Mitsuo Matsumura

Electrical and Structural Properties of Phosphorous-Doped Glow-Discharge Si:F:H and Si:H Films

Doping of Si:F:H and Si:H with P has been performed by a glow-discharge technique using PH3/SiF4+H2, PF5/SiF4+H2, PH3/SiH4+H2 and PF5/SiH4+H2 gaseous mixtures, and high conductive films over 100 ?-1 cm-1 have been obtained. It has also been made clear from X-ray diffraction and Raman-scattering measurements that all the P-doped Si:F:H films (P/Si>5?10-4) as well as high conductive Si:H films deposited under high RF power condition are polycrystalline, while Si:H films prepared under low power remain amorphous and their conductivity is less than 10-2 ?-1 cm-1. It is likely that film conductivity amounting to 100 ?-1 cm-1 should be ascribed to its polycrystalline structure.

(Invited) Optical, Electrical and Structural Properties of Plasma-Deposited Amorphous Silicon

Amorphous Si: H and Si: F: H films, doped as well as non-doped, have been prepared both by glow-discharge (GD) and reactive-sputtering (SP) methods, and their structural properties have been investigated systematically through X-ray diffraction, Raman scattering, EPMA and ir transmission measurements. Optical and electrical properties are discussed in relation with the contents of Ar, doped element (P), bonded H and dangling bonds and with film structure. It has also been demonstrated that high RF power deposition results in crystallization of Si: H films, independent of whether doped or non-doped, and their structure has been characterized as a mixed phase, consisting microcrystals (100-A size) embedded in amorphous network.

A New Model for the Carrier Transport in Amorphous Si: H Schottky Barrier Diodes

In order to interpret carrier transport in an amorphous silicon Schottky barrier, a new band diagram is proposed. By introducing a phenomenological theory based on the model, relationships between the diode characteristics and the gap states of a-Si: H are discussed. The main results deduced from the theory are as follows: (1) The space-charge density of the depletion region in the barrier is determined mainly by the gap states near the Fermi-energy. (2) The transient space charge limited current flowing when a high forward voltage is applied, decays through the carrier trapping process at the gap states near the Fermi-energy. (3) The breakdown voltage of the diode is closely related with the space-charge due to the localized states at the band tail in the vicinity of a-Si: H/metal interface. Primary experimental results are also presented and discussed.

Preparation and Characterization of Reactively-Sputtered Amorphous Si: H Films

Amorphous Si: H films have been prepared by reactive sputtering of crystalline Si in Ar–H2 mixture, under various deposition conditions of substrate temperature and H2 concentration in sputtering gas, and their optical, structural and electronic properties have been mapped out for the first time. The obtained data have been compared with those of glow discharge a-Si: H film and discussed in a unified manner. It has been demonstrated that bonded H content, Si–H bond configuration, Ar content involved in the film and thermal history are main factors affecting optical and electronic properties. The H content associated with SiH as well as that with SiH2 has been calculated as a function of total H content assuming Poisson distribution, which has been compared with the experimental data.

Characteristics of Schottky Barrier Diodes in Reactively Sputtered Amorphous Si:H

We report a systematic study of Schottky barrier diodes in the reactively-sputtered amorphous Si:H films where we attempt to understand a diode characteristic on the basis of film properties such as bonded H content, optical gap, activation energy of conductivity, spin density and dark- and photoconductivity. The I-V and C-V characteristics are strongly dependent on the bonded H content, suggesting that the effective density of gap states considerably decreases with increasing H content in a-Si:H film. This result is consistent with the independent ESR study of the properties of the film itself.

Observation of valence‐band discontinuity of hydrogenated amorphous silicon/hydrogenated amorphous silicon carbide heterojunction by photocurrent‐voltage measurements

Photocurrent‐voltage measurements at different wavelengths exhibit the valence‐band discontinuity of a hydrogenated amorphous silicon/hydrogenated amorphous silicon carbide heterojunction. A band discontinuity of ∼100 meV is deduced based on a tunneling model for a hole barrier. This energy gap is relatively small compared to that for the conduction band, but significantly affects the characteristics of heterojunction p‐i‐n solar cells.

Evaluation of Boron and Phosphorus Doping Microcrystalline Silicon Films

The change in structure and properties of doped µc-Si films with thickness increase were investigated by ESCA, TEM and IR methods. Dopant contents were analyzed by AES and IMA. The Fermi-level position of phosphorus doped µc-Si, evaluated from Si 2p binding energy by ESCA, was shifted by more than 0.3 eV to conduction band edge with the growth of microcrystallization. Phosphorus doping efficiency in µc-Si was better than that in a-Si at the same dopant density. On the contrary, the Fermi-level position of boron doped µc-Si was almost unchanged in spite of its microcrystallization in the deposition process and high doping.

New Material for p-Type Window Layer in a-Si Solar Cells

We have found a new wide band gap material and applied it as a window layer in a-Si solar cells. Films are deposited by rf-glow discharge method with NO/SiH4/H2 mixtures. IR spectra show that films contain Si, N, O and H (a-Si:O:N:H). Increasing NO/SiH4 ratio, the optical gap widen and the refractive index decreases. The performance of solar cells using an a-Si:O:N:H p-layer has been improved because of the increase in incident light into the i-layer. Moreover, the measurement of photodegradation indicates that the cell efficiency decreases by less than 1% under illumination with AM1 100 mW/cm2 for 10 hrs.