Tadatsugu Itoh

Backscattering measurements on Ag photodoping effect in As2S3 glass

350‐keV He+ backscattering analysis was applied to the investigation of Ag photoinduced diffusion into As2S3 glass and proved to be suitable for the present purposes. Silver atoms diffuse into As2S3 by photoirradiation (termed ’’photodoping’’). Photodoped Ag concentration is nearly uniform and falls abruptly beyond a certain depth. The concentration of S in the photodoped region is nearly equivalent to that in As2S3. Preirradiation of As2S3 before Ag deposition enhances Ag diffusion, which results in a tailing of the Ag concentration. The preirradiation effect disappears after a long period. Thermal diffusion of materials was also investigated for comparison.

Effect of Si‐Ge buffer layer for low‐temperature Si epitaxial growth on Si substrate by rf plasma chemical vapor deposition

Silicon epitaxial growth on the Si‐Ge buffer layer at a low substrate temperature by the rf plasma chemical vapor deposition using SiH4 and GeH4 has been investigated. The electron Hall mobility of the homoepitaxial layer grown at 750 °C with a growth rate of 14 A/sec coincides with that of bulk Si, but for a high growth rate of 33 A/sec, the mobility was limited to within half the value of bulk Si. However, a small amount of Ge introduced in an initial stage of growth to form the Si‐Ge buffer layer improved the crystalline quality of the ensuing Si epitaxial layer with a high growth rate. The electron Hall mobility of the Si layer grown on the Si‐Ge buffer layer was a similar value of bulk Si in a low carrier concentration of 6×1015 cm−3. The crystalline quality of the grown Si layers was examined by the combination of Rutherford backscattering spectrometry and transmission electron microscopy.

Low Temperature Silicon Epitaxy by Partially Ionized Vapor Deposition

Silicon films were formed on single crystal silicon substrates by partially ionized vapor deposition. Single crystal films were obtained on (111) p-type silicon substrates at room temperature when the silicon ion current density, which was about 25% of the total incident silicon atoms, exceeded 80 µA/cm2. Anneal behaviors of epitaxial films grown at room temperature and 400°C at an ion current density of 100 µA/cm2 were investigated by He+ backscattering measurements and by measurement of change in resistivity.

Porous silicon layers and its oxide for the silicon‐on‐insulator structure

Crystalline properties of Si films grown on porous Si layers were investigated. Based on the results obtained by Rutherford backscattering spectroscopy and cross‐sectional transmission electron microscopy, a model of Si epitaxial growth on a porous Si layer is proposed. In our model dominant defects in the region near the epitaxial layer/porous Si interface and in the one near the surface in the epitaxial layer are dislocations and stacking faults, respectively. The oxidation rate of the porous Si layers is about 80–130× faster than that of the bulk Si, and the etching rate of the oxidized porous Si layers is almost equal to that of the bulk oxide. The effective dielectric constants of the oxidized porous Si layers have a close relation to the anodic current density, ranging from 3.8 to 4.0.

Arsenic Vacancy Formation in GaAs Annealed in Hydrogen Gas Flow

From results of the photoluminescence studies of heavily Si-doped n-type GaAs, which have followed ion implantation at 70 kV with Ar+, As+, and O+ and/or annealing at 800°C in hydrogen gas flow, it is confirmed that a luminescence line near 1.4 eV which has a half-width of about 80 meV at 80 K is attributed to a SiAs–VAs, complex, in which a hole is not tightly bound to the complex center. Arsenic vacancy could be satisfactorily reduced by arsenic-implantation if the arsenic dose and energy are appropriately chosen. In Si-doped GaAs, an oxygen atom occupies an arsenic site if it is empty, otherwise the oxygen atom stays at an interstitial site and joins a silicon atom.

