Studies on Electrical Properties of Semiconductor Selenium

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  • セレン半導体の電気的性質について
  • セレン ハンドウタイ ノ デンキテキ セイシツ ニ ツイテ

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As amorphous Se is heated, it transforms to metallic Se and to liquid Se at last. The following is the result of our experiments of how the electrical conductivity and photo-conductivity of Se varies with these transformations.<br>At first, we placed a red Se between platinum electrodes as shown in Fig. 1. We heated them to melt the Se and cooled rapidly. Thus we obtained amorphous Se between the electrodes, which were connected to d.c. amplifier. We then measured the electrical conductivity and photoconductivity of Se while heating.<br>The rate of heatihg was 0.8°C/min. These results are shown in Fig. 4.<br>The electrical conductivity of Se varied with temperature, especially it changed suddenly at the transition point of Se.<br>In Fig. 4, we consider that the part (A) is a amorphous phase, the part (D) a period of crystal growth, and the Se perfectly crystallized in (E). Electrical conductivity of Se begins to decrease rapidly at 220°C and recovers again later. We did not measure the electrical conductivity of Se above 320°C.<br>Next, we measured the electrical conductivity as the temperature went down. The change from (G) to (E) was found to be reversible, but that from (D) to (A) was irreversible. From these results, it seems that the metallic Se is more stable than amorphous one at room temperature and amorphous Se is transformed to metallic Se by heating, but the reverse change does not seem to occur.<br>PHOTO-CONDUCTIVITY IN (B), (C) AND (D).<br>The photo-conductivity in each part of (B), (C) and (D) are shown in Fig. 7. The intensity of incident white light was 36080ergs/cm2·sec and the exposure time was 30sec. We took the maximum deflection of galvanometer in 30sec as the value of photo-current.<br>In Fig. 7, σ is the electrical conductivity in the dark and Δσ is the difference in electrical conductivity between the cases in which the electrode was exposed and not exposed.<br>It is interesting to know that the photo-conductivity reaches its maximum at (D).<br>PHOTO-CONDUCTIVITY IN (H).<br>In this part, we noticed some appreciable photo-currents, but our apparatus could not catch any photo-current at any higher temperature than this.

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