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

采用溅射技术制备了ITO/Cu-ZnS/SiO_2/金属四层结构器件，在外加电压为70V(场强为10.8V/cm)时，器件具有较低的漏电流。只有在400 nm照射后，才能观察到700 nm的瞬时光电流。然而，700 nm和400 nm照射后，吸光度没有变化。这是因为在光照条件下，SiO_2薄膜阻止了Al和Cu-ZS之间的电荷转移。由于AlN具有较宽的禁带宽度和相当大的空穴迁移率，我们采用了AlN作为衬底材料。采用射频反应溅射技术制备了AlN薄膜。在100 W或更高的射频功率下，在蓝宝石衬底上制备了晶态AlN薄膜。在衬底温度高于30 0℃的条件下，在QUART和ITO薄膜上制备了C轴取向的氮化铝薄膜。在沉积AlN薄膜的过程中，ITO/AlN/Al器件的电学性能与衬底温度有关。在70 0℃的条件下，在ITO/AlN/Al器件中沉积的AlN薄膜在70V或更低的电压下没有观察到漏电流。连续的光电流在波长为400 nm处流动，并且在280 nm处有一个峰值。光电流的大小与偏置电压的极性无关，因此光电流来源于AlN的深能级和传导(或价)带之间的光致电荷转移。器件的光吸收在280 nm照射后下降，在380 nm照射后恢复到初始值。在电场存在的情况下，光吸收的变化可以保持几天。这些结果表明，场辅助光致变色是一种有效的光存储方法。

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.