PtSi/HfO2 interface is comparable to that at the poly-Si/HfO2 interface, and Fermi-level pinning does not occur at the Pt/HfO2 interface. These results show that Fermi-level pinning is induced by the presence of silicon atoms at the HfO2 upper interface.

In this study, we investigate effects of various buffer layers on the electrical properties of HfO2 metal–insulator–semiconductor (MIS) structures under fixed conditions for HfO2 deposition and postdeposition annealing. The buffer layers are prepared using several processes including oxidation, oxynitridation and nitridation. The equivalent oxide thickness (EOT), the flat-band voltage and the flat-band voltage hysteresis of the HfO2 MIS structures depend on the nitrogen density per unit area in oxynitride buffer layers. We reveal that the increase of EOT due to postdeposition annealing is suppressed by a certain amount of nitrogen density in oxynitride buffer layers. Based on the results, we propose an engineering methodology for the nitrogen composition and the physical thickness of the oxynitride buffer layers so as to obtain a high-performance MIS field-effect transistors.

We have studied photocurrent (PC) spectroscopic features of a relatively thick barrier GaAs/AlAs multiple quantum well p-i-n diode at 18 K. It is found that the PC spectra do not reflect the photoabsorption spectral lineshape under the low field condition and show negative PC peaks at the exciton resonance wavelengths where the absorption coefficient is maximum. These PC dips are qualitatively explained by considering the distribution of photogenerated carriers and competition between the carrier transport and recombination. A tunneling model calculation is carried out to successfully explain the PC spectral features as well as the field dependence of PC intensity by taking into account the photogenerated carrier distribution and the excitonic absorption lineshape variations with the field.

We have investigated the influence of Γ-X resonance on the photocurrent-voltage characteristics in GaAs/InAlAs type-I strained superlattices. To explain the experimental results, we have calculated the energies of the Γ and X electron states, which are confined in the GaAs and InAlAs layers, respectively, using an effective-mass approximation taking into account the strain effect. We conclude that the Γ1-X1 x y resonance causes peaky profiles in the photocurrent-voltage characteristics.

Strontium titanate ( SrTiO3) thin films were grown by means of the metalorganic chemical vapor deposition (MOCVD) method using dipivaloylmethane (DPM) chelate of strontium (II) [ Sr(DPM)2] and titanium tetraisopropoxide as source materials. In the preliminary experiments, the deposition behaviors of SrO and TiO2 films from respective sources were examined separately. As-grown perovskite single-phase SrTiO3 films were obtained at the substrate temperature of 750° C under the reduced pressure of 530 Pa. The films deposited on the MgO (100) substrate showed high (100) orientation and good optical transmission spectra, with the refractive index of 2.35. The dielectric constant and dielectric loss were 150–250 and 0.01–0.04, respectively. The leakage current density of the 0.38 µ m-thick films was approximately 3×10-8 A/cm2 at 3 V.

Tantalum pentaoxide thin films with orthorhombic structure have been grown on quartz and Si(100) substrates at 600∼700°C under reduced pressure of 5 Torr by metalorganic chemical vapor deposition. Ta(OC2H5)5 and Ta(DPM)4Cl were used as the source materials, and were compared with each other with respect to deposition behavior, crystal structure and orientation of Ta2O5 films. When the Ta(DPM)4Cl precursor was used, fine (111)-oriented Ta2O5 films were obtained on quartz and Si(100) substrates in a temperature range of 625∼675°C.

A high-power, 790 nm, eight-beam individually addressable AlGaAs laser array on 50 µm centers with a monitoring photodiode has been developed for high-speed data transfer in optical memory systems. The maximum output power of each element is over 80 mW. When eight elements are simultaneously operated at 20 mW in APC (Automatic Power Control) mode using the one-beam monitoring control, the total light output variation is less than 7% at a heatsink temperature between 10 and 50°C.

La-modified lead titanate (PLT) thin films are prepared by the metalorganic chemical vapor deposition method. Tetraethyl lead, titanium tetraisopropoxide and trisdipivaloylmethanato lanthanum are used as source materials. The films obtained at 600°C under reduced pressure of 6 Torr constitute PLT of the single perovskite phase, and highly c-axis-oriented films are grown on MgO(100). The crystal structures are transferred from the tetragonal to the cubic structure with increasing molar fraction of La2O3. The dielectric constant and tan δ are around 800 to 2700 and 0.04 to 0.1.

Ferroelectric PZT thin films were prepared by the simultaneous deposition of PbO, ZrO2 and TiO2 on heated substrates under a reduced pressure of 6 Torr. Both tetraethyl lead-zirconium tetraisopropoxide and tetradipivaloylmethane-titanium tetraisopropoxide systems were examined as source materials. The films obtained at 500° to 650°C with those systems were constituted of PZT of the single perovskite phase, and highly c-axis-oriented films were grown on MgO(100) with the latter system. The c-axis orientation suggests an epitaxial growth of PZT on the substrates. With increasing molar fraction of ZrO2 in the PZT, the crystals were transformed from a tetragonal to rhom-bohedral structure. The film deposition rates were 100 to 1000 Å/min, i.e., more than ten times those obtained by the conventional sputtering method.

Ferroelectric PbTiO3 thin films were prepared by a simultaneous deposition of TiO2 and PbO on heated substrates under the reduced pressure of 6 Torr. Titanium tetraisopropoxide and tetraethyl lead were used as source materials. The deposition behaviors of TiO2 and PbO were examined independently. Homogeneous nucleations of the reaction species in the vapor phase were depressed under the reduced pressure. The films obtained at 500° to 650°C of consisted of PbTiO3 of the single perovskite phase, and highly c-axis oriented and epitaxal films were grown on MgO(100). The deposition rate of the film available by adjusting the source temperature and the flow rate of the carrier gas is 50 to 1000Å/min, the maximum value of which is ten or more times that obtained by the conventional sputtering method.