Yuzo Shigesato

Electrical and structural properties of low resistivity tin-doped indium oxide films

Tin‐doped indium oxide (ITO) films with the resistivity less than 1.35×10−4 Ω cm were formed by low voltage dc magnetron sputtering (LVMS) and highly dense plasma‐assisted electron beam (EB) evaporation using the arc plasma generator (HDPE). The structural properties of these films were investigated using x‐ray diffraction, scanning electron microscope, and electron spectroscopy for chemical analysis, in comparison with the films formed by conventional magnetron sputtering and EB evaporation, in order to clarify the key factors for low resistivity. With decreasing plasma impedance and sputtering voltages from 540 to 380 V, the resistivity of the films deposited at Ts=400 °C decreased from 1.92 to 1.34×10−4 Ω cm, due mostly to increase in the carrier density. This LVMS film showed higher crystallinity because of lower damages of high‐energy particles during the deposition, which might increase the number of electrically active species. For HDPE, the film with resistance of 1.23×10−4 Ω cm was deposited at T...

A microstructural study of low resistivity tin-doped indium oxide prepared by d.c. magnetron sputtering

The microstructure of low resistivity (∼ 2 × 10−4 Ω cm) Sn-doped In2O3 (ITO) thin films prepared by multipass d.c. magnetron sputter deposition with an ITO (10 wt.% SnO2) target onto soda-lime glass substrates was investigated using plan-view and cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction. Each pass of the multipass sputter process deposits a 110 nm thick ITO layer. The substrate temperature was 400 °C during deposition and the sputter chamber was back-filled to a pressure of 1 × 10−3 Torr with a mixture of Ar and 0.8–1.0 at.% O2. Plan-view TEM studies combined with SEM observations of the film surface reveal that the sputtered ITO possesses a polycrystalline structure in which 200–350 nm grains are subdivided into highly oriented regions 10–30 nm in diameter. X-ray diffractometry studies show that the as-deposited films have a strong 〈100〉 texture and cross-sectional TEM studies reveal prominent columnar growth in the through-thickness direction.

Study of the effect of Sn doping on the electronic transport properties of thin film indium oxide

High quality, low resistivity (2.6×10−4 Ω cm), 0.32‐μm‐thick amorphous and polycrystalline, pure and Sn‐doped, In2O3 films prepared by high density plasma‐assisted electron beam evaporation were used to investigate the effect of Sn doping on the electronic transport properties of this material. Amorphous films with high carrier density in the as‐deposited state showed no effect of Sn doping on resistivity (ρ), Hall mobility (μ), or carrier density (n) over the range 0 to 5.3 wt % Sn. After recrystallization by annealing in air at 180 or 250 °C for 20 min, n, μ, and ρ were seen to be strongly dependent on Sn concentration in the range 0 to 1.5 wt % with a decreasing effect of Sn doping in the range 1.5 to 5.3 wt %. The data presented in this study were analyzed based on charged and neutral impurity scattering models and suggest that increasing Sn concentration leads to the formation of defect complexes which act as scattering centers but which do not contribute carriers to the material.

Origin of characteristic grain-subgrain structure of tin-doped indium oxide films

The microstructures of polycrystalline and heteroepitaxial tin-doped indium oxide (ITO) thin films prepared by sputtering and electron beam (EB) evaporation were investigated by electron microscopy, X-ray diffraction and reflection high-energy electron diffraction. The sputter-deposited ITO film on a glass substrate revealed a polycrystalline structure of grain size 400–800 nm. Within each grain, there were oriented subgrain regions 10–40 nm in size. This is a so-called “grain-subgrain structure” characteristic of sputter-deposited polycrystalline ITO films. These grains in sputter-deposited ITO films (“grain-subgrain structure”) were classified into three groups according to the morphology of the subgrains. The grains consisted of square, triangular and rectangular-shaped subgrains respectively. These three kinds of grain were oriented with the <400≫, <222≫ and <440≫ axes normal to the substrate surface respectively. It was also revealed that the film thickness of these three kinds of grain decreased in the order of the grains consisting of <400≫-, <222≫- and <440≫-oriented subgrains. However, heteroepitaxial ITO films sputtered on yttria-stabilized zirconia (YSZ) substrates, and EB-evaporated ITO films on both glass and YSZ substrates showed different structures. By comparing the microstructures of polycrystalline films with those of heteroepitaxial films, the origin of the above-mentioned “grain-subgrain structure” (variation of shapes and thickness of the subgrains) was described on the basis of the crystalline-plane-dependent resputtering rate of ITO films during sputter deposition. The resputtering rate during sputter deposition of ITO films is considered to be dependent on the crystalline planes of ITO and increases in the order of the (400), (222) and (440) planes.

Visible photoluminescence from nanocrystalline Ge formed by H2 reduction of Si0.6Ge0.4O2

Samples of nanocrystalline Ge embedded in SiO2 that display visible photoluminescence were synthesized from chemical vapor deposition‐grown Si0.6Ge0.4 in a two step process of hydrothermal oxidation using steam at 25 MPa and 475 °C followed by annealing at 750 °C in flowing forming gas (80/20:N2/H2). A broad photoluminescence band, peaked at 2.14 eV (580 nm) with a full width at half maximum of 0.3 eV, was observed in samples that were annealed at 750 °C in flowing forming gas for 10, 30, and 60 min. As‐oxidized (i.e., unprecipitated) samples show no photoluminescence peak when excited under identical conditions.

