Tomoyuki Yoshida

Photovoltaic Properties of Screen‐Printed CdTe / CdS Solar Cells on Indium‐Tin‐Oxide Coated Glass Substrates

Screen-printed CdTe/CdS solar cells were fabricated on glass and indium-tin-oxide (ITO) coated glass substrates, and their photovoltaic and electrical properties were analyzed. The CdTe/CdS/ITO cells showed efficiencies of 8.6--8.9%, a level which is 1--4% higher than efficiencies of cells without ITO. The higher efficiencies were caused by higher fill factor (FF) values. However, the FF values of the CdTe/CdS/ITO cells are considerably lower than those expected from the relatively low sheet resistances (11--13 {Omega}/{open_square}) of the CdS/ITO window layers. Further, the CdTe/CdS/ITO cells showed lower open-circuit voltages and unimproved short-circuit current densities when compared with the cells without ITO. This was evident despite the high transmittances of the CdS/ITO window layers relative to those of the CdS window layers over the wavelength range from 520 to 900 nm. The electrical analyses indicated that the lower photovoltaic parameters of the CdTe/CdS/ITO cells originated from a degraded junction, possibly due to the diffusion of the elements (In, O, and Sn) from the ITO layer through the CdS layer into the junction region.

Analysis of Photocurrent in Screen‐Printed CdS / CdTe Solar Cells

In this paper spatial photocurrent distribution in screen-printed CdS/CdTe solar cells are investigated using the light-beam-induced current (LBIC) technique. Furthermore, losses in short-circuit current density (J[sub sc]) have been analyzed through measurements of illuminated current-voltage characteristics, spectral responses, and reflectance spectra. The LBIC measurements revealed that the p-n junction area of the cell extended beyond the edge of a carbon (C) electrode on a CdTe film, but that the active area corresponded to the CdS/CdTe junction area covered with the C electrode. The photocurrent distribution in the active area was nonuniform. Its fluctuation increased with the CdS film thickness, without being affected appreciably by voltage and white-light biases. These results indicate that the fluctuation originated mainly from inhomogeneities of the CdS film. From the optical analysis of the J[sub sc], the improvement in CdS film quality proved essential for the increase of J[sub sc].

Preferred Orientation in Ti Films Sputter-Deposited on SiO2 Glass: The Role of Water Chemisorption on the Substrate

Ti thin films have been grown on SiO2 glass layers at 350°C by ultrahigh vacuum magnetron sputtering with a small amount of H2O, H2 or O2 gas introduction to investigate the influence of adsorption on the crystallographic orientation of the Ti films. In situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD) studies showed that a water vapor introduction at the beginning of sputter deposition promotes a highly preferred (002) orientation, whereas H2 gas or O2 gas introduction does not affect the orientation. These results indicate that the increase of water chemisorption on the substrate by H2O gas introduction and reduction of the surface free energy enhance the self-assembly of the Ti atoms toward the most stable C-axis orientation.

Effect of H2O partial pressure and temperature during Ti sputtering on texture and electromigration in AlSiCu/Ti/TiN/Ti metallization

The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO/sub 2//Si substrates has been investigated. The Ti(002) and TiN(111) preferred texture of the films deposited at 350°C was improved drastically by increasing the H/sub 2/O partial pressure from lxl0-9 to 3xi0-8 Torr. Both the Ti(002) and TiN(lll) texture showed a similar H/sub 2/O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti(002) texture was attributed to the self-assembly of Ti atoms on the SiO/sub 2/ surface, which had a low surface free energy due to the formation of surface OH groups. The AlSiCu/Ti/TiN/Ti film fabricated with the highly-textured TiN/Ti film showed a strong Al(111) texture and had a smooth surface. Moreover, interconnects from this improved film had longer EM lifetimes.

A Method to Detect Oxygen Precipitates in Silicon Wafers by Highly Selective Reactive Ion Etching

This work presents a new method for detecting oxygen precipitates in Si wafers. The method utilizes a highly selective reactive ion etching process. When a Si wafer containing oxygen precipitates is etched under the condition of high selectivity of silicon over silicon oxide, needle-shaped silicon cones can be formed below the oxygen precipitates, because they are hardly etched. Using this method, the depth distribution of the oxygen precipitates having diameters of at least 15 nm has been successfully evaluated by evaluating the number and height of the cones. It was also demonstrated that this method is effective in detecting oxygen precipitates remaining in the denuded zone.

