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.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.