Electrical and Structural Properties of Tin-Doped Indium Oxide Films Deposited by DC Sputtering at Room Temperature

Tin-doped indium oxide (ITO) films were deposited on soda-lime glass plates without substrate heating by dc magnetron sputtering. Crystallinity and electrical properties of the films were investigated by X-ray diffraction and Hall-effect measurements, which showed clear dependence on target–substrate distance (T–S) and on total gas pressure (Ptot) during deposition. Degradation in crystallinity was observed at relatively high or low Ptot, where the upper or lower Ptot level for depositing films with high crystallinity was increased with decreasing T–S. Based on a hard sphere collision model, the crystallinity of the films was considered to be strongly affected both by the kinetic energy of sputtered In (or Sn) particles and by the bombardment of high energy particles arriving at the growing film surface. The former could enhance the crystallinity, whereas the latter degraded both the crystallinity and conductivity. Such degradation in electrical properties was mainly due to a decrease in carrier density.

Study of the effect of ion implantation on the electrical and microstructural properties of tin-doped indium oxide thin films

Ion implantation of H2+ or O+ ions in the range 0–1.7×1015 and 0–1.3×1015/cm2, respectively, was used to investigate the effect of implant‐induced damage on the electrical properties of Sn‐doped In2O3 (ITO) films deposited by electron‐beam evaporation on SiO2‐coated soda‐lime glass substrates. The films were characterized as a function of implant dose using low‐temperature Hall effect, resistivity, optical transmissivity, x‐ray diffraction, and transmission electron microscopy (TEM). A systematic decrease in both carrier density (n) and Hall mobility (μ) was observed with increasing dose of either implant species. The electronic results were analyzed using charged and neutral impurity scattering models which suggest that the observed changes are due to the degradation of electrically active donor centers and the generation of the neutral scattering centers. The microstructure of the implanted films, as revealed by TEM and x‐ray diffraction, is consistent with the presence of significant dynamic recovery d...

Doping mechanisms of tin‐doped indium oxide films

The polycrystalline Sn‐doped In2O3 (ITO) films with different Sn concentrations of 0–6.7 wt% (SnO2 wt%) were prepared by postannealing the amorphous ITO films deposited by highly dense plasma‐assisted EB evaporation at the low substrate temperature. These films were confirmed to show the high crystallinity and homogeneous Sn distribution by x‐ray diffraction (XRD), scanning electron microscopy, and electron spectroscopy for chemical analysis. The detail XRD pattern of 1.9 wt% Sn concentration film showed the doublet peaks, indicating that the film structure was the mixture of two different lattice parameters (LP); one was +0.18% larger and another was −0.13% smaller than the In2O3 LP, which could be attributed to the interstitial and the substitutional Sn atoms, respectively.

Crystallinity and electrical properties of tin-doped indium oxide films deposited by DC magnetron sputtering

Abstract ITO films with thickness s between 1000 and 8000Awere deposited on glass substrates at 400°C by DC magnetron sputtering. The electrical and structural properties were compared to the same properties in evaporated ITO films and ITO powder using ESCA, SEM and X-ray diffraction. The resistivity decreased from 1.92 × 10−4 to 1.46 × 10−4 Ω cm as the thickness increased from 1140 to 7620A, due mostly to a monotonic increase in the carrier density. The (400) plane spacing in the films was higher than in pure In2O3 powder. However, the difference between the (400) plane spacings in the In2O3 and the films decreased as the film thickness increased, from 0.87% in an 1140Athick film to 0.54% in a 7620Athick film. For an EB evaporated ITO film having a thickness of 3860A, the spacing was 0.24% larger than in pure In2O3. X-ray diffraction analysis based on the integral breadth method demonstrated a clear positive correlation between random strain and uniform strain. The decrease of strain and of lattice constant with increasing thickness led to the conclusion that the increased carrier density in thicker films is due to an improvement in crystallinity, which leads to a higher density of electron donor centers.

Emission spectroscopy during direct‐current‐biased, microwave‐plasma chemical vapor deposition of diamond

Optical emission spectroscopy was used to investigate dc biasing during diamond film synthesis in a microwave plasma. These measurements show that biasing produces significant changes near the substrate (i.e., close to the sheath region). Increasing the negative bias voltage (Vb) from 0 to −180 V in a CH4/H2/Ar (4/496/30 sccm) mixture increases the intensities of the hydrogen Balmer α and β lines. The relative concentrations of neutral atomic hydrogen were estimated by using an Ar(750.4 nm) emission line as an actinometer. At 38 Torr, increasing Vb from 0 to −150 V increased the concentration of atomic hydrogen by more than 20%. In addition, increasing Vb also increased the electron temperature near the substrate. These effects are likely to play an important role in the enhanced diamond nucleation that has been observed after negative‐biased pretreatment.