High-efficiency and low dark current crystalline selenium-based heterojunction photodiode with a high-quality tellurium nucleation layer
In this study, a high-efficiency and low dark current thin-film crystalline selenium (c-Se)/gallium oxide (Ga2O3) heterojunction photodiode is demonstrated via improving the deposition conditions for the tellurium nucleation layer that prevents the peeling of the selenium film during annealing. The highly (100)-oriented polycrystalline selenium film is grown by employing a thin tellurium (Te) nucleation layer with high-quality crystallinity. The device exhibits high external quantum efficiency in the visible region and extremely low dark current that is below 100 pA/cm2 at a reverse-bias voltage of 15 V at room temperature. The result indicates the high potential of crystalline selenium-based photodiodes to be used as photoconversion layers in imaging devices.
Low-voltage-operation avalanche photodiode based on n-gallium oxide/p-crystalline selenium heterojunction
In this study, we demonstrate the avalanche multiplication phenomenon in a crystalline-selenium (c-Se)-based heterojunction photodiode. The carrier injection from an external electrode, which is considered to be the major factor contributing to dark current at a high electric field, was significantly decreased by employing a thin n-type Ga2O3 layer with a high hole-injection barrier. The fabricated Ga2O3/c-Se diode exhibited extremely high external quantum efficiency of over 100% in the short-wavelength region at a relatively low reverse-bias voltage of ∼20 V. Furthermore, Sn-doping of the Ga2O3 layer increases the carrier concentration; hence, the resulting device has a lower threshold voltage for avalanche multiplication.
Ultrahigh-sensitivity new super-HARP camera
NHK led the world in developing a high-sensitivity Super-HARP pickup tube using the avalanche multiplication effect. The authors have now developed an improved version (2/3- inch, with electromagnetic focusing and electromagnetic deflection) which is eight times more sensitive and has much better lag characteristics. The handy New Super-HARP color camera which uses this newly-developed pickup tube has higher sensitivity than human vision (2000 lux, F/110 equivalent), negligible low lag, and a limiting resolution of over 700 TV lines. It will be a powerful tool in emergency news gathering at night, the production of scientific programs, and other applications.