Takashi Ehara

Electron paramagnetic resonance studies on microcrystalline silicon prepared by sputtering method

Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (μc-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the μc-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the μc-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects.

The effect of nitrogen doping on the structure of cluster or microcrystalline silicon embedded in thin SiO2 films

In this study, we investigated the effects of nitrogen doping on the structural properties of cluster or microcrystalline Si embedded in thin SiO2 films. Thermal annealing of Si-rich a-SiOx or a-SiOxNy (x > y) films prepared by the r.f. co-sputtering method produces Si clusters or microcrystallines in the films. The structure of the embedded Si grains is affected by nitrogen doping that is achieved by using Ar-N2 mixed gas as the sputtering gas. Nitrogen doping decreases the size of the Si grains after the thermal annealing process. We were able to observe this decrease of the crystallite size clearly by using the Raman spectra as a peak shift. Our analysis of the IR absorption of the Si-O-Si bond revealed the prevention of the migration reaction of Si and O atoms by nitrogen doping. This effect of doped nitrogen decreases the size of the Si crystals after the annealing process.

The crystalline properties of nitrogen doped hydrogenated microcrystalline silicon thin films

The crystalline properties of nitrogen doped hydrogenated microcrystalline silicon thin films deposited by plasma enhanced chemical vapor deposition were studied. Gas phase doping density in the order of 10−2 and 10−1 leads to changes in the crystalline properties of the films. Raman scattering signals indicate that nitrogen doping causes a more significant reduction in crystallite size than does an increase in SiH4 concentration. In addition, the size reduction occurs with a less significant increase in amorphous fraction volume than in the case of SiH4 concentration increase. The N in the Si crystalline induces disorder or stress as a result of the higher electronegativity and smaller atomic size of N compared to Si. Thus, the crystallite size reduction is thought to occur to reduce the disorder in crystalline grain induced by doped nitrogen.

Multi-band electron paramagnetic resonance study of the defects in microcrystalline silicon

Abstract We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (μc-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (μc-Si) film prepared by RF sputtering, and μc-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g=2.006 in the microcrystalline fraction of the μc-Si, μc-Si:H and μc-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the μc-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values.

Electron spin resonance study of nitrogen-doped microcrystalline silicon and amorphous silicon

The neutral silicon dangling bond (DB) defect and conduction electron properties of nitrogen-doped silicon film deposited by use of highly diluted silane gas were studied using electron spin resonance. At lower gas phase doping density, film come to have a microcrystalline silicon (μc-Si:H) structure, and the resonance peaks of DB and conduction electron spin resonance (CESR) was observed. As intensity of CESR showed significant dependence on doping density, nitrogen was confirmed to function as an electron donor. In contrast, highly doped samples became amorphous and only the DB was detected. Although in μc-Si:H the DB peak showed little dependence on nitrogen doping density, a-Si:H film exhibited dependence on doping density in both g value and signal width.

Nitrogen-Doping Effects on Electrical Properties of Hydrogenated Microcrystalline Silicon as Studied by Electron Paramagnetic Resonance and Conductivity

We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

Crystalline orientation control in sol-gel preparation of CuAlO2 thin films

Thin films of CuAlO2 were prepared by the sol–gel method using Cu acetate and Al acetate as starting materials. Films prepared using a sol with a total metal ion concentration of 0.40 M and gel preparation conditions with a post-coating heat treatment higher than 400 °C displayed crystallinity with significant c-axis orientation after annealing at 850 °C in N2. Almost no X-ray diffraction peaks beside the c-axis-oriented peaks were observed. In contrast, films prepared using a sol with higher metal ion concentration showed non-c-axis-oriented X-ray diffraction peaks of CuAlO2 in addition to c-axis-oriented peaks. It is found that dip-coating using a sol with an adequately low total metal ion concentration followed by post-coating heat treatment at an adequately high temperature produce the gel films that contain microcrystalline CuO. It is considered that the gel films that contains microcrystalline CuO with sufficiently thin thickness are appropriate to produce significantly c-axis-oriented CuAlO2 films after high-temperature annealing under nitrogen flow.Graphical Abstract

Preparation of phosphorous doping to beta-iron disilicide thin films and application for devices

In the present work, preparation and device applications of phosphorous doped /spl beta/-FeSi/sub 2/ are described. Optical bandgap and conductivity of undoped and phosphorus doped /spl beta/-FeSi/sub 2/ thin films prepared by RF sputtering are measured. In addition, typical current-voltage characteristics of phosphorous-doped /spl beta/-FeSi/sub 2//p-type Si substrate heterojunctions are shown.

Contact Resistivity and Adhesion of Ni/AuGe/Ag/Au Ohmic Contact Directly to n-Type AlGaAs

The direct ohmic contact to AlGaAs, Ni/AuGe/Ag/Au=5/120/100/580 nm has been studied. Contact resistivity of 3.8×10-5 Ω cm2 is obtained after thermal treatment for 10 min at 450° C. This is one order lower than that of the conventional Ni-Ge-Au system. The new metallization also indicates strong adhesion on SiNx film, does not peel off even after thermal treatment during all device processes and withstands the wire bonding process. We conclude that the metallization is useful and applicable for AlGaAs-related devices.

Preparation and structure of unhydrogenated microcrystalline silicon thin films by sputtering

Unhydrogenated microcrystalline silicon (μc-Si) thin films have been prepared by sputtering. The formation of the microcrystalline films was observed at the Ar sputtering pressure of 26.6 Pa by Raman spectra and X-ray diffraction. In addition, the increase of the sputtering pressure induces an increase of the crystallite size and a decrease of the growth rate.