Akio Masuyama

Carrier dynamics at surface and interface in hydrogenated amorphous silicon observed by the transient grating method

Carrier dynamics at a free surface and an interface in a glow discharge hydrogenated amorphous silicon (a:Si:H) film were observed by a transient grating method. The diffusion coefficients and lifetimes at the surface and in the bulk were determined separately by exciting carriers by selecting the wavelength of the excitation light. The diffusion coefficients and lifetimes in the bulk, at the surface and interfaces decreased in the following order: bulk, a:Si:H free surface, a‐Si:H/substrate interface, a‐Si C:H/a‐Si:H interface.

The dynamics of photoexcited carriers in microcrystalline silicon

Dependences of the diffusion coefficient and the lifetime of photoexcited carriers in undoped microcrystalline silicon ( μc‐Si) on the volume fraction and the grain size were observed by a transient grating method and the dynamics of photexcited carriers is discussed. Under the condition of a constant grain size, the lifetime decreases with the increase of the volume fraction but the diffusion coefficient increases with the increase of the volume fraction for any fraction larger than 0.2. The dependence of the lifetime was explained well by a carrier recombination at grain boundary regions. The dependences of the diffusion coefficient and the dark conductivity were interpreted by a percolation process.

Study of optically induced degradation of conductivity in hydrogenated amorphous silicon by transient grating method

Optically induced degradation of the conductivity (the Staebler–Wronski effect) in glow discharge hydrogenated amorphous Si was examined by a transient grating method. It was clarified that the Staebler–Wronski effect was a bulk and not a surface effect, and the origin of the decrease of the photoconductivity was mainly attributed to the decrease of the lifetime instead of the mobility.

Steady‐state and time‐resolved photoluminescence in microcrystalline silicon

A systematic investigation has been made on steady‐state and time‐resolved photoluminescence (PL) in microcrystalline silicon (μc‐Si) at liquid‐helium temperature. The steady‐state PL spectra on various grain sizes and volume fractions are examined. It is found that the low‐energy emission (∼0.76 eV) arises only from the amorphous phase and not from the crystalline phase and the grain boundary regions. The results indicate that the origin of the luminescence is considered to be due to defects created in the amorphous phase resulting from the microcrystallinity which increase with the grain size and/or the volume fraction. It has been shown from the analysis of the time‐resolved PL measurement that the recombination transition of carriers of the low‐ and the high‐ (∼1.24 eV) energy emissions can be interpreted by a new model.

Maskless Ion Beam Assisted Etching of Si Using Chlorine Gas

Characteristics of maskless ion beam assisted etching of Si have been investigated as a function of chlorine gas pressure. Focused Ga ion beam was irradiated on a Si substrate in chlorine gas atmosphere at a pressure ranging from 0 to 24 mTorr. The etching rate exhibited a maximum at a pressure of 8 mTorr, the value of which was about 5 times larger than the physical sputter etching rate, and decreased at higher chlorine gas pressure. At a pressure of 8 mTorr, the chlorine atom arrival rate was about 4 times larger than the Si removal rate. This ratio suggests that Si is mainly removed by forming volatile SiCl4.

Maskless Etching of AN Using Focused Ion Beam

Maskless submicron etching of AN has been performed using ion beam assisted etching (IBAE) technique. 35 keV Ga focused ion beam and chlorine gas was used for the etching. Al target was prepared by evaporation on Si substrate. When the pressure of chlorine gas ambient was varied from 0 to 32 mTorr, the etching rate of Al exhibited a maximum value which was 4.3×10-5cm3mA-1min-1 at a pressure of 5 mTorr. This value was about 10 times larger than that of physical sputter etching. Chlorine contamination was found to be below detection limit by Auger analysis.

Diffusion of carbon atoms in hydrogenated amorphous silicon carbide into hydrogenated amorphous silicon through the interface

It was found that carbon atoms in hydrogenated amorphous silicon carbide (a‐SiC:H) films deposited on a‐Si:H film were diffused into the a‐Si:H film. We suggest that the carbon atoms in the a‐Si:H region are the origin of the decrease of the lifetime and the diffusion coefficient of photoexcited carriers in the a‐Si:H.

Investigation of the optogalvanic effect in a microwave discharge

Laser‐induced perturbations of the electron temperature and the electron density are measured by using a Langmuir probe on several electronic transitions in He, Ne, and Ar under a microwave discharge. The electron density either increases or decreases according to the excitation from the nonmetastable or metastable level, respectively. This is consistent with the previous findings in the conventional experiments of the optogalvanic effect. The corresponding electron temperature always decreases with laser excitation showing that the collisional ionization is the dominant process in the discharge. The intensity of the optogalvanic signals is well interpreted in terms of the laser‐induced variation of these plasma parameters.

Ridge Type Microfabrication by Maskless Ion Implantation of Si into SiO2 Film

A ridge type pattern can be fabricated by selective chemical etching after maskless ion implantation of Si++ into SiO2 film. The etchant is buffered HF, and maskless ion implantation into SiO2 film is carried out by a 100 kV focused ion beam apparatus with the ion dose from 2×1016 to 3×1018 cm-2. The ridge line width increases with the ion dose. The cross section of the ridge type pattern is a trapezoidal shape at a wide range of ion dose, while it is a triangular shape at a lower ion dose. The minimum line width of 50 nm with height of about 50 nm is obtained for a conventional CVD SiO2 film.

Surface and interface effects in a-Si:H observed by transient grating spectroscopy

Abstract Carrier dynamics at a free surface and an interface in a-Si:H film were observed by a transient grating spectroscopy. The diffusion coefficients and lifetimes at the surface and in the bulk were determined separately by exciting carriers by selecting the wavelength of the excitation light. The diffusion coefficients and lifetimes in the bulk, at the surface and interfaces decreased in the following order; bulk, a-Si:H free surface, a-Si:H/substrate interface, a-SiC:H/a-Si:H interface.