Development of field-assisted photochromism and an application to an optical memeory

点击翻译按钮获取中文摘要

A four-layer device of ITO/Cu-ZnS/SiO_2/metal was fabricated by a sputtering technique ITO/Cu-ZnS/SiO_2/Al devices exhibits low leakage current at an applied voltage of 70 V (an electric filed of 10^8 V/cm). Transient photocurrent at 700 nm is observed only after irradiation of 400 nm. However, no change of absorbance is detected after irradiation of 700 or 400 nm. The reason is that SiO_2 film prevents the charge transfer between Al and Cu-ZnS under light irradiation. Then, we adopted AlN as a host material because AlN has a wide band gap and a considerable hole mobility. AlN films were prepared by RF reactive sputtering technique. Crystalline AlN films were prepared on sapphire substrates under RF power of 100 W or more. C-axis oriented AlN films were deposited on quart and ITO films at a substrate temperate higher than 300℃. The electrical properties of ITO/AlN/Al devices arc dependent on the substrate temperature in the process of deposition of AlN film. No leakage current was observed at 70 Vor less when AlN film in the ITO/AlN/Al device as deposited at 700 ℃. Continuous photocurrent flows at wavelength < 400 nm, and a peak is seen at 280 nm in the spectra of photocurrent. Magnitude of photocurrent is independent of the polarity of a bias voltage, and thus the photocurrent is originated from the photo-induced charge transfer between deep levels and conduction (or valence) bands of AlN.Optical absorbance of the device decreases after the irradiation of 280 nm, and is recovered to the intial value after the irradiation of 380 nm. The change in the optical absorbance is maintained for a few days in the presence of an electric field. These results suggest that the field-assisted photochromism is a powerful method as an optical memory.