Effect of water absorption of dielectric underlayers on crystal orientation in Al–Si–Cu/Ti/TiN/Ti metallization

The influence of the exposure of underlying dielectric (phophosilicate glass and borophosphosilicate glass) films to a humid air ambient on crystallographic orientations in Al–Si–Cu/Ti/TiN/Ti layered structures has been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered structures was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum value of an Al(111) x-ray rocking curve reached less than 1°. It was also found that the Al–Si–Cu surface becomes smoother and the average grain size increases as the Al(111) orientation improves. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. The mechanism of the improved Ti(002) orientation was investigated. It was confirmed that the improved orientation is closely related with the surface concentration of the absorbed water in the dielectric films. Further, it was demonstrated that interconnects fabricated from the improved layered structure have excellent electromigration performance.The influence of the exposure of underlying dielectric (phophosilicate glass and borophosphosilicate glass) films to a humid air ambient on crystallographic orientations in Al–Si–Cu/Ti/TiN/Ti layered structures has been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered structures was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum value of an Al(111) x-ray rocking curve reached less than 1°. It was also found that the Al–Si–Cu surface becomes smoother and the average grain size increases as the Al(111) orientation improves. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. The mechanism of the improved Ti(002) orientation was investigated. It was confirmed that the improved orientation is closely related with the surface concentration of the absorbed water in the dielectric films. Furth...

Influence of water absorption of dielectric underlayers on Al(111) crystallographic orientation in Al-Si-Cu/Ti/TiN/Ti layered structures

The influence of the exposure of underlying dielectric (phosphosilicate glass [PSG] and borophosphosilicate glass [BPSG]) films to a humid air ambient on crystallographic orientations in AlSi-Cu/Ti/TiN/Ti layered structures has been investigated as a function of the boron content and exposure time of the dielectric films. The Al( 11 1) orientation in the layered structures was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum (FWHM) value of an Al( 11 1) x-ray rocking curve reached less than 1 degree. It was also found that the Al-Si-Cu surface becomes smoother and the average grain size increases as the Al( I1 1) orientation improves. The improved Al( 1 1 1) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. The mechanism of the improved Ti(002) orientation was investigated. It was confirmed that the improved orientation is closely related with the surface concentration of the absorbed water in the dielectric films. Further, it was demonstrated that interconnects fabricated from the improved layered stmcture have excellent electromigration performance.

Electron cyclotron resonance light source from TE011 mode microwave plasma

An intense ultraviolet and visible radiation source for various applications has been conceptualized, designed, and developed using a TE011 mode microwave cavity filled with plasma immersed in a magnetic field. The radiation intensity emitted from the source, as a function of the magnetic field intensity, approaches maximum at the electron cyclotron resonance. Light intensity increases with pressure inside the Hg+Ar lamp and the microwave power.

Effect of water adsorption on Ti film initial growth on SiO2 surface

Abstract The initial growth processes of Ti thin films on water adsorbed SiO 2 surfaces have been compared with those on clean SiO 2 surfaces by means of Auger electron spectroscopy (AES). The oxidation of the deposited Ti atoms and the reduction of the SiO 2 surfaces were observed for both surfaces in the initial stage of the deposition. It was found that the reduction of SiO 2 surface was suppressed on water adsorbed SiO 2 surface. This restraint of the reaction at the initial stage of the growth is attributed to the stabilization of the SiO 2 surface by chemisorbed water. The growth modes of Ti thin films were suggested to be Stranski–Krastanov (SK)-like growth modes for both clean surfaces and water adsorbed surfaces.

Texture and electromigration lifetime improvements in layered Al-alloy metallization with underlying Ti by controlling water adsorption on SiO2 substrates

Abstract The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO 2 /Si substrates has been investigated. The Ti(002) and TiN(111) preferred texture of the films deposited at 350°C was found to be improved drastically by increasing the H 2 O partial pressure from 1×10 −9 to 3×10 −8 Torr. Both of the Ti(002) and TiN(111) textures showed a similar H 2 O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti(002) texture was attributed to the self-assembly of Ti atoms on the SiO 2 surface, which had a low surface free energy due to the formation of surface OH groups. Two kinds of layered Al-alloy interconnects, AlSiCu/Ti/TiN/Ti and AlCu/TiN/Ti, were fabricated with the highly textured TiN/Ti film, and their Al(111) texture and electromigration lifetime were then evaluated. It was confirmed that both of the interconnects have strong Al(111) texture and longer EM lifetimes.