otes an n-type (first conductivity type) third semiconductor film which is made of a material such as CdS, numeral 2027 denotes a p-type (second conductivity type) fourth semiconductor film which is made of a material such as CdS, symbol H2 denotes a second heterojunction part which is formed by the third and fourth semiconductor films 2026 and 2027, and numeral 2028 denotes second electrodes (fro