Tomokazu Nagao

Characterization of Plasma-Irradiated SiO2/Si Interface Properties by Photoinduced-Carrier Microwave Absorption Method

We report photoinduced carrier recombination induced by 13.56 MHz radio frequency argon plasma treatment for samples of silicon substrates coated with thermally grown SiO2 layers. The transmissivity of a 9.35 GHz microwave was measured and analyzed under illumination of 532 nm green light to the top or rear surface. Irradiation of argon plasma at 100 W for 5 min caused substantial carrier recombination. The recombination velocity of the plasma-irradiated surface was estimated to be 6000 cm/s. Investigation of 100 kHz capacitance response characteristics as a function of bias voltage for metal oxide p-type silicon structures revealed that irradiation of argon plasma increased the fixed charge density from 3.2×1011 to 3.0×1012 cm-2. Those changes were restored completely by heat treatment at 300 °C in air for 60 min.

Minority Carrier Lifetime Measurements by Photoinduced Carrier Microwave Absorption Method

We propose a measurement system for photoinduced minority carrier absorption of 9.35 GHz microwaves using periodically pulsed light illumination at 620 nm. The ratio of average carrier density when light illumination is ON to that when light illumination is OFF, P, was theoretically analyzed for different light pulse widths. The analysis of P resulted in a formula giving the minority carrier lifetime τeff of silicon under continuous light illumination. τeff for holes was experimentally determined using the formula, and its spatial distribution was obtained to be from 1.0 ×10-3 to 1.28 ×10-3 s for n-type silicon substrates with a thickness of 520 µm coated with 100-nm-thick thermally grown SiO2 layers. We also demonstrated that τeff depended on the means of light illumination for a defective sample. Two different τeff values were obtained, 7 ×10-5 and 1.73 ×10-4 s, in the cases of light illumination to the top surface and rear surface, respectively, when the SiO2 layer was etched up to 2 nm at the top surface.

Surface Passivation of Crystalline Silicon by Combination of Amorphous Silicon Deposition with High-Pressure H2O Vapor Heat Treatment

A high minority carrier effective lifetime τeff of crystalline silicon was achieved by hydrogenated amorphous silicon (a-Si:H) films formed by a combination of plasma-enhanced chemical vapor deposition at 150 °C with high-pressure H2O vapor heat treatment. τeff was 1.6×10-4, 3.0×10-4, and 1.15×10-3 s for n-type silicon substrates coated with 3-, 10-, and 50-nm-thick a-Si:H films treated with 1.0×106 Pa H2O vapor heat treatment between 180 and 300 °C for 1 h. Light-induced passivation enhancement was demonstrated when 620-nm light was illuminated at the 50-nm-thick a-Si:H surface. τeff increased from 8.5×10-4 to 1.15×10-3 s probably caused by field effect passivation induced by hole trapping at the SiOx formed by H2O vapor heat treatment for 1 h. On the other hand, τeff was further increased to 1.2×10-3 s by 1.0×106 Pa H2O vapor heat treatment at 300 °C for 3 h for the sample formed with the 50-nm-thick a-Si:H film. However, no increase in τeff was observed by light illumination at the a-Si:H surface, probably because the SiOx clusters became stable and had no hole trapping property.