Simpei Tutihasi

Polarization dependence of the urbach rule in trigonal selenium

Abstract An analysis has been made of the tail region of the optical absorption edge in trigonal Se. An exciton accounts for the Urbach Rule observed for E ⊥ c and indirect transitions are observed for E | c. Two phonon energies may be calculated from the measurements for the two directions of polarization and these are found to be in agreement with those obtained from infrared data.

Electronic Properties of Furan‐Quinone Pigments. I. Charge‐Transport Studies

The electrical properties of a furan‐quinone pigment, 8, 13‐dioxodinaphtho (2, 1−b:2′, 3′−d)‐furan‐6‐(2‐pyridyl)‐carboxamide (DFC), have been studied by means of photoinduced condenser discharge and transient photocurrent techniques. It is shown that the electron range in DFC, ∼10−8 cm2 V−1, is 3 orders of magnitude longer than that of holes, ∼10−11 cm2 V−1. The quantum efficiency of the photogeneration of charge carriers in DFC increases linearly with the square of the electric field, while the dark current increases linearly with the square root of the field. The dark current is determined by the number of free carriers in the bulk and may be described in terms of thermally assisted tunnelling.

Exciton spectrum of trigonal selenium at 20°K

Abstract We have studied the reflectivity spectrum of trigonal selenium at 300 and 20°K. A sharp structure has been found at 20°K at the absorption edge. The first peak at 1.940 eV has been interpreted as being due to the exciton absorption. Based on the polarization charateristics of the spectrum, the band structure near the edge is discussed.

Photoconductivity of amorphous As2Se3

It is shown that a blocking contact on a‐As2Se3 becomes injecting upon trapping photogenerated electrons. The blocking contact consists of a thin organic insulator layer between a semitransparent gold anode and the photoconductor. Gains exceeding unity have been observed. The dynamics of the blocking‐to‐injecting contact transition have been investigated, and its process has been interpreted in terms of thermally assisted tunneling. This effect, in which one observes a blocking contact and an injecting contact in one sample, allows one to study both the primary and the conduction photocurrents in a sequential manner in a‐As2Se3. Applying this technique, the steady‐state photoconductivity of a‐As2Se3 has also been investigated in detail. The results of the steady‐state photocurrent measurements are examined in terms of the classical photoconductivity theory.