Masataka Satoh

Intermediate Amorphous Layer Formation Mechanism at the Interface of Epitaxial CeO2 Layers and Si Substrates

The formation mechanism of an intermediate amorphous layer between epitaxially grown CeO2 layers and silicon substrates is studied using cross-sectional transmission electron microscopy and Auger electron spectroscopy. The intermediate amorphous layer thickness increases after annealing at 800°C in air, whereas it decreases somewhat after annealing in an ultrahigh vacuum. Auger in-depth analysis verifies that the intermediate amorphous layer is silicon dioxide. The intermediate oxide growth of the CeO2/Si structures due to intentional oxidation at 700~900°C in a dry oxygen ambient is analyzed and the results indicate that the oxidation proceeds in an intermediate step between reaction limited and diffusion limited processes. The intermediate amorphous layer formation mechanism is concluded to be oxygen diffusion through CeO2 layers and successive oxidation of silicon at the interface.

Electrical Characteristics of Metal/Cerium Dioxide/Silicon Structures

Electrical characteristics of a Au/CeO2/Si structure have been measured by means of capacitance-voltage (C–V) and conductance-voltage (G–V) methods. Single crystalline and polycrystalline CeO2 films are grown on silicon substrates using electron-beam evaporation. MOS characteristics of the samples are classified by the crystallinity of the CeO2 films rather than by the orientation or conduction type of the Si substrate. Polycrystalline CeO2 film samples show a fine structure around the flat-band voltage in the C–V curves and injection-type hysteresis. It is clarified that the characteristics of the single crystalline CeO2 film sample are free from such undesirable properties caused by negative charge and carrier injection. Dielectric constant er of the CeO2 films is estimated to be around 20, which is close to the bulk value (~26).

Photoluminescence study of the annealing behavior of transmuted impurities in neutron-transmutation-doped semi-insulating GaAs

In neutron‐transmutation‐doped GaAs irradiated with various fast neutron fluences, the annealing behavior of band‐germanium acceptor [Ge(B‐A)] transitions has been evaluated using the photoluminescence technique. In the fast neutron irradiation of ≤7.0×1017 cm−2, a few percent of transmuted Ge atoms behave as acceptors in As sites and more than 98% of the transmuted Ge atoms activate as donors in Ga sites. In the fast neutron irradiation of 3.7×1018 cm−2, the shift of Ge(B‐A) transitions towards lower energies originates from the band‐edge distortion. Removing the band‐edge distortion by annealing above 790 °C leads to the increase in the Ge acceptor, accompanied by an increase of the peak intensity of Ge(B‐A) transitions. The lower electrical activation of transmuted impurities (∼75%) arises from the high‐temperature annealing required to remove the radiation damage. On annealing out the radiation damage, the peak shift of Ge(B‐A) transitions based on the increase in the free carrier is discussed using t...

Solid phase epitaxy of implantation-induced amorphous layer in (11̄00)- and (112̄0)-oriented 6H-SiC

The epitaxial regrowth of the implantation-induced amorphous layer in (1100)- and (1120)-oriented 6H-SiC has been investigated at annealing temperatures below 800 °C using Rutherford backscattering spectrometry and transmission electron microscopy. The surface region of sample is amorphized by the Ar+ ion implantation with an energy of 100 keV at a dose of 2×1015/cm2. The implantation-induced amorphous layer epitaxially regrows at annealing temperatures above 700 °C without the inclusion of other polytype crystals such as 3C-SiC and twinned defects. The regrowth rate is estimated to be about 0.4 nm/min at 700 °C and is proportional to the annealing temperature with an activation energy of about 3.4 eV for both (1100)- and (1120)-oriented 6H-SiC.

Low temperature epitaxial growth of CeO2(110) layers on Si(100) using electron beam assisted evaporation

Abstract With the aims of lowering growth temperature and improvement of crystalline quality, the effect of electron-beam assistance is studied in the epitaxial growth of CeO2(110) layers on Si(100) substrates by electron-beam evaporation in an ultrahigh vacuum. From experiments of evaporation at positive substrate bias, it is clarified that electron incidence onto the growing surface is effective in the facilitation of the epitaxial growth. Newly developed electron-beam assisted evaporation proves to have much greater effects in both the growth temperature lowering and the crystalline quality improvement. The epitaxial growth facilitation effect depends on incident electron energy. Optimum electron energy is determined to be around 360 eV, wherein the epitaxial temperature is lowered to 710 °C, i.e. temperature lowering of more than 100 °C compared with the conventional growth method.

Influence of photoexcitation on hopping conduction in neutron‐transmutation‐doped GaAs

The nature of the tunneling‐assisted hopping conduction in neutron‐transmutation‐doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 °C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (AsGa) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, AsGa≤1×1018 cm−3, consists of the coexistence of the hopping and band conductions.

Remarkable Reduction of On-Resistance by Ion Implantation in GaN/AlGaN/GaN HEMTs With Low Gate Leakage Current

We demonstrate Si ion-implanted GaN/AlGaN/GaN high-electron mobility transistors with extremely low gate leakage current and low source resistance without any recess etching process. The source/drain (S/D) regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into S/D regions with an energy of 80 keV, the performances were significantly improved. On-resistance decreased from 26.2 to 4.3 Omegaldrmm. Saturation drain current and maximum transconductance increased from 284 to 723 mA/mm and from 48 to 147 mS/mm.

The role of Ga antisite defect in the activation process of transmuted impurities in neutron‐transmutation‐doped semi‐insulating GaAs

In neutron‐transmutation doping for undoped and In‐doped GaAs irradiated with thermal and fast neutrons of 1.5×1018 and 7.0×1017 cm−2, we have found for the first time photoluminescence emissions around 860 and 935 nm at 77 K associated with the two difference levels of Ga antisite defect (GaAs). It is suggested that the annealing of GaAs defects plays an important role in the activation process of transmuted impurities as well as the annealing of As antisite defects forming midgap electron traps. The GaAs defects are annihilated in an annealing temperature range from 650 to 700 °C, accompanied by an abrupt decrease in resistivity.

Electron-beam-assisted evaporation of epitaxial CeO2 thin films on Si substrates

Electron-beam-assisted evaporation is a way to lower the growth temperature and improve crystalline quality of CeO2(110) layers on Si(100) substrates. The electron-beam-assisted evaporation system is constructed utilizing an electron-beam-irradiation system with a suppressor electrode around the sample holder. The suppressor bias condition is optimized as a function of acceleration energy of assisting electrons. The epitaxial growth quality depends on the assisting electron-beam energy. Optimum electron energy is experimentally determined to be around 360 eV, wherein the epitaxial temperature is lowered to 710 °C, i.e., temperature lowering of more than 100 °C compared with the conventional growth method.

Surface structure of single-crystal CeO2 layers grown on Si

Abstract The surface morphology of epitaxially grown CeO 2 layers on Si(100) and Si(111) substrates was studied using atomic force microscopy (AFM) and transmission electron microscopy. It was found that the CeO 2 (111)/Si(111) surface has a triangular-pyramidal hillock structure consisting of three (111) facets. In contrast, the CeO 2 layer grown on Si (100) has (110) orientation and a periodically corrugated structure with gable roof shaped stripes consisting of two (111) facets. Quantitative analyses of AFM data reveal that as the layer thickness increases, the surface structure grows in size: the surface roughness increases monotonically for CeO 2 (111), whereas it saturates for CeO 2 (110).