DOPING OF SILICON BY ION IMPLANTATION

Radiation damages created in silicon single crystals bombarded with 10‐keV aluminum ions were examined by means of electron diffraction method. A deep penetration of aluminum ion in silicon was observed, extending to 0.58 μ. This penetration was depressed by removing the bombarded surface layer about 800 A in thickness before annealing. From these results, we interpret the deep penetration as a radiation enhanced diffusion effect.

Arsenic and Cadmium Implantations into n‐Type Gallium Arsenide

Electrical properties of cadmium‐implanted layers in n‐type GaAs substrates and effects of arsenic preimplantations have been investigated. The implant conditions were energy 20 keV, dose 1014–1016/cm2, and substrate temperature 500°C for cadmium implants and 25°C for arsenic preimplants. The measured carrier‐concentration profile shows that a heavily doped p‐type layer exists within 1000 A of the surface for cadmium‐implanted specimens. However, current‐voltage and capacitance‐voltage characteristics of the diodes fabricated by implantations of 1015 and 1016 Cd/cm2 indicate that these junctions have a p‐π‐n structure. Thicknesses of the π layers are about 3 μ for the dose of 1016 Cd/cm2 and 1.5 μ for 1015 Cd/cm2. On the other hand, diodes fabricated by arsenic and cadmium implants have characteristics of normal p‐n junctions. Arsenic preimplantation reveals the fact that high‐dose implantation into a hot substrate produces a large number of arsenic vacancies, which diffuse deeply into the substrate. Arse...

Isolation of silicon film grown on porous silicon layer

We have investigated a new technology for dielectric isolation of a Si film grown epitaxially on a porous silicon layer. After oxidation of the porous silicon layer, a Si on Ohcidized Porous Silicon(SOPS) structure can be obtained. It is proposed that micropores pinch off quickly in the interfacial region between the porous silicon layer and the epitaxial film. A minimum yield calculated from Rutherford backscattering spectra of the epitaxial silicon film is 5.3%, and an electron Hall mobility of 600cm2/V.s is obtained in the film with a carrier concentration of 1 x 1017 /cm3. MOSFETs were fabricated on the SOPS structure.

Epitaxial growth of Si–Ge layers on Si substrates by plasma dissociation of SiH4 and GeH4 mixture

Silicon–germanium epitaxial layers were formed on (111) oriented Si substrates by the plasma dissociation of a mixture of SiH4 and GeH4. A growth rate of 33 A/sec was obtained at a substrate temperature of 750 °C for Si–Ge epitaxial growth using 1×10−2 Torr of SiH4 and 1×10−4 Torr of GeH4 mixture as source materials. The introduction of GeH4 to SiH4 provided a good nucleation for epitaxy. Less than 1% of GeH4 is sufficient to reduce the concentration of the crystalline defects such as voids which form in the epitaxial layers at low substrate temperature with a high growth rate. The electron Hall mobility of layers coincided with that of bulk Si in the temperature range between 77 °K and room temperature.

Ga(AsP) light‐emitting diode formed by ion implantation

Hot ion implantation as a doping technique was used for the fabrication of visible‐light‐emitting diodes with GaAs1−xPx(x = 0.38 ± 0.01). Zinc ions, p‐type dopants, were implanted into n‐type (001)‐oriented heteroepitaxially grown Ga(AsP)‐on‐GaAs substrates at 400°C with an energy of 20 keV. Then, thermal treatment at various temperatures was carried out on the sample in order to investigate the effect of annealing on the electrical properties of Zn‐implanted layers in the Ga(AsP) substrate. The p‐type layer, which was obtained by the ion implantation of 2 × 1015 Zn ions/cm2 with subsequent annealing at 900°C for 40 min, was found to have an effective surface concentration of 1.7 × 1015 carriers/cm2 and a sheet resistivity of about 100 Ω/sq. Red‐light‐emitting Ga(AsP) diodes fabricated using Zn ion implantation have usually shown an average brightness of 400–600 fL, and sometimes as high as 850 fL at a current density of 10 A/cm2. Diodes, which were formed by means of a standard Zn diffusion technique in ...