Low-voltage and high-gain WSe_(2)avalanche phototransistor with an out-of-plane WSe_(2)/WS_(2)heterojunction

The properties of photodetectors based on two-dimensional materials can be significantly enhanced by avalanche effect.However,a high avalanche breakdown voltage is needed to reach impact ionization,which leads to high power consumption.Here,we report the unique features of a low-voltage avalanche phototransistor formed by an in-plane WSe_(2)field effect transistor(FET)with an out-of-plane WSe_(2)/WS_(2)P–N heterojunction(HJ FET).The avalanche breakdown voltage in the device can be decreased from−31 to−8.5 V when compared with that in WSe_(2)FET.The inherent mechanism is mainly related to the redistributed electric field in the WSe_(2)channel after the formation of the out-of-plane P–N heterojunction.When the bias voltage is−16.5 V,the photoresponsivity in the HJ FET is enhanced from 1.5 to 135 A/W,which is significantly higher than that in the WSe_(2)FET because of the obvious reduction of the avalanche breakdown voltage.Moreover,HJ FET shows a higher responsivity than WSe_(2)FET in the range of 400–1,100 nm under low bias voltage.This phenomenon is caused by accelerating electron–hole spatial separation in the heterojunction.These results indicate that the use of an WSe_(2)FET with an out-of-plane WSe_(2)/WS_(2)heterojunction is ideal for high-performance photodetectors with low power consumption.

Modeling,fabrication and measurement of a novel CMOS UV/blue-extended photodiode

A new complementary metal oxide semiconductor UV/blue-extended photodiode was presented for light detection in the UV/blue spectral range. Photoelectric characteristics of this presented photodiode were studied by numerical modeling and device simulation. Technology computer aided design simulation was done first to analyze its photoelectric characteristics. The structure characteristic and depletion situation of space between two adjacent P+ anodes were discussed. The reverse characteristic, spectral response characteristic and DC characteristic were discussed in detail. For the numerical modeling, dead layer effect is considered in the building of analytical mode. Dead layer is a space in which the boron doping profile decreases towards the surface due to high doping effects and boron redistribution, which affects the sensitivity of photodiode in the UV range seriously. Reverse characteristics and spectral response characteristics were modeled and analyzed typically. At last, silicon test results were given and compared with the simulated result, which shows reasonable match for each.