K. Kuriyama

Single crystal growth and characterization of LiInSe2

Abstract LiInSe 2 single crystals were grown by directional solidification. The typical as-grown crystal has dimensions of about 20 mm length and 10 mm diameter and shows a deep red color. The lattice constants were determined to be a = 7.218 A, b = 8.441 A, and c = 6.772 A by powder X-ray diffraction. The easiest cleavage plane was estimated to be the b -face. The melting point was determined by differential thermal analysis to be 904°C. The energy band gap of LiInSe 2 at room temperature was estimated by optical transmission measurements to be 1.88 eV. Typical room temperature electrical resistivity was 2.67 × 10 11 Ω cm with n-type conductivity.

Characterization of epitaxial (Y,Bi)3(Fe,Ga)5O12 thin films grown by metal-organic decomposition method

Epitaxial (Y,Bi)3(Fe,Ga)5O12 garnet thin films have been prepared on Gd3Ga5O12 (111) substrates by a metal-organic decomposition (MOD) method using carboxylic acids. The chemical compositions of the films prepared in this study are Y2BiFe5O12 (YBFO), Y3Fe4GaO12 (YFGO), and Y2BiFe4GaO12 (YBFGO). Epitaxy of these films was confirmed by x-ray diffraction and Rutherford backscattering (RBS) measurements. Full width of half maximum values of the 444 diffraction peaks of YFGO and YBFGO were 0.4° and 0.04°, respectively. RBS channeling was clearly observed for the YFGO film with a minimum yield χmin along the [111] direction of ∼7.5%. These garnet films could also be reproducibly obtained by the MOD method without any deterioration in the MOD solutions over two years.

Dielectric constants and bond parameters of LiInSe2 and LiGaSe2

The dielectric constants of two lithium ternary chalcogenides, LiInSe2 and LiGaSe2, are obtained to be 8.45 and 8.75, respectively, by capacitance measurements at room temperature. The temperature dependence of dielectric constants of both crystals show linear increase with temperature over the range 77–300 K. The temperature coefficients for LiInSe2 and LiGaSe2 are 2.90×10−4 and 3.80×10−4 K−1, respectively. The bond parameters of LiInSe2 and LiGaSe2 are obtained using the Phillips‐Vechten’s and Levine’s dielectric model. The bond characteristics are discussed within the concepts of ionicity and transverse effective charge.

Lattice distortions and the transmuted-Ge related luminescence in neutron-transmutation-doped GaN

The lattice distortion and the transmuted-Ge related luminescence in neutron-transmutation-doped (NTD) GaN are studied by combining Rutherford backscattering spectroscopy/channeling, Raman scattering, and photoluminescence methods. The lattice displacement of Ga atoms of ∼0.12 A from the 〈0001〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-irradiated GaN with a minimum yield (χmin) of 7%. A 2.84 eV emission band observed in 600 °C annealed NTD-GaN is associated with the Ga interstitial, supporting the lattice distortion. Two emission bands at 2.90 eV and 2.25 eV observed in 1000 °C annealed NTD-GaN are assigned to a negatively charged DX-like center of Ge at Ga site and a complex defect attributed to Ge at Ga site and Ga vacancy, respectively.

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...

Annealing effects on electrical properties of LiInSe2

The electrical properties of LiInSe2 single crystals are presented. As‐grown LiInSe2 crystals have n‐type conductivity and high electrical resistivity (1011 W cm at room temperature). Annealing in selenium atmosphere leads to p‐type crystals having lower resistivity (105 W cm at room temperature). The origin of donors and acceptors in LiInSe2 are discussed through the annealing study. The energy band gap is estimated from the results of electrical resistivity measurements to be 1.91 eV. The value is supported by the optical transmission. A simple band diagram is proposed consequently.

Hundred-micron-sized all-solid-state Li secondary battery arrays embedded in a Si substrate

Fabrication and charge/discharge behaviors of all-solid-state Li secondary battery arrays embedded into three Si trenches of 200×100 μm2 in area and 0.5∼2.0 μm in depth are presented. The battery arrays in a Si wafer, consisting of multiple layers (Al current collector/Li/SiO2–15 at. %P2O5/LiMn2O4/polycrystalline silicon current collector), are prepared by combining a sol-gel spin-coating method and Si very-large-scale integration technologies. Porous spin-on glass (SiO2–15 at. %P2O5) is adopted as an electrolyte layer, in which spatial paths for Li+ ions are artificially introduced into the glass. Each active battery area is isolated with double insulating walls (Si3N4/SiO2). The battery arrays demonstrate a constant capacity of ∼9.2 μA h cm−2 at ∼3.6 V up to 100 cycles.

Sol–gel growth of LiCoO2 films on Si substrates by a spin-coating method

LiCoO 2 films are prepared on Si substrates by a sol-gel growth method. Two raw materials, Li acetate (99%) and Co (99%) acetate, are mixed in the atomic ratio Li:Co of 1:1 and dissolved in methanol together with citric acid as a chelating agent. The stoichiometory of the raw materials is more severely required for the preparation of a single-phase LiCoO 2 . The raw materials spin-coated on Si substrates are annealed at various temperatures (300-800°C) for 30 min under O 2 flow. The structural identification is performed using X-ray diffraction and Raman scattering methods. These results show that the structural transformation from the spinel structure to the layered-rock-salt one occurs at 600°C.

Observation of the crystal-field splitting related to the Mn-3d bands in spinel-LiMn2O4 films by optical absorption

Mn 3d bands in spinel-LiMn2O4 films, synthesized on SiO2-glass substrates by a sol-gel method, were studied using an optical absorption method. Two absorption peaks were observed at around 1.63 and 2.00 eV at room temperature. These peaks were associated with two d–d transitions: One is the Mn t2g to the lower Mn eg bands transition and the other the Mn t2g to the upper Mn eg bands one. A large absorption was also observed above 3.0 eV, indicating a transition from the O 2p valence band to the Mn 3d bands. The d–d transitions showed the blueshifts of 20–30 meV at 77 K comparing with those at room temperature. The observed electronic structure was consistent with the calculated one.

Ion channeling effect of In dopant in semi‐insulating GaAs

The channeling phenomena of undoped and In‐doped semi‐insulating GaAs grown by the liquid encapsulated Czochralski method have been analyzed by 1.5 MeV 4He+beam. It is suggested that the minimum yield of backscattering particles is affected by the local lattice distortion due to the addition of large amounts of In atoms rather than the difference in dislocation density. It is also indicated that the In atoms of ∼1020/cm3 doped in GaAs occupy substitutional sites within the statistical errors.