Photocurrent Multiplication in Amorphous Silicon Carbide Films

Abstract

This chapter summarizes the details of how photocurrent multiplication in amorphous silicon carbide films was found, and how its mechanism was proposed. Photocurrent multiplication is a phenomenon in which the photocurrent quantum efficiency exceeds unity, and is caused by various amplification effects of the photocurrent. Photocurrent multiplication in amorphous silicon carbide (a-SiC:H) films was first discovered in the simple sandwich-type cell structure of SnO2/a-SiC:H/Au under irradiation with red light (>500 nm). A photocurrent quantum efficiency (that is, the multiplication rate) value of 300 was observed. This phenomenon cannot be attributed to avalanche effects. However, it can be attributed to electron tunneling effects. This means that electron tunneling occurs from the SnO2 electrode to the a-SiC:H film through a thin insulating silicon oxide layer formed at the a-SiC:H/SnO2 interface, which is created by photo-accumulated trapped holes near the interface in a high electric field. Moreover, the multiplied photocurrent was suppressed by superimposing UV-blue light on the red light. The observation of photocurrent multiplication in amorphous inorganic semiconductors led to the discovery of photocurrent multiplication in organic semiconductors, which are described in the remaining chapters in this book.